A Defined Terminal Region of the E. coli Chromosome Shows Late Segregation and High FtsK Activity

Background: The FtsK DNA-translocase controls the last steps of chromosome segregation in E. coli. It translocates sister chromosomes using the KOPS DNA motifs to orient its activity, and controls the resolution of dimeric forms of sister chromosomes by XerCD-mediated recombination at the dif site and their decatenation by TopoIV. Methodology: We have used XerCD/dif recombination as a genetic trap to probe the interaction of FtsK with loci located in different regions of the chromosome. This assay revealed that the activity of FtsK is restricted to a,400 kb terminal region of the chromosome around the natural position of the dif site. Preferential interaction with this region required the tethering of FtsK to the division septum via its N-terminal domain as well as its translocation activity. However, the KOPSrecognition activity of FtsK was not required. Displacement of replication termination outside the FtsK high activity region had no effect on FtsK activity and deletion of a part of this region was not compensated by its extension to neighbouring regions. By observing the fate of fluorescent-tagged loci of the ter region, we found that segregation of the FtsK high activity region is delayed compared to that of its adjacent regions. Significance: Our results show that a restricted terminal region of the chromosome is specifically dedicated to the last step

Rôles de la translocase FtsK dans la ségrégation du chromosome chez Escherichia coli

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Preliminary metabolomic approach on the bacterial structure community of Haslea ostrearia

The marine diatom Haslea ostrearia [1] produces a water-soluble blue-pigment named marennine [2] of economic interest. But the lack of knowledge of the ecological conditions, under which this microalga develops in its natural ecosystem, more especially bacteria H. ostrearia interactions, prevents any optimization of its culture in well-controlled conditions. The structure of the bacterial community was analyzed by PCR-TTGE before and after the isolation of H. ostrearia cells recovered from 4 localities, to distinguish the relative part of the biotope and the biocenose and eventually to describe the temporal dynamic of the structure of the bacterial community at two time-scales. The differences in genetic fingerprints, more especially high between two H. ostrearia isolates (HO-R and HO-BM) showed also the highest differences in the bacterial structure [3] as the result of specific metabolomics profiles. The non-targeted metabolomic investigation showed that these profiles were more distinct in case of bacteria-alga associations than for the H. ostrearia monoculture Here we present a Q-TOF LC/MS metabolomic fingerprinting approach [3]: - to investigate differential metabolites of axenic versus non axenic H. ostrearia cultures. - to focus on the specific metabolites of a bacterial surrounding associated with the activation or inhibition of the microalga growing. The Agilent suite of data processing software makes feature finding, statistical analysis, and identification easier. This enables rapid transformation of complex raw data into biologically relevant metabolite information

Isolation and screening of indigenous bacteria from phosphogypsum-contaminated soils for their potential in promoting plant growth and trace elements mobilization

International audienceBacteria isolated from soils in the vicinity of phosphogypsum (PG) stockpiles were studied for their potential use in bioaugmentation-assisted phytoextraction. Quick, miniaturized biochemical tests were performed in the presence of metal trace elements (MTE), including rare earth elements (Cd, Sr, Ce, La, Nd and Y), corresponding to their bioavailable concentrations in PG. The intention herein was to assess the capacity of bacteria to: i) grow in PG; ii) produce indole acetic acid and ACC deaminase to promote plant growth and reduce stress; and iii) produce siderophores, including pyoverdine, to mobilize MTE. Results showed that even at maximum PG concentration (10 g/L and pH 3.40), 7 out of 32 isolates were able to grow. The biochemical tests showed differences in the presence or absence of MTE. The presence of MTE seems to promote the production of IAA by a factor of 3.25. On the contrary, it inhibits ACC deaminase and siderophore production, including pyoverdine. According to a scoring method applied, the two most efficient isolates exhibiting maximum metabolite production were identified as Bacillus sp

Fate and transport of metal trace elements from phosphogypsum piles in Tunisia and their impact on soil bacteria and wild plants

International audienc

A dual role for the FtsK protein in Escherichia coli chromosome segregation

FtsK is a multifunctional protein that acts in Escherichia coli cell division and chromosome segregation. Its C-terminal domain is required for XerCD-mediated recombination between dif sites that resolve chromosome dimers formed by recombination between sister chromosomes. We report the construction and analysis of a set of strains carrying different Xer recombination sites in place of dif, some of which recombine in an FtsK-independent manner. The results show that FtsK-independent Xer recombination does not support chromosome dimer resolution. Furthermore, resolution of dimers by the Cre/loxP system also requires FtsK. These findings reveal a second role for FtsK during chromosome dimer resolution in addition to XerCD activation. We propose that FtsK acts to position the dif regions, thus allowing a productive synapse between dif sites

Bacterial community structure of the marine diatom Haslea ostrearia

Haslea ostrearia produces a water-soluble, blue-green pigment, called marennine, with proven economic benefits (as a bioactive compound used to green oysters, which improves their market value). Incomplete knowledge of the ecological features of this marine diatom complicates its cultivation. More specifically, the ecology of bacteria surrounding H. ostrearia in ponds is what remains unknown. The structure of this bacterial community was previously analyzed by means of PCR-TTGE before and after isolating H. ostrearia cells recovered from 4 localities in order to distinguish the relative parts of the biotope and biocenose and to describe the temporal dynamics of the bacterial community structure at two time scales (2 weeks vs. 9 months). The bacterial structure of the phycosphere differed strongly from that of bulk sediment. The level of similarity between bacteria recovered from the biofilm and suspended bacteria did not exceed 10%. On the other hand, similarities among the bacterial community structures in biofilms were above 90% regardless of the geographic origin of the algal isolates, while the percentages were lower for suspended bacteria. The differences in bacterial structures of two H. ostrearia isolates (HO-R and HO-BM) resulted in specific metabolomic profiles. The nontargeted metabolomic investigation revealed more distinct profiles in the case of this bacteria-alga association than for the H. ostrearia monoculture. At the culture cycle scale under laboratory conditions, the bacterial community depended on the growth stage. When H. ostrearia was subcultured for 9 months, a shift in the bacterial structure was observed as of 3 months, with the bacterial structure stabilizing afterwards (70%–86% similarities), in spite of the size reduction of the H. ostrearia frustule. Based on these results, an initial insight into the relationships between H. ostrearia and its surrounding bacteria could be drawn, leading to a better understanding of the ecological feature of this marine diatom

Effect of Pseudomonas putida-producing pyoverdine on copper uptake by Helianthus annuus cultivated on vineyard soils

International audienceBioaugmentation-assisted phytoextraction was used to reduce the Cu load in vineyard soils. While performance is usually the endpoint of such studies, here we identified some mechanisms underlying Cu soil to plant transfer, particularly the role of siderophores in the extraction of Cu from the soil-bearing phases and its phytoavailability.Carbonated vs. non-carbonated vineyard soils were cultivated with sunflower in rhizoboxes bioaugmented with Pseudomonas putida. gfp-Tagged P. putida was monitored in the soil and pyoverdine (Pvd), Cu, Fe, Mn, and Zn were measured in the soil solution. Trace elements (TE) were analysed in the roots and shoots. Plant growth and nutritional status were also measured.With bioaugmentation, the concentration of total Cu (vs. Cu2+) in the soil solution increased (decreased) by a factor of 1.6 to 2.6 (7 to 13) depending on the soil. The almost 1:1 relationship between the excess of Fe + Cu mobilized from the solid phase and the amount of Pvd in the soil solution in bioaugmented treatments suggests that Pvd mobilized Fe and Cu mainly by ligand-controlled dissolution via a 1:1 metal-Pvd complex. Bioaugmentation increased the Cu concentration by 17% in the shoots and by 93% in the roots, and by 30% to 60% the sunflower shoot biomass leading to an increase in the amount of Cu phytoextracted by up to 87%. The amount of Fe, Mn, Zn, and P also increased in the roots and shoots. Contrary to what was expected, carbonated soil did not increase the mobilization of TE.Our results showed that bioaugmentation increased phytoextraction, and its performance can be further improved by promoting the dissociation of Pvd-Cu complex in the solution at the soil-root interface

Structure and activity of spontaneous fungal communities in organic substrates used for soilless crops

International audienceMicrobiological activity in substrates is of considerable concern for stability of the material and control of plant pathogens in the root environment. This study analyzes the structure of spontaneous microbial communities in various organic substrates used for soilless crops. Different wood fibers, coir fibers and peats were incubated in controlled conditions. The activity of indigenous microorganisms was monitored by assessing substrate mineralization (CO2 released by substrates, potential enzymatic activity and lignocellulosic composition). The genetic structure of the fungal communities was analyzed by PCR-TTGE. Behavior was repeatable across different batches. Potential enzymatic activity was poorly correlated to microbial respiration and lignocellulosic composition. Microbial structure was specific to each substrate. The highest microbial specificity was for wood fibers, then coir fibers, and finally peats. Our data indicated that microbial activity strongly depends on substrate origin and manufacturing process. Our results suggest that spontaneous development of microorganisms within a substrate could have specific effects on organic matter evolution and disease control

Structure and activity of spontaneous fungal communities in organic substrates used for soilless crops

International audienceMicrobiological activity in substrates is of considerable concern for stability of the material and control of plant pathogens in the root environment. This study analyzes the structure of spontaneous microbial communities in various organic substrates used for soilless crops. Different wood fibers, coir fibers and peats were incubated in controlled conditions. The activity of indigenous microorganisms was monitored by assessing substrate mineralization (CO2 released by substrates, potential enzymatic activity and lignocellulosic composition). The genetic structure of the fungal communities was analyzed by PCR-TTGE. Behavior was repeatable across different batches. Potential enzymatic activity was poorly correlated to microbial respiration and lignocellulosic composition. Microbial structure was specific to each substrate. The highest microbial specificity was for wood fibers, then coir fibers, and finally peats. Our data indicated that microbial activity strongly depends on substrate origin and manufacturing process. Our results suggest that spontaneous development of microorganisms within a substrate could have specific effects on organic matter evolution and disease control