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Active Microbial Populations (active + microbial_population)
Selected AbstractsField-scale 13C-labeling of phospholipid fatty acids (PLFA) and dissolved inorganic carbon: tracing acetate assimilation and mineralization in a petroleum hydrocarbon-contaminated aquiferFEMS MICROBIOLOGY ECOLOGY, Issue 3 2002Silvina A. Pombo Abstract This study was conducted to determine the feasibility of labeling phospholipid-derived fatty acids (PLFA) of an active microbial population with a 13C-labeled organic substrate in the denitrifying zone of a petroleum hydrocarbon-contaminated aquifer during a single-well push-pull test. Anoxic test solution was prepared from 500 l of groundwater with addition of 0.5 mM Br, as a conservative tracer, 0.5 mM NO3,, and 0.25 mM [2- 13C]acetate. At 4, 23 and 46 h after injection, 1000 l of test solution/groundwater mixture were sequentially extracted. During injection and extraction phases we measured Br,, NO3, and acetate concentrations, characterized the microbial community structure by PLFA and fluorescent in situ hybridization (FISH) analyses, and determined 13C/12C ratios in dissolved inorganic carbon (DIC) and PLFA. Computed first-order rate coefficients were 0.63±0.08 day,1 for NO3, and 0.70±0.05 day,1 for acetate consumption. Significant 13C incorporation in DIC and PLFA was detected as early as 4 h after injection. At 46 h we measured ,13C values of up to 5614, in certain PLFA (especially monounsaturated fatty acids), and up to 59.8, in extracted DIC. Profiles of enriched PLFA and FISH analysis suggested the presence of active denitrifiers. Our results demonstrate the applicability of 13C labeling of PLFA and DIC in combination with FISH to link microbial structure and activities at the field scale during a push-pull test. [source] Prokaryotic diversity and metabolically active microbial populations in sediments from an active mud volcano in the Gulf of MexicoENVIRONMENTAL MICROBIOLOGY, Issue 10 2006Robert J. Martinez Summary In this study, ribosomes and genomic DNA were extracted from three sediment depths (0,2, 6,8 and 10,12 cm) to determine the vertical changes in the microbial community composition and identify metabolically active microbial populations in sediments obtained from an active seafloor mud volcano site in the northern Gulf of Mexico. Domain-specific Bacteria and Archaea 16S polymerase chain reaction primers were used to amplify 16S rDNA gene sequences from extracted DNA. Complementary 16S ribosomal DNA (crDNA) was obtained from rRNA extracted from each sediment depth that had been subjected to reverse transcription polymerase chain reaction amplification. Twelve different 16S clone libraries, representing the three sediment depths, were constructed and a total of 154 rDNA (DNA-derived) and 142 crDNA (RNA-derived) Bacteria clones and 134 rDNA and 146 crDNA Archaea clones obtained. Analyses of the 576 clones revealed distinct differences in the composition and patterns of metabolically active microbial phylotypes relative to sediment depth. For example, ,- Proteobacteria rDNA clones dominated the 0,2 cm clone library whereas ,-Proteobacteria dominated the 0,2 cm crDNA library suggesting , to be among the most active in situ populations detected at 0,2 cm. Some microbial lineages, although detected at a frequency as high as 9% or greater in the total DNA library (i.e. Actinobacteria, ,- Proteobacteria), were markedly absent from the RNA-derived libraries suggesting a lack of in situ activity at any depth in the mud volcano sediments. This study is one of the first to report the composition of the microbial assemblages and physiologically active members of archaeal and bacterial populations extant in a Gulf of Mexico submarine mud volcano. [source] Microbial community dynamics in nutrient-pulsed chemostatsFEMS MICROBIOLOGY ECOLOGY, Issue 1 2006Militza Carrero-Colón Abstract In nature, microbes are subject to nutrient fluxes. As the periodicity of nutrient flux lengthens, different physiological traits may be selected. The competitive exclusion principle stipulates that one organism will dominate these systems; however, interspecies interactions may produce a dynamic microbial community. These issues were investigated in chemostats pulsed with gelatin. Chemostats were run over 30 days with substrate addition continuously or at intervals of 0.5, 1 or 3 days. Growth rates were similar between pulse intervals. Ectoaminopeptidase activity levels remained relatively constant within a pulse interval. Bacterial community structure was monitored using denaturing gradient gel electrophoresis of PCR products of the 16S rRNA gene. There were dynamic changes at all periodicities; however, the pace of these changes decreased over time. Final communities were not identical between different treatments. The structure of persistent vs. active microbial populations was compared by denaturing gradient gel electrophoresis of the PCR and reverse transcriptase-PCR amplicons of 16S rDNA and rRNA templates, respectively. For all the chemostats, the rRNA profiles were not identical to the rDNA profiles for a sample. These experiments demonstrate that complex community dynamics can occur under environmental heterogeneities that are modest relative to those found in natural aquatic habitats. Furthermore, the physiological functionality of these dynamic communities was stable. [source] INTEGRATED MANAGEMENT OF IN-FIELD, EDGE-OF-FIELD, AND AFTER-FIELD BUFFERS,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 1 2006Seth M. Dabney ABSTRACT: This review summarizes how conservation benefits are maximized when in-field and edge-of-field buffers are integrated with each other and with other conservation practices such as residue management and grade control structures. Buffers improve both surface and subsurface water quality. Soils under permanent buffer vegetation generally have higher organic carbon concentrations, higher infiltration capacities, and more active microbial populations than similar soils under annual cropping. Sediment can be trapped with rather narrow buffers, but extensive buffers are better at transforming dissolved pollutants. Buffers improve surface runoff water quality most efficiently when flows through them are slow, shallow, and diffuse. Vegetative barriers - narrow strips of dense, erect grass - can slow and spread concentrated runoff. Subsurface processing is best on shallow soils that provide increased hydrologic contact between the ground water plume and buffer vegetation. Vegetated ditches and constructed wetlands can act as "after-field" conservation buffers, processing pollutants that escape from fields. For these buffers to function efficiently, it is critical that in-field and edge-of-field practices limit peak runoff rate and sediment yield in order to maximize contact time with buffer vegetation and minimize the need for cleanout excavation that destroys vegetation and its processing capacity. [source] | ||||||||||