Search results for "Bacteria"
showing 10 items of 4919 documents
Determinants of the distribution of nitrogen-cycling microbial communities at the landscape-scale
2010
Little information is available regarding the landscape-scale distribution of microbial communities and its environmental determinants. However, a landscape perspective is needed to understand the relative importance of local and regional factors and land management for the microbial communities. In this manuscript, we investigated the distribution of functional microbial communities involved in N-cycling and of the total bacterial and crenarchaeal communities over 107 sites using a grid with a 16 km lag distance within Burgundy, a 31 500 km2 region in France. After quantifying the abundances of the total bacterial, crenarchaeal, nitrate-reducing, denitrifying and ammonia-oxidizing communit…
Effect of cropping cycles and repeated herbicide applications on the degradation of diclofop-methyl, bentazone, diuron, isoproturon and pendimethalin…
2002
A greenhouse study was conducted to investigate the ability of four crops (wheat, corn, oilseed rape and soybean) to influence the degradation of bentazone, diclofop-methyl, diuron, isoproturon and pendimethalin in soil. The present study showed that microbial biomass-carbon was significantly higher in planted soils than in bulk soil, especially with wheat and corn, after several cropping cycles. The biomass in corn and soybean planted soils was adversely affected by bentazone but recovered after three cropping cycles. In wheat-planted soils, diclofop-methyl application resulted in persistent increase of the amount of microbial biomass. Bentazone did not show accelerated degradation even af…
Monitoring of atrazine treatment on soil bacterial, fungal and atrazine-degrading communities by quantitative competitive PCR
2003
We report the development of quantitative competitive (QC) PCR assays for quantifying the 16S, 18S ribosomal and atzC genes in nucleic acids directly extracted from soil. QC-PCR assays were standardised, calibrated and evaluated with an experimental study aiming to evaluate the impact of atrazine application on soil microflora. Comparison of QC-PCR 16S and 18S results with those of soil microbial biomass showed that, following atrazine application, the microbial biomass was not affected and that the amount of 16S rDNA gene representing 'bacteria' increased transitorily, while the amount of 18S rDNA gene representing fungi decreased in soil. In addition, comparison of atzC QC-PCR results wit…
Evaluation agroécologique de systèmes de culture en zone tropicale humide : Cas de la mise en valeur agricole d'une savane herbacée acide (Plaine des…
2013
Dans les régions tropicales humides, concilier intensification agricole et protection des ressources naturelles est un défi majeur et difficile à relever. Dans les savanes acides du nord-est laotien, des systèmes de culture de semis direct sur couverture végétale (SCV), basés sur les trois principes du non-labour, d’une couverture permanente du sol, et sur la pratique de rotations culturales diversifiées, sont proposés comme alternative technique à l’intensification agricole conventionnelle basée sur le labour. Si ces systèmes ont connu une diffusion importante et rapide dans les grandes agricultures mécanisées, leur diffusion reste néanmoins à ce jour limitée en contexte de petite agricult…
Seasonal dynamics of the bacterial community in forest soils under different quantities of leaf litter
2010
International audience; Soil microbial communities play an important role in soil carbon functioning, particularly in forest ecosystems. Their variation in response to climate change may affect soil carbon processes, highlighting the importance of understanding how environmental factors affect microbial communities. This study aimed to determine to what extent an increase in the quantity of fresh litter may affect heterotrophic mineralization of organic carbon and bacterial community structure in soil and litter. A litter manipulation experiment was performed in situ in a temperate deciduous forest. Three treatments of fresh litter inputs were considered: litter exclusion, natural condition…
Characterization of a novel selenium methyltransferase from freshwater bacteria showing strong similarities with the calicheamicin methyltransferase
2004
A novel group of Se-methyltransferases is presented. The genetic determinant, named mmtA, which revealed this group was isolated from selenite and selenate-resistant freshwater bacteria. E. coli expressing mmtA and grown with a Se supplement emitted dimethyl selenide (DMSe) and dimethyl diselenide (DMDSe). Phylogenetic analysis divided MmtA-like bacterial sequences into two clusters, one grouping MmtA with S- and O-methyltransferases, and one grouping UbiE C-methyltransferases. Se methylation by some of these MmtA phyletic neighbours was investigated.
Differential Responses of Nitrate Reducer Community Size, Structure, and Activity to Tillage Systems
2009
ABSTRACT The main objective of this study was to determine how the size, structure, and activity of the nitrate reducer community were affected by adoption of a conservative tillage system as an alternative to conventional tillage. The experimental field, established in Madagascar in 1991, consists of plots subjected to conventional tillage or direct-seeding mulch-based cropping systems (DM), both amended with three different fertilization regimes. Comparisons of size, structure, and activity of the nitrate reducer community in samples collected from the top layer in 2005 and 2006 revealed that all characteristics of this functional community were affected by the tillage system, with increa…
Copper Dynamics and Impact on Microbial Communities in Soils of Variable Organic Status
2008
International audience; The effect of soil organic status on copper impact was investigated by means of a microcosm study carried out on a vineyard soil that had been amended with varying types of organic matter during a previous long-term field experiment. Soil microcosms were contaminated at 250 mg Cu kg−1 and incubated for 35 days. Copper distribution and dynamics were assessed in the solid matrix by a sequential extraction procedure and in the soil solution by measuring total and free exchangeable copper concentrations. Copper bioavailability was also measured with a whole-cell biosensor. Modifications of microbial communities were assessed by means of biomass-C measurements and charact…
Combining ecophysiological and microbial ecological approaches to assess interaction between genotypes of Medicago truncatula and the soil bacterial …
2011
International audience; Microbial communities can play a key role in sustainable agriculture by improving crop growth. Currently, a major stake is to study the effect of the plant genotype on the shaping of the soil microbial communities in relation to the plant nutrition. Methods: The links between the plant genotype and the rhizospheric bacterial communities were assessed at both structural and functional level using a multidisciplinary approach. On the one side, the genetic structure (Automated Ribosomial Intergenic Spacer Analysis (ARISA)) and diversity (454 pyrosequencing) of bacterial communities of the rhizosphere was first analysed. On the other side, using an ecophysiological model…
Relationships between Staphylococcus aureus genetic background, virulence factors, agr groups (alleles), and human disease
2002
ABSTRACT The expression of most Staphylococcus aureus virulence factors is controlled by the agr locus, which encodes a two-component signaling pathway whose activating ligand is an agr -encoded autoinducing peptide (AIP). A polymorphism in the amino acid sequence of the AIP and of its corresponding receptor divides S. aureus strains into four major groups. Within a given group, each strain produces a peptide that can activate the agr response in the other member strains, whereas the AIPs belonging to different groups are usually mutually inhibitory. We investigated a possible relationship between agr groups and human S. aureus disease by studying 198 S. aureus strains isolated from 14 asym…