Loss of exudates from the roots of perennial ryegrass inoculated with a range of micro-organisms

To determine the effect of microbial metabolites on the release of root exudates from perennial ryegrass, seedlings were pulse labelled with [¹⁴C]-CO₂ in the presence of a range of soil micro-organisms. Microbial inoculants were spatially separated from roots by Millipore membranes so that root infection did not occur. Using this technique, only microbial metabolites affected root exudation. The effect of microbial metabolites on carbon assimilation and distribution and root exudation was determined for 15 microbial species. Assimilation of a pulse label varied by over 3.5 fold, dependent on inoculant. Distribution of the label between roots and shoots also varied with inoculant, but the carbon pool that was most sensitive to inoculation was root exudation. In the absence of a microbial inoculant only 1% of assimilated label was exuded. Inoculation of the microcosms always caused an increase in exudation but the percentage exuded varied greatly, within the range of 3-34%. © 1995 Kluwer Academic Publishers.

Antimicrobial activity of neuropeptides against a range of micro-organisms from skin, oral, respiratory and gastrointestinal tract sites

Many neuropeptides are similar in size, amino acid composition and charge to antimicrobial peptides. This study aimed to determine whether the neuropeptides substance P (SP), neurokinin A (NKA), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP), displayed antimicrobial activity against Streptococcus mutans, Lactobacillus acidophilus, Enterococcus faecalis, Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans. SP, NPY, VIP and CGRP displayed variable degrees of antimicrobial activity against all the pathogens tested with the exception of S. aureus. These antimicrobial activities add a further dimension to the immunomodulatory roles for neuropeptides in the inflammatory and immune responses. (c) 2008 Elsevier B.V. All rights reserved.

A preliminary survey of micro-organisms in the gut and pellets of a tropical millipede Doratogonus uncinatus Attems (Diplopoda, Spirostreptida, Spirostreptidae).

Millipede gut microbiology and decomposition of faecal pellets over a period of eight weeks were studied in the laboratory. Bacterial numbers, carbon and nitrogen content, pH and weight loss were monitored. Heterotrophic bacteria were the most abundant and reached a peak in the first two weeks of decomposition. The amount of carbon was constant while ammonium nitrogen decreased from 1.51 % to 0.03 % after eight weeksThe pH of the pellets was slightly acidic and did not change much during the course of decomposition. A succession of micro-organisms was observed on decomposing pellets. Zygomycetes were replaced by Ascomycetes after 20 days of decomposition. Decomposition was significantly affected by temperature. The rate of decomposition was highest at 35[degree]C .

The application of TiO2 photocatalysis for disinfection of water contaminated with pathogenic micro-organisms: a review

The use of semiconductor photocatalysis for treatment of water and air has been the topic of intense research activity over the past 20 years. This powerful process has also been extended to the disinfection of environments contaminated with pathogenic micro-organisms. This review summarizes recent developments concerned with the photocatalytic treatment of water contaminated with pathogenic micro-organisms presenting a potential hazard to animals and human beings.

A comparison of the effectiveness of TiO2 photocatalysis and UVA photolysis for the destruction of three pathogenic micro-organisms

TiO₂ photocatalysis has demonstrated efficacy as a treatment process for water contaminated with chemical pollutants. When exposed to UVA light TiO₂ also demonstrates an effective bactericidal activity. The mechanism of this process has been reported to involve attack by valence band generated hydroxyl radicals. In this study when three common bacterial pathogens, Escherichia coli, Salmonella enterica serovar Enteritidis and Pseudomonas aeruginosa, were exposed to TiO₂ and UVA light a substantial decrease in bacterial numbers was observed. Control experiments in which all three pathogens were exposed to UVA light only resulted in a similar reduction in bacterial numbers. Moreover, exposure to UVA light alone resulted in the production of a smaller than average colony phenotype among the surviving bacteria, for all three pathogens examined, a finding which was not observed following treatment with UVA and TiO₂. Small slow growing colonies have been described for several pathogenic bacteria and are referred to as small colony variants. Several studies have demonstrated an association between small colony variants and persistent, recurrent and antibiotic resistant infections. We propose that the production of small colony variants of pathogenic bacteria following UVA treatment of drinking water may represent a health hazard. As these small colony variants were not observed with the UVA/TiO₂ system this potential hazard is not a risk when using this technology. It would also appear that the bactericidal mechanism is different with the UVA/TiO₂ process compared to when UVA light is used alone.

Microbial analysis of soil and groundwater from a gasworks site and comparison to a sequenced biological reactive barrier remediation process (SEREBAR)

Aims: To investigate the distribution of a polymicrobial community of biodegradative bacteria in (i) soil and groundwater at a former manufactured gas plant (FMGP) site and (ii) in a novel SEquential REactive BARrier (SEREBAR) bioremediation process designed to bioremediate the contaminated groundwater. Methods and Results: Culture-dependent and culture-independent analyses using denaturing gradient gel electrophoresis (DGGE) and polymerase chain reaction (PCR) for the detection of 16S ribosomal RNA gene and naphthalene dioxygenase (NDO) genes of free-living (planktonic groundwater) and attached (soil biofilm) samples from across the site and from the SEREBAR process was applied. Naphthalene arising from groundwater was effectively degraded early in the process and the microbiological analysis indicated a dominant role for Pseudomonas and Comamonas in its degradation. The microbial communities appeared highly complex and diverse across both the sites and in the SEREBAR process. An increased population of naphthalene degraders was associated with naphthalene removal. Conclusion: The distribution of micro-organisms in general and naphthalene degraders across the site was highly heterogeneous. Comparisons made between areas contaminated with polycyclic aromatic hydrocarbons (PAH) and those not contaminated, revealed differences in the microbial community profile. The likelihood of noncultured bacteria being dominant in mediating naphthalene removal was evident. Significance and Impact of the Study: This work further emphasizes the importance of both traditional and molecular-based tools in determining the microbial ecology of contaminated sites and highlights the role of noncultured bacteria in the process.

Micro-arthropod communities under human disturbance: is taxonomic aggregation a valuable tool for detecting multivariate change? Evidence from Mediterranean soil oribatid coenoses

Animal communities are sensitive to environmental disturbance, and several multivariate methods have recently been developed to detect changes in community structure. The complex taxonomy of soil invertebrates constrains the use of the community level in monitoring environmental changes, since species identification requires expertise and time. However, recent literature data on marine communities indicate that little multivariate information is lost in the taxonomic aggregation of species data to high rank taxa. In the present paper, this hypothesis was tested on two oribatid mite (oribatida, Acari) assemblages under two different kinds of disturbance: metal pollution and fires. Results indicate that data sets built at the genus and family systematic rank can detect the effects of disturbance with little loss of information. This is an encouraging result in view of the use of the community level as a preliminary tool for describing patterns of human-disturbed soil ecosystems. (c) 2006 Elsevier SAS. All rights reserved.

The diversity of extradiol dioxygenase (edo) genes in cresol degrading rhodococci from a creosote-contaminated site that express a wide range of degradative abilities.

Analysis of the bacterial population of soil surface samples from a creosote-contaminated site showed that up to 50% of the culturable micro-organisms detected were able to utilise a mixture of cresols. From fifty different microbial isolates fourteen that could utilise more than one cresol isomer were selected and identified by 16S rRNA analysis. Eight isolates were Rhodococcus strains and six were Pseudomonas strains. In general, the Rhodococcus strains exhibited a broader growth substrate range than the Pseudomonas strains. The distribution of various extradiol dioxygenase (edo) genes, previously associated with aromatic compound degradation in rhodococci, was determined for the Rhodococcus strains by PCR detection and Southern-blot hybridization. One strain, Rhodococcus sp. I1 exhibited the broadest growth substrate range and possessed five different edo genes. Gene disruption experiments indicated that two genes (edoC and edoD) were associated with isopropylbenzene and naphthalene catabolism respectively. The other Rhodococcus strains also possessed some of the edo genes and one (edoB) was present in all of the Rhodococcus strains analysed. None of the rhodococcal edo genes analysed were present in the Pseudomonas strains isolated from the site. It was concluded that individual strains of Rhodococcus possess a wide degradative ability and may be very important in the degradation of complex mixtures of substrates found in creosote.

Laterite as a disinfectant.

A groundwater programme monitoring flow and quality of a potable water spring in a slum district in Kampala, Uganda revealed that although latrines acted as the principal means of organic waste disposal for the 1000 plus people living in the spring’s catchment, levels of faecal indicator bacteria (TVC 45 Deg C) in spring discharge remained at or below detection during the dry season, despite the presence of high levels of chloride (45mg/l-56mg/l) and nitrate (23mg/l – 30mg/l NO3-N), indicating sewage impacts. A programme of column and batch testing of laterite underlying the area provided a means of investigating the soil’s attenuation capacity under more controlled conditions.
X-ray diffraction analyses revealed the laterite to be dominated by quartz and kaolinite with minor (<5% by volume) quantities of haematite. Batch studies revealed that over 99% of bacteriophage adsorbed to haematite in less than 5 minutes. By contrast batch tests on haematite-free soil samples from the Blue Hills in Australia showed that although they had comparable dominant mineralogy and iron coverage on their surfaces (determined from Energy dispersive X-ray fluorescence) they had negligible ability to adsorb H40/1.
Based on the results of the batch studies using natural soils, a programme of batch studies, undertaken using pure haematite showed the mineral to have an extremely high capacity to adsorb bacteriophage, and suggested that it was responsible for the levels of attenuation observed.
The results of column studies were in keeping with the findings of batch experiments. Injection of 20 pore volumes of 300 pfu/mL of the bacteriophage H40/1 into a 20mm diameter glass column packed with sand sized (Ø>500µm) laterite revealed that the column could irreversibly remove over 2.5 log10 bacteriophage over its 10cm length.
Importance:
Mineralogical and batch test data provide convincing evidence to show that laterite can potentially act as an inexpensive means of removing micro organisms from water. The material, particularly in nodular form, displays considerable potential to act as an alternative filter material to conventional quartz filter sands.

Using solute/ micro organism comparative tracer testing to investigate hydrogeological heterogeneity in a fluvioglacial sand and gravel aquifer.

Groundwater drawn from fluvioglacial sand and gravel aquifers form the principal source of drinking water in many part of central Western Europe. High population densities and widespread organic agriculture in these same areas constitute hazards that may impact the microbiological quality of many potable supplies. Tracer testing comparing two similarly sized bacteria (E.coli and P. putida) and the smaller bacteriophage (H40/1) with the response of non-reactive solute tracer (uranine) at the decametre scale revealed that all tracers broke through up to 100 times more quickly than anticipated using conventional rules of thumb. All microbiological tracer responses were less disperse than the solute, although bacterial peak relative concentrations consistently exceeded those of the solute tracer at one sampling location reflecting exclusion processes influencing micro biological tracer migration. Relative recoveries of H40/1 and E.coli proved consistent at both monitoring wells, while responses of H40/1 and P.putida differed. Examination of exposures of the upper reaches of the aquifer in nearby sand and gravel quarries revealed the aquifer to consist of laterally extensive layers of open framework (OW) gravel enveloped in finer grained gravelly sand. Granulometric analysis of these deposits suggested that the OW gravel was up to two orders of magnitude more permeable than the surrounding deposits giving rise to the preferential flow paths. By contrast fine grained lenses of silty sand within the OW gravels are suspected to play an important role in the exclusion processes that permit solutes to access them but exclude larger micro organisms.

Field fluxes and speciation of arsines emanating from soils

The biogeochemical cycle of arsenic (As) has been extensively studied over the past decades because As is an environmentally ubiquitous, nonthreshold carcinogen, which is often elevated in drinking water and food. It has been known for over a century that micro-organisms can volatilize inorganic As salts to arsines (arsine AsH(3), mono-, di-, and trimethylarsines, MeAsH(2), Me(2)AsH, and TMAs, respectively), but this part of the As cycle, with the exception of geothermal environs, has been almost entirely neglected because of a lack of suited field measurement approaches. Here, a validated, robust, and low-level field-deployable method employing arsine chemotrapping was used to quantify and qualify arsines emanating from soil surfaces in the field. Up to 240 mg/ha/y arsines was released from low-level polluted paddy soils (11.3 ± 0.9 mg/kg As), primarily as TMAs, whereas arsine flux below method detection limit was measured from a highly contaminated mine spoil (1359 ± 212 mg/kg As), indicating that soil chemistry is vital in understanding this phenomenon. In microcosm studies, we could show that under reducing conditions, induced by organic matter (OM) amendment, a range of soils varied in their properties, from natural upland peats to highly impacted mine-spoils, could all volatilize arsines. Volatilization rates from 0.5 to 70 µg/kg/y were measured, and AsH(3), MeAsH(2), Me(2)AsH, and TMAs were all identified. Addition of methylated oxidated pentavalent As, namely monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA), to soil resulted in elevated yearly rates of volatilization with up to 3.5% of the total As volatilized, suggesting that the initial conversion of inorganic As to MMAA limits the rate of arsine and methylarsines production by soils. The nature of OM amendment altered volatilization quantitatively and qualitatively, and total arsines release from soil showed correlation between the quantity of As and the concentration of dissolved organic carbon (DOC) in the soil porewater. The global flux of arsines emanating from soils was estimated and placed in the context of As atmospheric inputs, with arsines contributing from 0.9 to 2.6% of the global budget.

Eradication of endotracheal tube biofilm by nebulised gentamicin.

Objective: To compare the efficacy of gentamicin, nebulised via the endotracheal tube (ET), with that of parenteral cefotaxime or parenteral cefuroxime in preventing the formation of ET biofilm.

Setting: General intensive care units in two university teaching hospitals.

Design: The microbiology of ET biofilm from 36 ICU patients eligible to receive antibiotic prophylaxis was examined. Peak and trough tracheal concentrations of gentamicin, cefotaxime or cefuroxime were measured in each patient group, on the 2nd day of intubation.

Patients: Twelve patients received gentamicin (80 mg) nebulised in 4 ml normal saline every 8 h, 12 cefotaxime (1 g, 12 hourly) and 12 cefuroxime (750 mg, 8 hourly). Prophylaxis was continued for the duration of intubation.

Measurements and results: Samples of tracheal secretions were taken on the 2nd day of ventilation for determination of antibiotic concentrations. Following extubation, ETs were examined for the presence of biofilm. Pathogens considered to be common aetiological agents for VAP included Staphylococcus aureus, enterococci, Enterobacteriaceae and pseudomonads. While microbial biofilm was found on all ETs from the cephalosporin group, microbial biofilm of these micro-organisms was found on 7 of the 12 ET tubes from patients receiving cefotaxime [S. aureus (4), pseudomonads (1), Enterobacteriaceae (1), enterococcus (1)] and 8 of the 12 ET tubes from patients receiving cefuroxime [Enterobacteriaceae (6), P. aeruginosa (1) and enterococcus (1)]. While microbial biofilm was observed on five ETs from patients receiving nebulised gentamicin, none of these were from pathogens for ventilator-associated pneumonia (VAP). Tracheal concentrations of both cephalosporins were lower than those needed to inhibit the growth of pathogens recovered from ET tube biofilm. The median (and range) concentrations for cefotaxime were 0.90 (<0.23–1.31) mg/l and 0.28 (<0.23–0.58) mg/l for 2 h post-dose and trough samples, respectively. Two hours post-dose concentrations of cefuroxime (median and range) were 0.40 (0.34–0.83) mg/l, with trough concentrations of 0.35 (<0.22–0.47) mg/l. Tracheal concentrations (median and range) of gentamicin measured 1 h post-nebulisation were 790 (352–>1250) mg/l and then, before the next dose, were 436 (250–1000) mg/l.

Conclusion: Nebulised gentamicin attained high concentrations in the ET lumen and was more effective in preventing the formation of biofilm than either parenterally administered cephalosporin and therefore may be effective in preventing this complication of mechanical ventilation.

Use of particulate surrogates for assessing microbial mobility in subsurface ecosystems.

Particulate matter can play a vital role in delivering nutrients and micro organisms to groundwater. This paper uses bacteriophage and microsphere surrogates to study the delivery of particles to the subsurface and demonstrates the potential role that pH and ionic strength can play in limiting particle mobility.