Desulfurization of aromatic sulfonates by rhizosphere bacteria: high diversity of the asfA gene

Abstract

The plant growth-promoting effect of Pseudomonas putida S-313 is associated with its ability to desulfurize arylsulfonates. To understand this further, other plant-associated bacteria able to desulfurize a range of arylsulfonates were isolated from the rhizospheres of winter and spring barley. The isolates belonged to the beta-proteobacteria, including bacteria from the Variovorax paradoxus group and from the Acidovorax genus. They desulfurized toluenesulfonate to p-cresol, and were found to contain orthologues of the P. putida S-313 asfA gene (> 70% sequence identity to AsfA), which is required for aryldesulfonation in this species. Further putative asfA orthologues were identified in several bacteria and cyanobacteria whose genomes have been sequenced, but of these only Cupriavidus (Ralstonia) metallidurans was able to utilize arylsulfonates as sulfur source. Cultivation of V. paradoxus, C. metallidurans or P. putida S-313 with toluenesulfonate as sulfur source led to a 100-fold increase in expression of the asfA homologues, which was largely repressed when sulfate was added. Polymerase chain reaction with degenerate primers was used to generate asfAB clone libraries from spring- and winter-barley rhizosphere DNA. Cluster analysis of 76 sequenced AsfA fragments revealed a broad diversity, with the majority of the sequences clustered together with AsfA from bacteria that are able to utilize toluenesulfonate as sulfur source. The diversity of asfA in barley rhizosphere underlines the importance of the desulfonation process for bacteria that inhabit the plant rhizosphere.

Normal Operating Range of Bacterial Communities in Soil Used for Potato Cropping

“…Quantification of bacterial 16S rRNA genes was performed by quantitative PCR (qPCR) with primers 341F and 518R (7,19). The PCR conditions were as follows: 95°C for 10 min, followed by 40 cycles of 15 s at 95°C, 20 s at 55°C, and 20 s at 72°C.…”

“…The reaction mixture (total volume, 10 l) contained 5 l of DyNamo capillary SYBR green qPCR master mixture (Finnzymes, Helsinki, Finland), 0.3 pmol of forward and reverse primers, and 5 ng of template DNA. The qPCR standards (between 10 6 and 10 10 target molecules per reaction) were prepared using PCR products made from Variovorax paradoxus DSM30034T (19). The 16S rRNA gene target numbers were taken as proxies for bacterial abundances across the samples (expressed as log numbers of 16S rRNA gene copies per g soil).…”

“…In addition to the direct effects exerted by plant root exudates on the soil microbiota, it is important to assess the stability of the latter over the time following removal of the crop plants with respect to abundance, diversity, and community composition, particularly when GM plants have been used (6,(17)(18)(19). Moreover, an assessment of any putative effects of previous crops on the growth of subsequent ones is relevant (20).…”

Unravelling the complete genome sequence of Advenella mimigardefordensis strain DPN7T and novel insights in the catabolism of the xenobiotic polythioester precursor 3,3′-dithiodipropionate

“…Therefore, numerous micro-organisms have developed a variety of pathways to make sulfur available for their central metabolism. The active inter-conversion of organic and inorganic sulfur forms in soil is due to microbial activities, and a plant-growth-promoting effect was demonstrated for desulfonating bacterial strains (Kertesz & Mirleau, 2004;Schmalenberger & Kertesz, 2007;Schmalenberger et al, 2008). The ssu genes are known to be responsible for uptake and degradation of aliphatic sulfonates other than taurine (Eichhorn et al, 2000); accordingly, nine putative ssuABC clusters, which code for ABC-type aliphatic sulfonate transport systems, were identified in the genome of A. mimigardefordensis strain DPN7 T (Table S3).…”

Plant host habitat and root exudates shape soil bacterial community structure

“…Certain bacteria are considered as beneficial, because they produce phytohormones (Azospirillum and Pseudomonas) (Mantelin and Touraine, 2004;Preston, 2004) and antifungal compounds (Stenotrophomonas, Pseudomonas and Microbacterium) (Preston, 2004;Kai et al, 2007;Zachow et al, 2008) or contribute to biogeochemical cycling of sulphur (Acidovorax) (Schmalenberger and Kertesz, 2007) or nitrogen, as diazotrophs and denitrifiers (Azospirillum) (Costacurta and Vanderleyden, 1995). Bacteria considered as human opportunistic pathogens, such as Stenotrophomonas maltophilia, Enterobacter cloacae (Berg et al, 2005) or vine phytopathogenic bacteria, such as Xylophilus ampelinus (Grall and Manceau, 2003), were able to assimilate root exudates and to proliferate in the rhizosphere of different plant species.…”