Interactions between harmful algae and calanoid copepods in the Baltic Sea

The aim of the studies reported in this thesis was to examine the feeding interactions between calanoid copepods and toxic algae in the Baltic Sea. The central questions in this research concerned the feeding, survival and egg production of copepods exposed to toxic algae. Furthermore, the importance of copepods as vectors in toxin transfer was examined. The haptophyte Prymnesium parvum, which produces extracellular toxins, was the only studied species that directly harmed copepods. Beside this, it had allelopathic effects (cell lysis) on non-toxic Rhodomonas salina. Copepods that were exposed to P. parvum filtrates died or became severely impaired, although filtrates were not haemolytic (indicative of toxicity in this study). Monospecific Prymnesium cell suspensions, in turn, were haemolytic and copepods in these treatments became inactive, although no clear effect on mortality was detected. These results suggest that haemolytic activity may not be a good proxy of the harmful effects of P. parvum. In addition, P. parvum deterred feeding, and low egestion and suppressed egg production were consequently observed in monospecific suspensions of Prymnesium. Similarly, ingestion and faecal pellet production rates were suppressed in high concentration P. parvum filtrates and in mixtures of P. parvum and R. salina. These results indicate that the allelopathic effects of P. parvum on other algal species together with lowered viability as well as suppressed production of copepods may contribute to bloom formation and persistence. Furthermore, the availability of food for planktivorous animals may be affected due to reduced copepod productivity. Nodularin produced by Nodularia spumigena was transferred to Eurytemora affinis via grazing on filaments of small N. spumigena and by direct uptake from the dissolved pool. Copepods also acquired nodularin in fractions where N. spumigena filaments were absent. Thus, the importance of microbial food webs in nodularin transfer should be considered. Copepods were able to remove particulate nodularin from the system, but at the same time a large proportion of the nodularin disappeared. This indicates that copepods may possess effective mechanisms to remove toxins from their tissues. The importance of microorganisms, such as bacteria, in the degradation of cyanobacterial toxins could also be substantial. Our results were the first reports of the accumulation of diarrhetic shellfish toxins (DSTs) produced by Dinophysis spp. in copepods. The PTX2 content in copepods after feeding experiments corresponded to the ingestion of <100 Dinophysis spp. cells. However, no DSTs were recorded from field-collected copepods. Dinophysis spp. was not selected by the copepods and consumption remained low. It seems thus likely that copepods are an unimportant link in the transfer of DSTs in the northern Baltic Sea.

Food and Indoor Air Isolated Bacillus Non-Protein Toxins: : Structures, Physico-Chemical Properties and Mechanisms of Effects on Eukaryotic Cells

We report here the structures and properties of heat-stable, non-protein, and mammalian cell-toxic compounds produced by spore-forming bacilli isolated from indoor air of buildings and from food. Little information is available on the effects and occurrence of heat-stable non-protein toxins produced by bacilli in moisture-damaged buildings. Bacilli emit spores that move in the air and can serve as the carriers of toxins, in a manner similar to that of the spores of toxic fungi found in contaminated indoor air. Bacillus spores in food cause problems because they tolerate the temperatures applied in food manufacture and the spores later initiate growth when food storage conditions are more favorable. Detection of the toxic compounds in Bacillus is based on using the change in mobility of boar spermatozoa as an indicator of toxic exposure. GC, LC, MS, and nuclear magnetic resonance NMR spectroscopy were used for purification, detection, quantitation, and analysis of the properties and structures of the compounds. Toxicity and the mechanisms of toxicity of the compounds were studied using boar spermatozoa, feline lung cells, human neural cells, and mitochondria isolated from rat liver. The ionophoric properties were studied using the BLM (black-lipid membrane) method. One novel toxin, forming ion channels permeant to K+ > Na+ > Ca2+, was found and named amylosin. It is produced by B. amyloliquefaciens isolated from indoor air of moisture-damaged buildings. Amylosin was purified with an RP-HPLC and a monoisotopic mass of 1197 Da was determined with ESI-IT-MS. Furthermore, acid hydrolysis of amylosin followed by analysis of the amino acids with the GS-MS showed that it was a peptide. The presence of a chromophoric polyene group was found using a NMR spectroscopy. The quantification method developed for amylosin based on RP-HPLC-UV, using the macrolactone polyene, amphotericin B (MW 924), as a reference compound. The B. licheniformis strains isolated from a food poisoning case produced a lipopeptide, lichenysin A, that ruptured mammalian cell membranes and was purified with a LC. Lichenysin A was identified by its protonated molecules and sodium- and potassium- cationized molecules with MALDI-TOF-MS. Its protonated forms were observed at m/z 1007, 1021 and 1035. The amino acids of lichenysin A were analyzed with ESI-TQ-MS/MS and, after acid hydrolysis, the stereoisomeric forms of the amino acids with RP-HPLC. The indoor air isolates of the strain of B. amyloliquefaciens produced not only amylosin but also lipopeptides: the cell membrane-damaging surfactin and the fungicidal fengycin. They were identified with ESI-IT-MS observing their protonated molecules, the sodium- and potassium-cationized molecules and analysing the MS/MS spectra. The protonated molecules of surfactin and fengycin showed m/z values of 1009, 1023, and 1037 and 1450, 1463, 1493, and 1506, respectively. Cereulide (MW 1152) was purified with RP-HPLC from a food poisoning strain of B. cereus. Cereulide was identified with ESI-TQ-MS according to the protonated molecule observed at m/z 1154 and the ammonium-, sodium- and potassium-cationized molecules observed at m/z 1171, 1176, and 1192, respectively. The fragment ions of the MS/MS spectrum obtained from the protonated molecule of cereulide at m/z 1154 were also interpreted. We developed a quantification method for cereulide, using RP-HPLC-UV and valinomycin (MW 1110, which structurally resembles cereulide) as the reference compound. Furthermore, we showed empirically, using the BLM method, that the emetic toxin cereulide is a specific and effective potassium ionophore of whose toxicity target is especially the mitochondria.

Expression Analysis of Host-Induced Genes and Proteins of Potato Pathogen Pectobacterium atrosepticum

Pectobacterium atrosepticum on Gram-negatiivinen bakteeri, joka aiheuttaa perunan tyvi- ja märkämätää. P. atrosepticum bakteerin optimilämpötila on melko alhainen ja se on yleinen lauhkeilla alueilla. Tyvimätä leviää pääasiassa siemenperunan välityksellä ja siksi se on ongelma erityisesti siemenperunan tuotannossa. P. atrosepticum kannan SCRI1043 genomi on julkaistu ja sitä tutkitaan malliorganismina märkä- ja tyvimädän taudinaiheuttamisen ymmärtämiseksi. Tämä opportunistinen taudinaiheuttaja voi elää isäntäkasvissa kuukausia piilevänä, aiheuttamatta näkyviä oireita. Suotuisissa olosuhteissa bakteerit alkavat jakautua ja tuottaa kasvin kudoksia hajottavia entsyymejä. Mädäntyvä kasvimassa tarjoaa ravinteita bakteerien kasvuun ja mahdollistaa isäntäkasvin asuttamisen. Soluseiniä hajottavien entsyymien merkitys taudinaiheuttamisessa on hyvin tunnettu, mutta oireettomasta jaksosta ja taudin alkuvaiheista tiedätään vain vähän. Bakteerin genomi sisältää monia toksiineja, adhesiineja, hemolysiineja ja muita proteiineja, joilla saattaa olla merkitys taudinaiheuttamisessa. Tässä työssä käytettiin proteomiikkaa ja mikrosiruanalysiä P. atrosepticum bakteerin erittyvien proteiinien ja geeniekspression tutkimiseen. Proteiinit, jotka eritetään ulos bakteerista, toimivat todennäköisesti taudinaiheuttamisessa, koska ne ovat suorassa kontaktissa isäntäkasvin kanssa. Analyysit suoritettiin olosuhteissa, jotka muistuttavat kasvin soluvälitilaa: matala pH, vähän ravinteita ja matala lämpötila. Isäntäkasvin läsnäolon vaikutusta proteiinien tuottoon ja geeniekspressioon tutkittiin lisäämällä perunauutetta kasvatusalustaan. Tutkimuksessa tunnistettiin P. atrosepticum bakteerin monia jo tunnettuja ja mahdollisesti taudinaiheuttamiseen liittyviä proteiineja. Perunauute lisäsi hiljattain tunnistetun, proteiinien eritysreittiä (tyyppi VI sekreetio, T6SS) koodaavien geenien ilmentymistä. Lisäksi bakteerin havaittiin erittävän useita T6SS:n liittyviä proteiineja kasvualustaan, johon oli lisätty perunauutetta. T6SS:n merkitys bakteereille on vielä epäselvä ja sen vaikutuksesta taudinaiheuttamiseen on julkaistu ristiriitaisia tuloksia. Märkä- ja tyvimädän ymmärtäminen molekulaarisella tasolla luo pohjan tautien kontrollointiin tähtäävään soveltavaan tutkimukseen. Tämä tutkimus lisää tietoa kasvi-patogeeni- interaktiosta ja sitä voidaan tulevaisuudessa käyttää hyväksi esimerkiksi diagnostiikassa, resistenttien perunalajikkeiden jalostuksessa tai viljely- ja varastointiolosuhteiden parantamisessa.

Evolution and detection of cyanobacterial hepatotoxin synthetase genes

Mass occurrences (blooms) of cyanobacteria are common in aquatic environments worldwide. These blooms are often toxic, due to the presence of hepatotoxins or neurotoxins. The most common cyanobacterial toxins are hepatotoxins: microcystins and nodularins. In freshwaters, the main producers of microcystins are Microcystis, Anabaena, and Planktothrix. Nodularins are produced by strains of Nodularia spumigena in brackish waters. Toxic and nontoxic strains of cyanobacteria co-occur and cannot be differentiated by conventional microscopy. Molecular biological methods based on microcystin and nodularin synthetase genes enable detection of potentially hepatotoxic cyanobacteria. In the present study, molecular detection methods for hepatotoxin-producing cyanobacteria were developed, based on microcystin synthetase gene E (mcyE) and the orthologous nodularin synthetase gene F (ndaF) sequences. General primers were designed to amplify the mcyE/ndaF gene region from microcystin-producing Anabaena, Microcystis, Planktothrix, and Nostoc, and nodularin-producing Nodularia strains. The sequences were used for phylogenetic analyses to study how cyanobacterial mcy genes have evolved. The results showed that mcy genes and microcystin are very old and were already present in the ancestor of many modern cyanobacterial genera. The results also suggested that the sporadic distribution of biosynthetic genes in modern cyanobacteria is caused by repeated gene losses in the more derived lineages of cyanobacteria and not by horizontal gene transfer. Phylogenetic analysis also proposed that nda genes evolved from mcy genes. The frequency and composition of the microcystin producers in 70 lakes in Finland were studied by conventional polymerase chain reaction (PCR). Potential microcystin producers were detected in 84% of the lakes, using general mcyE primers, and in 91% of the lakes with the three genus-specific mcyE primers. Potential microcystin-producing Microcystis were detected in 70%, Planktothrix in 63%, and Anabaena in 37% of the lakes. The presence and co-occurrence of potential microcystin producers were more frequent in eutrophic lakes, where the total phosphorus concentration was high. The PCR results could also be associated with various environmental factors by correlation and regression analyses. In these analyses, the total nitrogen concentration and pH were both associated with the presence of multiple microcystin-producing genera and partly explained the probability of occurrence of mcyE genes. In general, the results showed that higher nutrient concentrations increased the occurrence of potential microcystin producers and the risk for toxic bloom formation. Genus-specific probe pairs for microcystin-producing Anabaena, Microcystis, Planktothrix, and Nostoc, and nodularin-producing Nodularia were designed to be used in a DNA-chip assay. The DNA-chip can be used to simultaneously detect all these potential microcystin/nodularin producers in environmental water samples. The probe pairs detected the mcyE/ndaF genes specifically and sensitively when tested with cyanobacterial strains. In addition, potential microcystin/nodularin producers were identified in lake and Baltic Sea samples by the DNA-chip almost as sensitively as by quantitative real-time PCR (qPCR), which was used to validate the DNA-chip results. Further improvement of the DNA-chip assay was achieved by optimization of the PCR, the first step in the assay. Analysis of the mcy and nda gene clusters from various hepatotoxin-producing cyanobacteria was rewarding; it revealed that the genes were ancient. In addition, new methods detecting all the main producers of hepatotoxins could be developed. Interestingly, potential microcystin-producing cyanobacterial strains of Microcystis, Planktothrix, and Anabaena, co-occurred especially in eutrophic and hypertrophic lakes. Protecting waters from eutrophication and restoration of lakes may thus decrease the prevalence of toxic cyanobacteria and the frequency of toxic blooms.

Bacillus cereus spores and cereulide in food-borne illness

B. cereus is a gram-positive bacterium that possesses two different forms of life:the large, rod-shaped cells (ca. 0.002 mm by 0.004 mm) that are able to propagate and the small (0.001 mm), oval shaped spores. The spores can survive in almost any environment for up to centuries without nourishment or water. They are insensitive towards most agents that normally kill bacteria: heating up to several hours at 90 ºC, radiation, disinfectants and extreme alkaline (≥ pH 13) and acid (≤ pH 1) environment. The spores are highly hydrophobic and therefore make them tend to stick to all kinds of surfaces, steel, plastics and live cells. In favorable conditions the spores of B. cereus may germinate into vegetative cells capable of producing food poisoning toxins. The toxins can be heat-labile protein formed after ingestion of the contaminated food, inside the gastrointestinal tract (diarrhoeal toxins), or heat stable peptides formed in the food (emesis causing toxin, cereulide). Cereulide cannot be inactivated in foods by cooking or any other procedure applicable on food. Cereulide in consumed food causes serious illness in human, even fatalities. In this thesis, B. cereus strains originating from different kinds of foods and environments and 8 different countries were inspected for their capability of forming cereulide. Of the 1041 isolates from soil, animal feed, water, air, used bedding, grass, dung and equipment only 1.2 % were capable of producing cereulide, whereas of the 144 isolates originating from foods 24 % were cereulide producers. Cereulide was detected by two methods: by its toxicity towards mammalian cells (sperm assay) and by its peculiar chemical structure using liquid-chromatograph-mass spectrometry equipment. B. cereus is known as one of the most frequent bacteria occurring in food. Most foods contain more than one kind of B. cereus. When randomly selected 100 isolates of B. cereus from commercial infant foods (dry formulas) were tested, 11% of these produced cereulide. Considering a frequent content of 103 to 104 cfu (colony forming units) of B. cereus per gram of infant food formula (dry), it appears likely that most servings (200 ml, 30 g of the powder reconstituted with water) may contain cereulide producers. When a reconstituted infant formula was inoculated with >105 cfu of cereulide producing B. cereus per ml and left at room temperature, cereulide accumulated to food poisoning levels (> 0.1 mg of cereulide per serving) within 24 hours. Paradoxically, the amount of cereulide (per g of food) increased 10 to 50 fold when the food was diluted 4 - 15 fold with water. The amount of the produced cereulide strongly depended on the composition of the formula: most toxin was formed in formulas with cereals mixed with milk, and least toxin in formulas based on milk only. In spite of the aggressive cleaning practices executed by the modern dairy industry, certain genotypes of B. cereus appear to colonise the silos tanks. In this thesis four strategies to explain their survival of their spores in dairy silos were identified. First, high survival (log 15 min kill ≤ 1.5) in the hot alkaline (pH >13) wash liquid, used at the dairies for cleaning-in-place. Second, efficient adherence of the spores to stainless steel from cold water. Third, a cereulide producing group with spores characterized by slow germination in rich medium and well preserved viability when exposed to heating at 90 ºC. Fourth, spores capable of germinating at 8 ºC and possessing the psychrotolerance gene, cspA. There were indications that spores highly resistant to hot 1% sodium hydroxide may be effectively inactivated by hot 0.9% nitric acid. Eight out of the 14 dairy silo tank isolates possessing hot alkali resistant spores were capable of germinating and forming biofilm in whole milk, not previously reported for B. cereus. In this thesis it was shown that cereulide producing B. cereus was capable of inhibiting the growth of cereulide non-producing B. cereus occurring in the same food. This phenomenon, called antagonism, has long been known to exist between B. cereus and other microbial species, e.g. various species of Bacillus, gram-negative bacteria and plant pathogenic fungi. In this thesis intra-species antagonism of B. cereus was shown for the first time. This brother-killing did not depend on the cereulide molecule, also some of the cereulide non-producers were potent antagonists. Interestingly, the antagonistic clades were most frequently found in isolates from food implicated with human illness. The antagonistic property was therefore proposed in this thesis as a novel virulence factor that increases the human morbidity of the species B. cereus, in particular of the cereulide producers.

Assessment and control of Bacillus cereus emetic toxin in food

Despite of improving levels of hygiene, the incidence of registered food borne disease has been at the same level for many years: there were 40 to 90 epidemics in which 1000-9000 persons contracted food poisoning through food or drinking water in Finland. Until the year 2004 salmonella and campylobacter were the most common bacterial causes of food borne diseases, but in years 2005-2006 Bacillus cereus was the most common. Similar developement has been published i.e. in Germany already in the 1990´s. One reason for this can be Bacillus cereus and its emetic toxin, cereulide. Bacillus cereus is a common environmental bacterium that contaminates raw materials of food. Otherwise than salmonella and campylobacter, Bacillus cereus is a heat resistant bacterium, capable of surviving most cooking procedures due to the production of highly thermo resistant spores. The food involved has usually been heat treated and surviving spores are the source of the food poisoning. The heat treatment induces germination of the spore and the vegetative cells then produce toxins. This doctoral thesis research focuses on developing methods for assessing and eliminating risks to food safety by cereulide producing Bacillus cereus. The biochemistry and physiology of cereulide production was investigated and the results were targeted to offer tools for minimizing toxin risk in food during the production. I developed methods for the extraction and quantitative analysis of cereulide directly from food. A prerequisite for that is knowledge of the chemical and physical properties of the toxin. Because cereulide is practically insoluble in water, I used organic solvents; methanol, ethanol and pentane for the extraction. For extraction of bakery products I used high temperature (100C) and pressure (103.4 bars). Alternaties for effective extraction is to flood the plain food with ethanol, followed by stationary equilibration at room temperature. I used this protocol for extracting cereulide from potato puree and penne. Using this extraction method it is also possible also extract cereulide from liquid food, like milk. These extraction methods are important improvement steps for studying of Bacillus cereus emetic food poisonings. Prior my work, cereulide extraction was done using water. As the result, the yield was poor and variable. To investigate suspected food poisonings, it is important to show actual toxicity of the incriminated food. Many toxins, but not cereulide, inactivate during food processing like heating. The next step is to identify toxin by chemical methods. I developed with my colleague Maria Andesson a rapid assay for the detection of cereulide toxicity, within 5 to 15 minutes. By applying this test it is possible to rapidly detect which food was causing the food poisoning. The chemical identification of cereulide was achieved using mass spectrometry. I used cereulide specific molecular ions, m/z (+/-0.3) 1153.8 (M+H+), 1171.0 (M+NH4+), 1176.0 (M+Na+) and 1191.7 (M+K+) for reliable identification. I investigated foods to find out their amenability to accumulate cereulide. Cereulide was formed high amounts (0.3 to 5.5 microg/g wet wt) when of cereulide producing B. cereus strains were present in beans, rice, rice-pastry and meat-pastry, if stored at non refrigerated temperatures (21-23C). Rice and meat pastries are frequently consumed under conditions where no cooled storage is available e.g. picnics and outdoor events. Bacillus cereus is a ubiquitous spore former and is therefore difficult to eliminate from foods. It is therefore important to know which conditions will affect the formation of cereulide in foods. My research showed that the cereulide content was strongly (10 to 1000 fold differences in toxin content) affected by the growth environment of the bacterium. Storage of foods under nitrogen atmosphere (> 99.5 %) prevented the production of cereulide. But when also carbon dioxide was present, minimizing the oxygen contant (< 1%) did not protect the food from formation of cereulide in preliminary experiments. Also food supplements affected cereulide production at least in the laboratory. Adding free amino acids, leucine and valine, stimulated cereulide production 10 to 20 fold. In peptide bonded form these amino acids are natural constituents in all proteins. Interestingly, adding peptide bonded leucine and valine had no significant effect on cereulide production. Free amino acids leucine and valine are approved food supplements and widely used as flawour modifiers in food technology. My research showed that these food supplements may increase food poisoning risk even though they are not toxic themselves.

Heterotrophic Bacteria Associated with Cyanobacteria in Recreational and Drinking Water

Cyanobacterial mass occurrences, also known as water blooms, have been associated with adverse health effects of both humans and animals. They can also be a burden to drinking water treatment facilities. Risk assessments of the blooms have generally focused on the cyanobacteria themselves and their toxins. However, heterotrophic bacteria thriving among cyanobacteria may also be responsible for many of the adverse health effects, but their role as the etiological agents of these health problems is poorly known. In addition, studies on the water purification efficiency of operating water treatment plants during cyanobacterial mass occurrences in their water sources are rare. In the present study, over 600 heterotrophic bacterial strains were isolated from natural freshwater, brackish water or from treated drinking water. The sampling sites were selected as having frequent cyanobacterial occurrences in the water bodies or in the water sources of the drinking water treatment plants. In addition, samples were taken from sites where cyanobacterial water blooms were surmised to have caused human health problems. The isolated strains represented bacteria from 57 different genera of the Gamma-, Alpha- or Betaproteobacteria, Actinobacteria, Flavobacteria, Sphingobacteria, Bacilli and Deinococci classes, based on their partial 16S rRNA sequences. Several isolates had no close relatives among previously isolated bacteria or cloned 16S rRNA genes of uncultivated bacteria. The results show that water blooms are associated with a diverse community of cultivable heterotrophic bacteria. Chosen subsets of the isolated strains were analysed for features such as their virulence gene content and possible effect on cyanobacterial growth. Of the putatively pathogenic haemolytic strains isolated in the study, the majority represented the genus Aeromonas. Therefore, the Aeromonas spp. strains isolated from water samples associated with adverse health effects were screened for the virulence gene types encoding for enterotoxins (ast, alt and act/aerA/hlyA), flagellin subunits (flaA/flaB), lipase (lip/pla/lipH3/alp-1) and elastase (ahyB) by PCR. The majority (90%) of the Aeromonas strains included one or more of the six screened Aeromonas virulence gene types. The most common gene type was act, which was present in 77% of the strains. The fla, ahyB and lip genes were present in 30 37% of the strains. The prevalence of the virulence genes implies that the Aeromonas may be a factor in some of the cyanobacterial associated health problems. Of the 183 isolated bacterial strains that were studied for possible effects on cyanobacterial growth, the majority (60%) either enhanced or inhibited growth of cyanobacteria. In most cases, they enhanced the growth, which implies mutualistic interactions. The results indicate that the heterotrophic bacteria have a role in the rise and fall of the cyanobacterial water blooms. The genetic and phenotypic characteristics and the ability to degrade cyanobacterial hepatotoxins of 13 previously isolated Betaproteobacteria strains, were also studied. The strains originated from Finnish lakes with frequent cyanobacterial occurrence. Tested strains degraded microcystins -LR and -YR and nodularin. The strains could not be assigned to any described bacterial genus or species based on their genetic or phenotypic features. On the basis of their characteristics a new genus and species Paucibacter toxinivorans was proposed for them. The water purification efficiency of the drinking water treatment processes during cyanobacterial water bloom in water source was assessed at an operating surface water treatment plant. Large phytoplankton, cyanobacterial hepatotoxins, endotoxins and cultivable heterotrophic bacteria were efficiently reduced to low concentrations, often below the detection limits. In contrast, small planktonic cells, including also possible bacterial cells, regularly passed though the water treatment. The passing cells may contribute to biofilm formation within the water distribution system, and therefore lower the obtained drinking water quality. The bacterial strains of this study offer a rich source of isolated strains for examining interactions between cyanobacteria and the heterotrophic bacteria associated with them. The degraders of cyanobacterial hepatotoxins could perhaps be utilized to assist the removal of the hepatotoxins during water treatment, whereas inhibitors of cyanobacterial growth might be useful in controlling cyanobacterial water blooms. The putative pathogenicity of the strains suggests that the health risk assessment of the cyanobacterial blooms should also cover the heterotrophic bacteria.

Harmful algae in the planktonic food web of the Baltic Sea

This study deals with algal species occurring commonly in the Baltic Sea: haptophyte Prymnesium parvum, dinoflagellates Dinophysis acuminata, D. norvegica and D. rotundata, and cyanobacterium Nodularia spumigena. The hypotheses are connected to the toxicity of the species, to the factors determining toxicity, to the consequences of toxicity and to the transfer of toxins in the aquatic food web. Since the Baltic Sea is severely eutrophicated, the fast-growing haptophytes have potential in causing toxic blooms. In our studies, the toxicity (as haemolytic activity) of the haptophyte P. parvum was highest under phosphorus-limited conditions, but the cells were toxic also under nitrogen limitation and under nutrient-balanced growth conditions. The cellular nutrient ratios were tightly related to the toxicity. The stoichiometric flexibility for cellular phosphorus quota was higher than for nitrogen, and nitrogen limitation led to decreased biomass. Negative allelopathic effects on another algae (Rhodomonas salina) could be observed already at low P. parvum cell densities, whereas immediate lysis of R. salina cells occurred at P. parvum cell densities corresponding to natural blooms. Release of dissolved organic carbon from the R. salina cells was measured within 30 minutes, and an increase in bacterial number and biomass was measured within 23 h. Because of the allelopathic effect, formation of a P. parvum bloom may accelerate after a critical cell density is reached and the competing species are eliminated. A P. parvum bloom indirectly stimulates bacterial growth, and alters the functioning of the planktonic food web by increasing the carbon transfer through the microbial loop. Our results were the first reports on DSP toxins in Dinophysis cells in the Gulf of Finland and on PTX-2 in the Baltic Sea. Cellular toxin contents in Dinophysis spp. ranged from 0.2 to 149 pg DTX-1 cell-1 and from 1.6 to 19.9 pg PTX-2 cell-1 in the Gulf of Finland. D. norvegica was found mainly around the thermocline (max. 200 cells L-1), whereas D. acuminata was found in the whole mixed layer (max. 7 280 cells L-1). Toxins in the sediment trap corresponded to 1 % of DTX-1 and 0.01 % PTX-2 of the DSP pool in the suspended matter. This indicates that the majority of the DSP toxins does not enter the benthic community, but is either decomposed in the water column, or transferred to higher trophic levels in the planktonic food chain. We found that nodularin, produced by Nodularia spumigena, was transferred to the copepod Eurytemora affinis through three pathways: by grazing on filaments of small Nodularia, directly from the dissolved pool, and through the microbial food web by copepods grazing on ciliates, dinoflagellates and heterotrophic nanoflagellates. The estimated proportion of the microbial food web in nodularin transfer was 22-45 % and 71-76 % in our two experiments, respectively. This highlights the potential role of the microbial food web in the transfer of toxins in the planktonic food web.

Characterization of genomic diversity in extraintestinal pathogenic Escherichia coli (ExPEC) and development of a diagnostic DNA microarray for the differentiation of ExPEC isolates causing urinary tract infections

Extraintestinal pathogenic Escherichia coli (ExPEC) represent a diverse group of strains of E. coli, which infect extraintestinal sites, such as the urinary tract, the bloodstream, the meninges, the peritoneal cavity, and the lungs. Urinary tract infections (UTIs) caused by uropathogenic E. coli (UPEC), the major subgroup of ExPEC, are among the most prevalent microbial diseases world wide and a substantial burden for public health care systems. UTIs are responsible for serious morbidity and mortality in the elderly, in young children, and in immune-compromised and hospitalized patients. ExPEC strains are different, both from genetic and clinical perspectives, from commensal E. coli strains belonging to the normal intestinal flora and from intestinal pathogenic E. coli strains causing diarrhea. ExPEC strains are characterized by a broad range of alternate virulence factors, such as adhesins, toxins, and iron accumulation systems. Unlike diarrheagenic E. coli, whose distinctive virulence determinants evoke characteristic diarrheagenic symptoms and signs, ExPEC strains are exceedingly heterogeneous and are known to possess no specific virulence factors or a set of factors, which are obligatory for the infection of a certain extraintestinal site (e. g. the urinary tract). The ExPEC genomes are highly diverse mosaic structures in permanent flux. These strains have obtained a significant amount of DNA (predictably up to 25% of the genomes) through acquisition of foreign DNA from diverse related or non-related donor species by lateral transfer of mobile genetic elements, including pathogenicity islands (PAIs), plasmids, phages, transposons, and insertion elements. The ability of ExPEC strains to cause disease is mainly derived from this horizontally acquired gene pool; the extragenous DNA facilitates rapid adaptation of the pathogen to changing conditions and hence the extent of the spectrum of sites that can be infected. However, neither the amount of unique DNA in different ExPEC strains (or UPEC strains) nor the mechanisms lying behind the observed genomic mobility are known. Due to this extreme heterogeneity of the UPEC and ExPEC populations in general, the routine surveillance of ExPEC is exceedingly difficult. In this project, we presented a novel virulence gene algorithm (VGA) for the estimation of the extraintestinal virulence potential (VP, pathogenicity risk) of clinically relevant ExPECs and fecal E. coli isolates. The VGA was based on a DNA microarray specific for the ExPEC phenotype (ExPEC pathoarray). This array contained 77 DNA probes homologous with known (e.g. adhesion factors, iron accumulation systems, and toxins) and putative (e.g. genes predictably involved in adhesion, iron uptake, or in metabolic functions) ExPEC virulence determinants. In total, 25 of DNA probes homologous with known virulence factors and 36 of DNA probes representing putative extraintestinal virulence determinants were found at significantly higher frequency in virulent ExPEC isolates than in commensal E. coli strains. We showed that the ExPEC pathoarray and the VGA could be readily used for the differentiation of highly virulent ExPECs both from less virulent ExPEC clones and from commensal E. coli strains as well. Implementing the VGA in a group of unknown ExPECs (n=53) and fecal E. coli isolates (n=37), 83% of strains were correctly identified as extraintestinal virulent or commensal E. coli. Conversely, 15% of clinical ExPECs and 19% of fecal E. coli strains failed to raster into their respective pathogenic and non-pathogenic groups. Clinical data and virulence gene profiles of these strains warranted the estimated VPs; UPEC strains with atypically low risk-ratios were largely isolated from patients with certain medical history, including diabetes mellitus or catheterization, or from elderly patients. In addition, fecal E. coli strains with VPs characteristic for ExPEC were shown to represent the diagnostically important fraction of resident strains of the gut flora with a high potential of causing extraintestinal infections. Interestingly, a large fraction of DNA probes associated with the ExPEC phenotype corresponded to novel DNA sequences without any known function in UTIs and thus represented new genetic markers for the extraintestinal virulence. These DNA probes included unknown DNA sequences originating from the genomic subtractions of four clinical ExPEC isolates as well as from five novel cosmid sequences identified in the UPEC strains HE300 and JS299. The characterized cosmid sequences (pJS332, pJS448, pJS666, pJS700, and pJS706) revealed complex modular DNA structures with known and unknown DNA fragments arranged in a puzzle-like manner and integrated into the common E. coli genomic backbone. Furthermore, cosmid pJS332 of the UPEC strain HE300, which carried a chromosomal virulence gene cluster (iroBCDEN) encoding the salmochelin siderophore system, was shown to be part of a transmissible plasmid of Salmonella enterica. Taken together, the results of this project pointed towards the assumptions that first, (i) homologous recombination, even within coding genes, contributes to the observed mosaicism of ExPEC genomes and secondly, (ii) besides en block transfer of large DNA regions (e.g. chromosomal PAIs) also rearrangements of small DNA modules provide a means of genomic plasticity. The data presented in this project supplemented previous whole genome sequencing projects of E. coli and indicated that each E. coli genome displays a unique assemblage of individual mosaic structures, which enable these strains to successfully colonize and infect different anatomical sites.

A Critical Evaluation of the MARS Treatment in Finland

The Molecular Adsorbent Recirculating System (MARS) is an extracorporeal albumin dialysis device which is used in the treatment of liver failure patients. This treatment was first utilized in Finland in 2001, and since then, over 200 patients have been treated. The aim of this thesis was to evaluate the impact of the MARS treatment on patient outcome, the clinical and biochemical variables, as well as on the psychological and economic aspects of the treatment in Finland. This thesis encompasses 195 MARS-treated patients (including patients with acute liver failure (ALF), acute-on-chronic liver failure (AOCLF) and graft failure), and a historical control group of 46 ALF patients who did not undergo MARS. All patients received a similar standard medical therapy at the same intensive care unit. The baseline data (demographics, laboratory and clinical variables) and MARS treatment-related and health-related quality-of-life data were recorded before and after treatment. The direct medical costs were determined for a period of 3.5 years.Additionally, the outcome of patients (survival, native liver recovery and need for liver transplantation) and survival predicting factors were investigated. In the outcome analysis, for the MARS-treated ALF patients, their 6-month survival (75% vs. 61%, P=0.07) and their native liver recovery rate (49% vs. 17%, P<0.001) were higher, and their need for transplantations was lower (29% vs. 57%, P= 0.001) than for the historical controls. However, the etiological distribution of the ALF patients referred to our unit has changed considerably over the past decade and the percentage of patients with a more favorable prognosis has increased. The etiology of liver failure was the most important predictor of the outcome. Other survival predicting factors in ALF included hepatic encephalopathy, the coagulation factors and the liver enzyme levels prior to MARS treatment. In terms of prognosis, the MARS treatment of the cirrhotic AOCLF patient seems meaningful only when the patient is eligible for transplantation. The MARS treatment appears to halt the progression of encephalopathy and reduce the blood concentration of neuroactive amino acids, albumin-bound and water-soluble toxins. In general, the effects of the MARS treatment seem to stabilize the patients, thus allowing additional time either for the native liver to recover, or for the patients to endure the prolonged waiting for transplantation. Furthermore, for the ALF patients, the MARS treatment appeared to be less costly and more cost-efficient than the standard medical therapy alone. In conclusion, the MARS treatment appears to have a beneficial effect on the patient outcome in ALF and in those AOCLF patients who can be bridged to transplantation.

The challenge of LC/MS/MS multi-mycotoxin analysis - Heracles battling the Hydra?

Mycotoxins are secondary metabolites of filamentous fungi. They pose a health risk to humans and animals due to their harmful biological properties and common occurrence in food and feed. Liquid chromatography/mass spectrometry (LC/MS) has gained popularity in the trace analysis of food contaminants. In this study, the applicability of the technique was evaluated in multi-residue methods of mycotoxins aiming at simultaneous detection of chemically diverse compounds. Methods were developed for rapid determination of toxins produced by fungal genera of Aspergillus, Fusarium, Penicillium and Claviceps from cheese, cereal based agar matrices and grains. Analytes were extracted from these matrices with organic solvents. Minimal sample clean-up was carried out before the analysis of the mycotoxins with reversed phase LC coupled to tandem MS (MS/MS). The methods were validated and applied for investigating mycotoxins in cheese and ergot alkaloid occurrence in Finnish grains. Additionally, the toxin production of two Fusarium species predominant in northern Europe was studied. Nine mycotoxins could be determined from cheese with the method developed. The limits of quantification (LOQ) allowed the quantification at concentrations varying from 0.6 to 5.0 µg/kg. The recoveries ranged between 96 and 143 %, and the within-day repeatability (as relative standard deviation, RSDr) between 2.3 and 12.1 %. Roquefortine C and mycophenolic acid could be detected at levels of 300 up to 12000 µg/kg in the mould cheese samples analysed. A total of 29 or 31 toxins could be analysed with the method developed for agar matrices and grains, with the LOQs ranging overall from 0.1 to 1250 µg/kg. The recoveries ranged generally between 44 and 139 %, and the RSDr between 2.0 and 38 %. Type-A trichothecenes and beauvericin were determined from the cereal based agar and grain cultures of F. sporotrichioides and F. langsethiae. T-2 toxin was the main metabolite, the average levels reaching 22000 µg/kg in the grain cultures after 28 days of incubation. The method developed for ten ergot alkaloids from grains allowed their quantification at levels varying from 0.01 to 10 µg/kg. The recoveries ranged from 51 to 139 %, and the RSDr from 0.6 to 13.9 %. Ergot alkaloids were measured in barley and rye at average levels of 59 and 720 µg/kg, respectively. The two most prevalent alkaloids were ergocornine and ergocristine. The LC/MS methods developed enabled rapid detection of mycotoxins in such applications where several toxins co-occurred. Generally, the performance of the methods was good, allowing reliable analysis of the mycotoxins of interest with sufficiently low quantification limits. However, the variation in validation results highlighted the challenges related to optimising this type of multi-residue methods. New data was obtained about the occurrence of mycotoxins in mould cheeses and of ergot alkaloids in Finnish grains. In addition, the study revealed the high mycotoxin-producing potential of two common fungi in Finnish crops. The information can be useful when risks related to fungal and mycotoxin contamination will be assessed.