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.

Phytoplankton quantity as an indicator of eutrophication in Finnish coastal waters : Applications within the Water Framework Directive

The tackling of coastal eutrophication requires water protection measures based on status assessments of water quality. The main purpose of this thesis was to evaluate whether it is possible both scientifically and within the terms of the European Union Water Framework Directive (WFD) to assess the status of coastal marine waters reliably by using phytoplankton biomass (ww) and chlorophyll a (Chl) as indicators of eutrophication in Finnish coastal waters. Empirical approaches were used to study whether the criteria, established for determining an indicator, are fulfilled. The first criterion (i) was that an indicator should respond to anthropogenic stresses in a predictable manner and has low variability in its response. Summertime Chl could be predicted accurately by nutrient concentrations, but not from the external annual loads alone, because of the rapid affect of primary production and sedimentation close to the loading sources in summer. The most accurate predictions were achieved in the Archipelago Sea, where total phosphorus (TP) and total nitrogen (TN) alone accounted for 87% and 78% of the variation in Chl, respectively. In river estuaries, the TP mass-balance regression model predicted Chl most accurately when nutrients originated from point-sources, whereas land-use regression models were most accurate in cases when nutrients originated mainly from diffuse sources. The inclusion of morphometry (e.g. mean depth) into nutrient models improved accuracy of the predictions. The second criterion (ii) was associated with the WFD. It requires that an indicator should have type-specific reference conditions, which are defined as "conditions where the values of the biological quality elements are at high ecological status". In establishing reference conditions, the empirical approach could only be used in the outer coastal water types, where historical observations of Secchi depth of the early 1900s are available. The most accurate prediction was achieved in the Quark. In the inner coastal water types, reference Chl, estimated from present monitoring data, are imprecise - not only because of the less accurate estimation method but also because the intrinsic characteristics, described for instance by morphometry, vary considerably inside these extensive inner coastal types. As for phytoplankton biomass, the reference values were less accurate than in the case of Chl, because it was possible to estimate reference conditions for biomass only by using the reconstructed Chl values, not the historical Secchi observations. An paleoecological approach was also applied to estimate annual average reference conditions for Chl. In Laajalahti, an urban embayment off Helsinki, strongly loaded by municipal waste waters in the 1960s and 1970s, reference conditions prevailed in the mid- and late 1800s. The recovery of the bay from pollution has been delayed as a consequence of benthic release of nutrients. Laajalahti will probably not achieve the good quality objectives of the WFD on time.    The third criterion (iii) was associated with coastal management including the resources it has available. Analyses of Chl are cheap and fast to carry out compared to the analyses of phytoplankton biomass and species composition; the fact which has an effect on number of samples to be taken and thereby on the reliability of assessments. However, analyses on phytoplankton biomass and species composition provide more metrics for ecological classification, the metrics which reveal various aspects of eutrophication contrary to what Chl alone does.

Development of mass balance models for lakes

Yhteenveto: Järvien ainetasemallien kehittäminen.