The LysR-type regulator SftR is involved in soil survival and sulphate ester metabolism in Pseudomonas putida.

Sulphate esters make up a large proportion of the available sulphur in agricultural soils, and many pseudomonads can desulphurize a range of aryl- and alkylsulphate esters to provide sulphur for growth. After miniTn5 transposon mutagenesis of Pseudomonas putida S-313, we isolated 19 mutants that were defective in cleavage of the chromogenic sulphate ester 5-bromo-4-chloro-3-indoxylsulphate (X-sulphate). Analysis of these strains revealed that they carried independent insertions in a gene cluster that comprised genes for a sulphate ester/sulphonate transporter (atsRBC) a LysR-type regulator (sftR), an oxygenolytic alkylsulphatase (atsK), an arylsulphotransferase (astA) and a putative TonB-dependent receptor (sftP). The SftP protein was localized in the outer membrane, and the arylsulfphotransferase was identified as an intracellular enzyme. Expression of sftR was repressed in the presence of inorganic sulphate, and the sftR gene was required for the expression of atsBC, atsRK and sftP-astA. An sftR mutant was unable to grow with aryl- or alkylsulphate esters in laboratory media and showed significantly reduced survival compared with the parent strain during incubation in Danish agricultural and grassland soils. This effect suggests that sulphate esters are an important sulphur source for microbes in aerobic soils and highlights the importance of the microbial population in the soil sulphur cycle

Sexually transmitted bacteria affect female cloacal assemblages in a wild bird

International audienceSexual transmission is an important mode of disease propagation, yet its mechanisms remain largely unknown in wild populations. Birds comprise an important model for studying sexually transmitted microbes because their cloaca provides a potential for both gastrointestinal pathogens and endosymbionts to become incorporated into ejaculates. We experimentally demonstrate in a wild population of kittiwakes (Rissa tridactyla) that bacteria are transmitted during copulation and affect the composition and diversity of female bacterial communities. We used an anti-insemination device attached to males in combination with a molecular technique (automated ribosomal intergenic spacer analysis) that describes bacterial communities. After inseminations were experimentally blocked, the cloacal communities of mates became increasingly dissimilar. Moreover, female cloacal diversity decreased and the extinction of mate-shared bacteria increased, indicating that female cloacal assemblages revert to their pre-copulatory state and that the cloaca comprises a resilient microbial ecosystem

Involvement of Nitrate Reductase and Pyoverdine in Competitiveness of Pseudomonas fluorescens Strain C7R12 in Soil

Involvement of nitrate reductase and pyoverdine in the competitiveness of the biocontrol strain Pseudomonas fluorescens C7R12 was determined, under gnotobiotic conditions, in two soil compartments (bulk and rhizosphere soil), with the soil being kept at two different values of matric potential (−1 and −10 kPa). Three mutants affected in the synthesis of either the nitrate reductase (Nar(−)), the pyoverdine (Pvd(−)), or both (Nar(−) Pvd(−)) were used. The Nar(−) and Nar(−) Pvd(−) mutants were obtained by site-directed mutagenesis of the wild-type strain and of the Pvd(−) mutant, respectively. The selective advantage given by nitrate reductase and pyoverdine to the wild-type strain was assessed by measuring the dynamic of each mutant-to-total-inoculant (wild-type strain plus mutant) ratio. All three mutants showed a lower competitiveness than the wild-type strain, indicating that both nitrate reductase and pyoverdine are involved in the fitness of P. fluorescens C7R12. The double mutant presented the lowest competitiveness. Overall, the competitive advantages given to C7R12 by nitrate reductase and pyoverdine were similar. However, the selective advantage given by nitrate reductase was more strongly expressed under conditions of lower aeration (−1 kPa). In contrast, the selective advantage given by nitrate reductase and pyoverdine did not differ in bulk and rhizosphere soil, indicating that these bacterial traits are not specifically involved in the rhizosphere competence but rather in the saprophytic ability of C7R12 in soil environments