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PubMed2004

Combination of polydextrose and lactitol affects microbial ecosystem and immune responses in rat gastrointestinal tract.

The effects of various dietary fibres on gut health have been studied extensively but their combined effects are scarcely documented. In the present study the effects of 2 % (w/w) polydextrose (PDX), 2 % (w/w) disaccharide lactitol, or 2 % (w/w) PDX+2 % (w/w) lactitol on gut microflora, microbial metabolism and gut immune responses were investigated in rats. Both PDX and lactitol alone had an effect on many of the studied parameters, but their combination had stronger than additive effects in some parameters. The PDX+lactitol combination altered the microbial community structure as seen by a culture-independent method, percentage guanine+cytosine (%G+C) profiling, increasing the areas of %G+C 35-39 (P<0.0001) and %G+C 45-49 (P=0.0002), and decreasing %G+C 65-74 (P<0.0003). These changes were also reflected in the microbial metabolism so that the production of biogenic amines and branched volatile fatty acids was significantly reduced, by 12 (P=0.03) and 50 % (P=0.002), respectively, indicating a shift from putrefactive towards saccharolytic metabolism. PDX increased the secretion of IgA in the caecum (P=0.007). Secretion of IgA increased even more, almost ten-fold, with the combination of PDX+lactitol (P<0.0001) when compared with the control group. Lactitol increased the production of butyrate by caecal microbes by two- to three-fold when compared with the PDX or control group (P<0.0001). Butyrate is a preferred energy source for mucosal cells; thus a boost in the availability of energy for immune cells may have still added to the synergistic effects of PDX and lactitol on immune cells. It is noteworthy that improvement in the IgA secretion occurred without signs of mucosal inflammation.

Animals↗

PubMed1985

Fourier transform-infrared spectroscopic methods for microbial ecology: analysis of bacteria, bacteria-polymer mixtures and biofilms.

Fourier transform-infrared (FT-IR) spectroscopy has been used to rapidly and nondestructively analyze bacteria, bacteria-polymer mixtures, digester samples and microbial biofilms. Diffuse reflectance FT-IR (DRIFT) analysis of freeze-dried, powdered samples offered a means of obtaining structural information. The bacteria examined were divided into two groups. The first group was characterized by a dominant amide I band and the second group of organisms displayed an additional strong carbonyl stretch at approximately 1740 cm-1. The differences illustrated by the subtraction spectra obtained for microbes of the two groups suggest that FT-IR spectroscopy can be utilized to recognize differences in microbial community structure. Calculation of specific band ratios has enabled the composition of bacteria and extracellular or intracellular storage product polymer mixtures to be determined for bacteria-gum arabic (amide I/carbohydrate C-O approximately 1150 cm-1) and bacteria-poly-beta-hydroxybutyrate (amide I/carbonyl approximately 1740 cm-1). The key band ratios correlate with the compositions of the material and provide useful information for the application of FT-IR spectroscopy to environmental biofilm samples and for distinguishing bacteria grown under differing nutrient conditions. DRIFT spectra have been obtained for biofilms produced by Vibrio natriegens on stainless steel disks. Between 48 and 144 h, an increase in bands at approximately 1440 and 1090 cm-1 was seen in FT-IR spectra of the V. natriegens biofilm. DRIFT spectra of mixed culture effluents of anaerobic digesters show differences induced by shifts in input feedstocks. The use of flow-through attenuated total reflectance has permitted in situ real-time changes in biofilm formation to be monitored and provides a powerful tool for understanding the interactions within adherent microbial consortia.

Bacterial Physiological Phenomena↗

PubMed2002

Bioaugmentation with the resin acid-degrading bacterium Zoogloea resiniphila DhA-35 to counteract pH stress in an aerated lagoon treating pulp and paper mill effluent.

Efficient and reliable removal of resin acids such as dehydroabietic acid (DhA), which are the major toxicants in pulp and paper mill effluents and form pitch interfering with papermaking, is critically important to prevent toxicity discharge and failure of paper machines. Low- and high-pH stresses sometimes occur in effluent treatment systems due to the use of large amounts of acids and alkalines in the pulping processes. We found that both low- and high-pH stresses (pH 3 and 10, respectively) decreased the removal of total organic carbon and completely inhibited the removal of DhA by the biomass of an aerated lagoon treating pulp mill effluent. The pH stresses caused changes in the bacterial community structure as assessed by ribosomal intergenic spacer length polymorphism. The pH stresses greatly reduced the indigenous DhA-degrading populations in the lagoon community. Bioaugmentation with Zoogloea resiniphila DhA-35, a DhA-degrading bacterium originally isolated from a pulp mill treatment system, restored the DhA removal by both the low- and high-pH-stressed lagoon biomass. This bacterium was persistent after introduction into the lagoon microbial community, and its cellular rRNA:rDNA ratio increased during the period of DhA removal. The introduction of strain DhA-35 changed the microbial community structure, but did not adversely affect the TOC removal by the community. This study suggests that it is feasible and potentially useful to use bioaugmentation with resin-acid-degrading bacteria such as DhA-35 to restore and enhance resin acid removal by aerated lagoon microbial communities.

Biodegradation, Environmental↗

PubMed1997

Distribution of microorganisms in deep-sea hydrothermal vent chimneys investigated by whole-cell hybridization and enrichment culture of thermophilic subpopulations.

The microbial community structure of hydrothermal vent chimneys was evaluated by the combined use of enrichment cultures and whole-cell hybridizations with fluorescently labeled 16S rRNA-based oligonucleotide probes. Chimneys were collected during the Microsmoke cruise on the Mid-Atlantic Ridge and were subsampled on board and stored under reduced conditions or fixed. For estimation of culturable thermophiles, selective media were inoculated by dilution series of the samples and incubated at 65, 80, and 95(deg)C. To analyze the microbial diversity of the samples, cells were extracted from the fixed chimney structure samples and hybridized with domain- and kingdom-specific probes. Quantification of the extracted cells was assessed by whole-cell hybridization on membrane filters. By both methods, the largest amounts of microorganisms were found in the upper and outer parts of the chimneys, although even the inner parts contained culturable and detectable amounts of cells. Different morphotypes of thermophilic and hyperthermophilic microorganisms were enriched and detected in samples. Our data clearly indicate that the morphological diversity observed by using whole-cell hybridization is much larger than that assessed by use of culture-based enrichments. This new approach, including culture-independent and -dependent methods to study hydrothermal vent chimneys, showed an uneven distribution of a diverse microbial community. Application of lower-level specific probes for known families and genera within each domain by our approach will be useful to reveal the real extent and nature of the chimney microbial diversity and to support cultivation attempts.

Journal Article↗

PubMed2026

Comparative metagenomic analysis of microbial communities: unravelling microbial communities from the great Rann of Kachchh and coastal saltpans, Gujarat, India.

Hypersaline environments exhibit extreme physiochemical conditions yet support diverse microbial communities. These communities are not only ecologically important but also possess substantial potential for biotechnological exploitation. In this study, we employed a comparative metagenomic approach to assess microbial diversity using two distinct methodologies: (1) direct DNA extraction from raw sediment, and (2) DNA extraction following halophilic enrichment in selective media. Sediment samples were collected from multiple sites and pooled together within the Rann of Kachchh and close-by saltpans and were analysed using 16S rRNA sequencing coupled with bioinformatics pipelines. The results revealed pronounced differences in microbial community composition between the two approaches. Raw sediment samples exhibited significantly higher alpha diversity, with dominant taxa including Halobacterota, Cyanobacteria, and Desulfobacterota, with a substantial proportion of unclassified genera. In contrast, enriched samples were dominated by fast-growing, culturable genera such as Halobacterium, Alkalibacillus, and Candidatus haloredivivus. Principal Coordinate Analysis (PCoA) of beta diversity demonstrated distinct clustering between raw and enriched communities, even within samples from the same sites, underscoring the selective bias introduced by enrichment procedures. These findings emphasise that the methodological choice strongly influences the observed microbial diversity. The aim of this study was to compare microbial community composition in raw hypersaline sediments and enrichment cultures using metagenomic sequencing, to evaluate how enrichment selectively favours specific halophilic taxa. This comparative approach allows identification of the microbial groups that rapidly proliferate under controlled hypersaline conditions, thereby complementing direct environmental sequencing. By integrating both direct and enrichment-based metagenomic approaches, a more comprehensive understanding of microbial community structure in hypersaline environments can be achieved.

India↗

PubMed2006

Microbial diversity and bioremediation of a hydrocarbon-contaminated aquifer (Vega Baja, Puerto Rico).

Hydrocarbon contamination of groundwater resources has become a major environmental and human health concern in many parts of the world. Our objectives were to employ both culture and culture-independent techniques to characterize the dynamics of microbial community structure within a fluidized bed reactor used to bioremediate a diesel-contaminated groundwater in a tropical environment. Under normal operating conditions, 97 to 99% of total hydrocarbons were removed with only 14 min hydraulic retention time. Over 25 different cultures were isolated from the treatment unit (96% which utilized diesel constituents as sole carbon source). Approximately 20% of the isolates were also capable of complete denitrification to nitrogen gas. Sequence analysis of 16S rDNA demonstrated ample diversity with most belonging to the infinity, beta and gamma subdivision of the Proteobacteria, Bacilli, and Actinobacteria groups. Moreover, the genetic constitution of the microbial community was examined at multiple time points with a Functional Gene Array (FGA) containing over 12,000 probes for genes involved in organic degradation and major biogeochemical cycles. Total community DNA was extracted and amplified using an isothermal phi29 polymerase-based technique, labeled with Cy5 dye, and hybridized to the arrays in 50% formimide overnight at 50 degrees C. Cluster analysis revealed comparable profiles over the course of treatment suggesting the early selection of a very stable microbial community. A total of 270 genes for organic contaminant degradation (including naphthalene, toluene [aerobic and anaerobic], octane, biphenyl, pyrene, xylene, phenanthrene, and benzene); and 333 genes involved in metabolic activities (nitrite and nitrous oxide reductases [nirS, nirK, and nosZ], dissimilatory sulfite reductases [dsrAB], potential metal reducing C-type cytochromes, and methane monooxygenase [pmoA]) were repeatedly detected. Genes for degradation of MTBE, nitroaromatics and chlorinated compounds were also present, indicating a broad catabolic potential of the treatment unit. FGA's demonstrated the early establishment of a diverse community with concurrent aerobic and anaerobic processes contributing to the bioremediation process.

Bacteria↗

PubMed2006

Diversity of fungi, bacteria, and actinomycetes on leaves decomposing in a stream.

Although fungi, bacteria, and specific bacterial taxa, such as the actinomycetes, have been studied extensively in various habitats, few studies have examined them simultaneously, especially on decomposing leaves in streams. In this study, sugar maple and white oak leaves were incubated in a stream in northeastern Ohio for 181 days during which samples were collected at regular intervals. Following DNA extraction, PCR-denaturing gradient gel electrophoresis (DGGE) was performed using fungus-, bacterium-, and actinomycete-specific primers. In addition, fungal and bacterial biomass was estimated. Fungal biomass differed on different days but not between leaves of the two species and was always greater than bacterial biomass. There were significant differences in bacterial biomass through time and between leaf types on some days. Generally, on the basis of DGGE, few differences in community structure were found for different leaf types. However, the ribotype richness of fungi was significantly greater than those of the bacteria and actinomycetes, which were similar to each other. Ribotype richness decreased toward the end of the study for each group except bacteria. Lack of differences between the two leaf types suggests that the microorganisms colonizing the leaf biofilm were primarily generalists that could exploit the resources of the leaves of either species equally well. Thus, we conclude that factors, such as the ecological role of the taxa (generalists versus specialists), stage of decay, and time of exposure, appeared to be more important determinants of microbial community structure than leaf quality.

Acer↗

PubMed2004

Ordination and significance testing of microbial community composition derived from terminal restriction fragment length polymorphisms: application of multivariate statistics.

Terminal restriction fragment length polymorphism (T-RFLP) is increasingly being used to examine microbial community structure and accordingly, a range of approaches have been used to analyze data sets. A number of published reports have included data and results that were statistically flawed or lacked rigorous statistical testing. A range of simple, yet powerful techniques are available to examine community data, however their use is seldom, if ever, discussed in microbial literature. We describe an approach that overcomes some of the problems associated with analyzing community datasets and offer an approach that makes data interpretation simple and effective. The Bray-Curtis coefficient is suggested as an ideal coefficient to be used for the construction of similarity matrices. Its strengths include its ability to deal with data sets containing multiple blocks of zeros in a meaningful manner. Non-metric multi-dimensional scaling is described as a powerful, yet easily interpreted method to examine community patterns based on T-RFLP data. Importantly, we describe the use of significance testing of data sets to allow quantitative assessment of similarity, removing subjectivity in comparing complex data sets. Finally, we introduce a quantitative measure of sample dispersion and suggest its usefulness in describing site heterogeneity.

Bacteria↗

PubMed2026

Pilot metaproteomic profiling reveals bacterial diversity and potential medical and veterinary relevance of tick microbiomes in northern Algeria.

Ticks are major ectoparasites and vectors of pathogens affecting humans, livestock, and wildlife. They harbor diverse microbial communities that may influence tick biology and interactions with microorganisms; however, functional information on tick-associated microbiomes remains limited, particularly in North Africa. In this pilot study, we applied a metaproteomic approach based on high-resolution tandem mass spectrometry to characterize bacterial communities associated with three tick species collected in Algeria: Rhipicephalus sanguineus sensu lato, Hyalomma aegyptium, and Hyalomma dromedarii. Peptide spectra were assigned to taxa using a two-step database search strategy based on NCBInr, and bacterial composition and relative abundance were compared across tick species and sampling locations. A total of 40 bacterial genera belonging to 32 families and four phyla were identified. Microbiome composition differed significantly between tick genera and collection locations, suggesting an influence of species-specific and geographical factors on microbial community structure. Dominant genera included Streptomyces, Bacillus, Clostridium, Escherichia, Flavobacterium, Paenibacillus, and Providencia. Peptides related to Coxiella spp. were frequently detected, consistent with previous reports of Coxiella-like endosymbionts in ticks. This pilot study provides a first metaproteomic characterization of tick-associated communities in Algeria. The results reveal species- and location-associated differences in microbial composition and highlight the potential of metaproteomics for exploring tick-associated microbiomes in North Africa.

Animals↗

PubMed1996

Characterization of Bacterial Communities from Activated Sludge: Culture-Dependent Numerical Identification Versus In Situ Identification Using Group- and Genus-Specific rRNA-Targeted Oligonucleotide Probes

The structures of bacterial communities were studied in activated sludge samples obtained from the aerobic and anaerobic zones of a wastewater treatment plant showing enhanced phosphorous removal. Samples were analyzed by in situ hybridization with oligonucleotide probes complementary to selected regions of the 16S and 23S ribosomal RNA (rRNA) characteristic for defined phylogenetic entities (genera and larger groups). The microbial community structures revealed by molecular techniques were compared with the compositions of culturable bacterial communities, obtained from the characterization of 255 isolates from tryptone-soy (TS) agar and R2A agar. These isolates were characterized by 89 physiological tests and their cellular fatty acid patterns, and identified. Culture-dependent techniques indicated the following distribution: different Aeromonas spp. (2.7-8.3% on R2A agar; 45.0-63.7% on TS agar), Acinetobacter spp. (5.4-9.0% on R2A agar; 5.0-9.1% on TS agar), Pseudomonas spp. (up to 10% on R2A agar) and Shewanella putrefaciens (up to 3.0% on R2A agar), all members of the gamma subclass of Proteobacteria, were isolated most frequently. The relatively rare isolates of the beta subclass were identified as Acidovorax spp., Alcaligenes spp., and Comamonas spp.. The Gram-positive bacteria (high DNA G+C) were assigned mainly to Arthrobacter spp., Microbacterium spp., and Mycobacterium phlei. In order to assess the in situ abundance of the most frequently isolated genus, Aeromonas, two rRNA-targeted oligonucleotide probes were developed. The two gamma proteobacterial genera Aeromonas and Acinetobacter constituted less than 5% of all bacteria. In situ, Proteobacteria belonging to the beta subclass and high G+C Gram-positive bacteria were dominant. From filamentous bacteria, Sphaerotilus spp. and Leptothrix spp. could be detected occasionally. In addition, one sample contained a high proportion of the morphologically distinct filaments of Microthrix parvicella.

Journal Article↗

PubMed2025

Metagenomic analysis reveals global landscape of viruses in biogeochemical cycles and microbial resistance in paddy soils and wetlands.

Paddy soils and wetlands form a critical soil-water interface that supports global crop production and biogeochemical cycling. Understanding the role of viruses in these ecosystems is vital for predicting ecosystem resilience. Considering the significance of viruses in microbial community structure and environmental pollution, we analyzed 163 metagenomes from 18 countries in Asia, Europe, America, and Australia. We characterized the global distribution and potential ecological functions of viruses through viral auxiliary metabolic genes (vAMGs), antibiotic resistance genes (vARGs), and metal(loid) resistance genes (vMRGs). We found viruses with globally consistent compositions and host profiles, characterized by high richness and a dominance of lysogenic families. We identified 497 vAMGs associated with carbon, phosphorus, nitrogen, and sulfur cycling, and detected 279 vARGs (conferring resistance to 10 antibiotic) and 141 vMRGs (against 7 metal(loids)). These genes exhibited strong co-localization and co-selection patterns, and their transduction can promote the emergence of multi-resistant microbes, reshaping microbial communities. Therefore, viruses are key mobile vectors for the environmental spread of these genes. By quantifying these pathways, we provide a crucial advancement for ecological risk identification and assessment. This meta-analysis provides a comprehensive overview of virus-mediated biogeochemical processes and resistance gene propagation. We demonstrate that viruses can disseminate antibiotic and metal(loid) resistance, a pollution-driven process that poses potential health risks. Furthermore, by regulating key metabolic pathways, viruses can influence greenhouse gas fluxes. Our findings underscore the necessity of integrating viruses into climate models, pollution mitigation strategies, and One Health policies to assess ecological risks and to protect ecosystem and public health.

Wetlands↗

PubMed2001

Characterization of microbial community in an activated sludge process treating domestic wastewater using quinone profiles.

The dynamics of microbial community structure of activated sludges in a small-scale domestic wastewater treatment process were examined using a novel approach of quinone profiles. The composition and content of quinones in the activated sludges were analyzed monthly over a period of one year. More than 4 types of ubiquinones and 12 types of menaquinones were observed in the activated sludges, with the dominant quinones being ubiquinone (UQ)-8, menaquinone (MK)-7, followed by UQ-10, MK-8 and MK-6. The total quinone contents in the activated sludges varied from 0.93 to 2.68 mumol per gram of particle organic carbon. The molar ratio of ubiquinones to menaquinones (UK/MK) changed from 0.38 to 0.98, indicating that anaerobic bacteria dominated the microbial community of the activated sludges examined. The ratio of UQ/MK varied similar to that of dissolved oxygen in the bulk. The microbial diversity of the activated sludges calculated from the quinone compositions was 13.4-16.8. The diversity of menaquinones was much higher than that of ubiquinones, and increased slightly with increasing temperature. The microorganisms containing menaquinones appear to be sensitive to the change in temperature than those containing ubiquinones.

Bacteria↗

PubMed2002

The filamentation pathway controlled by the Efg1 regulator protein is required for normal biofilm formation and development in Candida albicans.

Candida albicans biofilms are structured microbial communities composed of a mixture of yeast cells and hyphal elements, suggesting a pivotal role for the dimorphic switch in the development of biofilms. We have used C. albicans mutants defective in genes involved in filamentation (Deltacph1, Deltaefg1, Deltahst7, and Deltacst20) and compared these mutants to wild-type strains to determine whether filamentation is an integral factor for biofilm formation. Scanning electron microscopy revealed that Deltacph1, Deltahst7 and Deltacst20 mutants were able to filament and form structured biofilms displaying three-dimensional architecture similar to those formed by wild-type strains. However, Deltaefg1 and Deltacph1/Deltaefg1 mutants were unable to filament and did not form biofilms, but rather sparse monolayers of loosely attached elongated, rod-like, cells. Antimicrobial susceptibility testing showed intrinsic resistance of all mutant strains to fluconazole and amphotericin B when attached to the surface of biomaterials. These results suggest that hyphal formation is pivotal for biofilm development in C. albicans. However, the sessile lifestyle associated with adherent cells confers antifungal resistance, regardless of coherent biofilm formation.

Amphotericin B↗

PubMed2004

A shallow BTEX and MTBE contaminated aquifer supports a diverse microbial community.

Microbial communities in subsurface environments are poorly characterized and the impacts of anthropogenic contamination on their structure and function have not been adequately addressed. The release of contaminant(s) to a previously unexposed environment is often hypothesized to decrease the diversity of the affected community. We characterized the structure of microbial communities along a gradient of benzene, toluene, ethylbenzene, and xylene (BTEX) and methyl-tert-butyl-ether (MTBE) contamination, resulting from a petroleum spill, within a shallow sandy aquifer at Vandenberg Air Force Base (VAFB) in Lompoc, CA. Differences in microbial community composition along the contaminant plume were assessed via a combinatorial approach utilizing denaturing gradient gel electrophoresis (DGGE), cloning and sequencing, intergenic transcribed spacer analysis (ITS), and comparative phylogenetic analysis of partial 16S rDNA sequences. Substantial bacterial sequence diversity, similar levels of species richness, and similar phylo-groups (including the Cytophaga-Flavobacterium-Bacteroidetes group and numerous members of the alpha-, beta-, gamma-, delta-, and epsilon-groups of the proteobacteria) were observed in both uncontaminated and contaminated regions of the aquifer. High-resolution measures (ITS fingerprinting and phylogenetic inference) readily separated communities impacted by the original petroleum spill (in source zone) from those in other parts of the aquifer and indicated that communities exposed to MTBE only were similar to communities in uncontaminated regions. Collectively, these data suggest that petroleum contamination alters microbial community structure at the species and subspecies level. Further study is required to determine whether these changes have an impact on the functioning of this subsurface ecosystem.

Bacteria↗

PubMed2004

Archaeal community structure and pathway of methane formation on rice roots.

The community structure of methanogenic Archaea on anoxically incubated rice roots was investigated by amplification, sequencing, and phylogenetic analysis of 16S rRNA and methyl-coenzyme M reductase (mcrA) genes. Both genes demonstrated the presence of Methanomicrobiaceae, Methanobacteriaceae, Methanosarcinaceae, Methanosaetaceae, and Rice cluster I, an uncultured methanogenic lineage. The pathway of CH4 formation was determined from the 13C-isotopic signatures of the produced CH4, CO2 and acetate. Conditions and duration of incubation clearly affected the methanogenic community structure and the pathway of CH4 formation. Methane was initially produced from reduction of CO2 exclusively, resulting in accumulation of millimolar concentrations of acetate. Simultaneously, the relative abundance of the acetoclastic methanogens (Methanosarcinaceae, Methanosaetaceae), as determined by T-RFLP analysis of 16S rRNA genes, was low during the initial phase of CH4 production. Later on, however, acetate was converted to CH4 so that about 40% of the produced CH4 originated from acetate. Most striking was the observed relative increase of a population of Methanosarcina spp. (but not of Methanosaeta spp.) briefly before acetate concentrations started to decrease. Both acetoclastic methanogenesis and Methanosarcina populations were suppressed by high phosphate concentrations, as observed under application of different buffer systems. Our results demonstrate the parallel change of microbial community structure and function in a complex environment, i.e., the increase of acetoclastic Methanosarcina spp. when high acetate concentrations become available.

Acetates↗

PubMedDate not supplied

Soil microbial communities associated with Bt and non-Bt corn in three soils.

The effects of expression of Cry endotoxin by Bt corn (transgenic corn engineered to express Bacillus thuringiensis toxin) on soil microbial community structure were assessed in a growth chamber experiment. Two lines of transgenic corn expressing different Cry endotoxins were compared with their respective non-transgenic isolines in three soil types with differing textures. Phospholipid fatty acid (PLFA) profiles from bulk soil and community-level physiological profiles (CLPP) from the rhizosphere community were used to assess community structure. Differences in PLFA profiles due to soil type were significant, accounting for 73% of the total variability in the dataset. Differences in bacterial and fungal CLPP profiles due to soil type were statistically significant, but probably not biologically important, accounting for 6.3 and 3.8% of the total variability, respectively. Neither expression of Cry endotoxin nor corn line had a significant effect on microbial profiles, except in the high-clay soil where both factors significantly affected bacterial CLPP profiles (accounting for 6.6 and 6.1% of the variability in that soil, respectively). Expression of Cry endotoxin also significantly reduced the presence of eukaryotic PLFA biomarker in bulk soils, although it is unclear which groups of eukaryotes were affected. We conclude that the effects of transgenic Bt corn in this short-term experiment are small, and longer-term investigations are necessary.

Aluminum Silicates↗

PubMed2004

Effects of gamma irradiation on Holcus lanatus (Yorkshire fog grass) and associated soil microorganisms.

An investigation was conducted to determine the impact of acute doses of gamma radiation on the microbial community structure of a Holcus lanatus dominated grassland soil. Mesocosms containing soil and established grass were irradiated using a sealed (137)Cs source (7.0 Gy min(-1)). Doses ranged from 5 to 160 Gy, analyses were conducted on the day of irradiation, then 7 and 30 days later. Plant growth and arbuscular mycorrhizal fungal colonisation of roots were reduced by irradiation. Gram-negative bacteria, and microbial metabolic capacity were also negatively affected by treatment. Microbial biomass measured by phospholipid fatty acid (PLFA) analysis, showed an increase at doses above 20 Gy, 7 and 30 days after treatment. Proportions of Gram-positive bacterial and fungal PLFAs fluctuated inversely to each other, in response to both sampling time and radiation dose. We hypothesise that many of the observed soil microbial responses are indirect effects mediated by the influence of ionising radiation on the plants in this system.

Fungi↗

PubMed2000

Microflora of technogenous wastes characterised by fatty acid profiling.

Fatty acid methyl ester (FAME) profiles obtained directly in situ have been used to estimate microbial community structure in different technogenous wastes. The effect of nutrients added, simulating the effect of plant-derived exudates on the indigenous microflora in the heaps during the reclamation process, was also studied in microcosms. The wastes such as coal-mine spoil, non-ferrous metallurgical slag and coal fly-ash were characterised by a poorly developed microflora as compared to a typical sandy loam soil. However, the most similar to the soil was the community structure in the coalmine spoil. The high content of 18: 2omega6,9 found in the metallurgical slag indicated the domination of fungi in this waste. In contrast, representatives of the Cytophaga-Flavobacterium group dominated the coal fly-ash, for which 16:1omega5c was used as the marker acid. The waste amendment resulted in changes of FAME profiles obtained. However, the changes were site-specific, indicating response of particular microbial groups to the added nutrients.

Ecology↗