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Anoxic Zone (anoxic + zone)
Selected AbstractsDetection of microbial biomass by intact polar membrane lipid analysis in the water column and surface sediments of the Black SeaENVIRONMENTAL MICROBIOLOGY, Issue 10 2009Florence Schubotz Summary The stratified water column of the Black Sea produces a vertical succession of redox zones, stimulating microbial activity at the interfaces. Our study of intact polar membrane lipids (IPLs) in suspended particulate matter and sediments highlights their potential as biomarkers for assessing the taxonomic composition of live microbial biomass. Intact polar membrane lipids in oxic waters above the chemocline represent contributions of bacterial and eukaryotic photosynthetic algae, while anoxygenic phototrophic bacteria and sulfate-reducing bacteria comprise a substantial amount of microbial biomass in deeper suboxic and anoxic layers. Intact polar membrane lipids such as betaine lipids and glycosidic ceramides suggest unspecified anaerobic bacteria in the anoxic zone. Distributions of polar head groups and core lipids show planktonic archaea below the oxic zone; methanotrophic archaea are only a minor fraction of archaeal biomass in the anoxic zone, contrasting previous observations based on the apolar derivatives of archaeal lipids. Sediments contain algal and bacterial IPLs from the water column, but transport to the sediment is selective; bacterial and archaeal IPLs are also produced within the sediments. Intact polar membrane lipid distributions in the Black Sea are stratified in accordance with geochemical profiles and provide information on vertical successions of major microbial groups contributing to suspended biomass. This study vastly extends our knowledge of the distribution of complex microbial lipids in the ocean. [source] Substrate incorporation patterns of bacterioplankton populations in stratified and mixed waters of a humic lakeENVIRONMENTAL MICROBIOLOGY, Issue 7 2009Ulrike Buck Summary Bacterial incorporation of glucose, leucine, acetate and 4-hydroxybenzoic acid (HBA) was investigated in an artificially divided humic lake (Grosse Fuchskuhle, Germany). Two basins with contrasting influx of allochthonous organic carbon were sampled during late summer stratification (oxic and anoxic layers) and after autumn mixing. High total and cell-specific incorporation rates were observed for glucose and HBA in stratified and mixed waters respectively, but only a small fraction of bacteria visibly incorporated HBA. The oxic layer of the more humic-rich basin featured a significantly lower fraction of glucose incorporating cells and substantially higher proportions of acetate assimilating bacteria. Niche differentiation was observed in two betaproteobacterial populations: cells affiliated with the Polynucleobacter C subcluster efficiently incorporated acetate but little glucose, whereas the opposite was found for members of the R-BT065 clade. By contrast, leucine incorporation was variable in both taxa. Considering the high concentrations and rapid photochemical generation of organic acids in humic waters our results may help to explain the success of the Polynucleobacter C lineage in such habitats. Specific substrate or habitat preferences were also present in three subgroups of the actinobacterial acI lineage: The numerically dominant clade in oxic waters (acI-840-1) was absent in the anoxic zone and did not incorporate acetate. A second group (acI-840-2) was found both in the epi- and hypolimnion, whereas the third one (acI-840-3) only occurred in anoxic waters. Altogether our results suggest a constitutive preference for some substrates versus an adaptive utilization of others in the studied microbial groups. [source] Transcriptional activity of paddy soil bacterial communitiesENVIRONMENTAL MICROBIOLOGY, Issue 4 2009Pravin Malla Shrestha Summary Bulk mRNA was used to explore the transcriptional activity of bacterial communities in oxic versus anoxic paddy soil. Two microbial cDNA libraries were constructed from composite samples using semi-randomly primed RT-PCR. cDNAs averaged 500,600 bp in length and were treated as expressed sequence tags (ESTs). Clustering analysis of 805 random cDNAs resulted in 179 and 155 different ESTs for the oxic and anoxic zones respectively. Using an E -value threshold of e,10, a total of 218 different ESTs could be assigned by blastx, while 116 ESTs were predicted novel. Both the proportion and significance of the EST assignments increased with cDNA length. Taxonomic assignment was more powerful in discriminating between the aerobic and anaerobic bacterial communities than functional inference, as most ESTs in both oxygen zones were putative indicators of similar housekeeping functions, in particular ABC-type transporters. A few ESTs were putative indicators for community function in a biogeochemical context, such as ,-oxidation of long-chain fatty acids specifically in the oxic zone. Expressed sequence tags assigned to Alpha- and Betaproteobacteria were predominantly found in the oxic zone, while those affiliated with Deltaproteobacteria were more frequently detected in the anoxic zone. At the genus level, multiple assignments to Bradyrhizobium and Geobacter were unique to the oxic and anoxic zones respectively. The phylum-level affiliations of 93 16S rRNA sequences corresponded well with two taxonomically distinct EST patterns. Expressed sequence tags affiliated with Acidobacteria and Chloroflexi were frequently detected in both oxygen zones. In summary, the soil metatranscriptome is accessible for global analysis and such studies have great potential in elucidating the taxonomic and functional status of soil bacterial communities, but study significance depends on the number and length of cDNAs being randomly analysed. [source] Dominance of a clonal green sulfur bacterial population in a stratified lakeFEMS MICROBIOLOGY ECOLOGY, Issue 1 2009Lea H. Gregersen Abstract For many years, the chemocline of the meromictic Lake Cadagno, Switzerland, was dominated by purple sulfur bacteria. However, following a major community shift in recent years, green sulfur bacteria (GSB) have come to dominate. We investigated this community by performing microbial diversity surveys using FISH cell counting and population multilocus sequence typing [clone library sequence analysis of the small subunit (SSU) rRNA locus and two loci involved in photosynthesis in GSB: fmoA and csmCA]. All bacterial populations clearly stratified according to water column chemistry. The GSB population peaked in the chemocline (c. 8 × 106 GSB cells mL,1) and constituted about 50% of all cells in the anoxic zones of the water column. At least 99.5% of these GSB cells had SSU rRNA, fmoA, and csmCA sequences essentially identical to that of the previously isolated and genome-sequenced GSB Chlorobium clathratiforme strain BU-1 (DSM 5477). This ribotype was not detected in Lake Cadagno before the bloom of GSB. These observations suggest that the C. clathratiforme population that has stabilized in Lake Cadagno is clonal. We speculate that such a clonal bloom could be caused by environmental disturbance, mutational adaptation, or invasion. [source] Transport and distribution of lindane and simazine in a riverine environment: measurements in bed sediments and modellingPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 5 2004Ian J Allan Abstract Aquatic sediments often remove hydrophobic contaminants from fresh waters. The subsequent distribution and concentration of contaminants in bed sediments determines their effect on benthic organisms and the risk of re-entry into the water and/or leaching to groundwater. This study examines the transport of simazine and lindane in aquatic bed sediments with the aim of understanding the processes that determine their depth distribution. Experiments in flume channels (water flow of 10 cm s,1) determined the persistence of the compounds in the absence of sediment with (a) de-ionised water and (b) a solution that had been in contact with river sediment. In further experiments with river bed sediments in light and dark conditions, measurements were made of the concentration of the compounds in the overlying water and the development of bacterial/algal biofilms and bioturbation activity. At the end of the experiments, concentrations in sediments and associated pore waters were determined in sections of the sediment at 1 mm resolution down to 5 mm and then at 10 mm resolution to 50 mm depth and these distributions analysed using a sorption,diffusion,degradation model. The fine resolution in the depth profile permitted the detection of a maximum in the concentration of the compounds in the pore water near the surface, whereas concentrations in the sediment increased to a maximum at the surface itself. Experimental distribution coefficients determined from the pore water and sediment concentrations indicated a gradient with depth that was partly explained by an increase in organic matter content and specific surface area of the solids near the interface. The modelling showed that degradation of lindane within the sediment was necessary to explain the concentration profiles, with the optimum agreement between the measured and theoretical profiles obtained with differential degradation in the oxic and anoxic zones. The compounds penetrated to a depth of 40,50 mm over a period of 42 days. Copyright © 2004 Society of Chemical Industry [source] | ||||||||||