Enterobacter cloacae GS1 was isolated by in-planta enrichment of a rice rhizoplane bacterial community. It displayed strong seed adherence ability (2.5 × 10(5) cfu/seed) and colonized rice roots reaching up to 1.65 × 10(9) cfu/g of fresh root weight in a gnotobiotic root colonization system. E. cloacae GS1 was motile, able to solubilize tricalcium phosphate, and produced indole acetic acid like substances (15 μg/ml). As an introduced bioinoculant in non-sterile soil, E. cloacae GS1 colonized rice roots and significantly improved the fresh weight, root length, shoot length, and nitrogen content in inoculated rice seedlings as compared to uninoculated controls. This isolate was tagged with green fluorescent protein and various stages of root colonization in gnotobiotic hydroponic environment and non-sterile soil environment were followed by fluorescence microscopy. Owing to its effective root colonizing ability and growth promoting potential, Enterobacter cloacae GS1 is a promising symbiotic bioinoculant for rice.

Fluorescent pseudomonads catabolize glucose simultaneously by two different pathways, namely, the oxidative pathway in periplasm and the phosphorylative pathway in cytoplasm. This study provides evidence for the role of glucose metabolism in the regulation of pyoverdine synthesis in Pseudomonas putida S11. We have characterized the influence of direct oxidation of glucose in periplasm on pyoverdine synthesis in P. putida S11. We identified a Tn5 transposon mutant of P. putida S11 showing increased pyoverdine production in minimal glucose medium (MGM). This mutant designated as IST1 had Tn5 insertion in glucose dehydrogenase (gcd) gene. To verify the role of periplasmic oxidation of glucose on pyoverdine synthesis, we constructed mutants S11 Gcd(-) and S11 PqqF(-) by antibiotic cassette mutagenesis. These mutants of P. putida S11 with loss of glucose dehydrogenase gene (gcd) or cofactor pyrroloquinoline quinone biosynthesis gene (pqqF) showed increased pyoverdine synthesis and impaired acid production in MGM. In minimal gluconate medium, the pyoverdine production of wild-type strain S11 and mutants S11 Gcd(-) and S11 PqqF(-) was higher than in MGM indicating that gluconate did not affect pyoverdine synthesis. In MGM containing PIPES-NaOH (pH 7.5) buffer which prevent pH changes due to gluconic acid production, strain S11 produced higher amount of pyoverdine similar to mutants S11 Gcd(-) and S11 PqqF(-). Therefore, it is proposed that periplasmic oxidation of glucose to gluconic acid decreases the pH of MGM and thereby influences pyoverdine synthesis of strain S11. The increased pyoverdine synthesis enhanced biotic and abiotic surface colonization of the strain S11.

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Here we report the genome sequence of a plant growth-promoting rhizobacterium, Pseudomonas putida S11. The length of the draft genome sequence is approximately 5,970,799 bp, with a G؉C content of 62.4%. The genome contains 6,076 protein-coding sequences. P lant growth-promoting rhizobacteria (PGPR) colonize the rhizosphere and promote plant growth through either direct or indirect mechanisms. Root colonization is the crucial step that determines the success of the plant growth promotion. Pseudomonas putida S11 was isolated from the sugarcane rhizosphere. It efficiently colonizes corn roots and promotes plant growth. This strain was submitted to the Microbial Type Culture Collection and Gene Bank (MTCC), Chandigarh, India, with the accession number MTCC 5670. Earlier, we identified that a mutation of the two-component signal transduction system (pstSR) in P. putida S11 increased pyoverdine production and iron uptake, which, in turn, results in improved abiotic and biotic surface colonization (4). Whole-genome shotgun sequencing of P. putida S11 was done to further understand genes essential for root colonization and survival in the rhizosphere.Total genomic DNA of P. putida S11 was isolated using the Qiagen DNeasy kit by following the manufacturer's instructions. The sequencing was performed by Roche 454 pyrosequencing at the Research and Testing Laboratory, Lubbock, TX. The data generated contained 230,568 reads with an average read length of 588 bp. Altogether, 135,627,871 sequenced bases were obtained with an ϳ22-fold coverage of the ϳ5.9-Mb genome. The de novo assembly using MIRA (Mimicking Intelligent Read Assembly) version 3.4.0 (2) yielded 346 contigs (N 50 length ϭ 32,259 bp). The Staden package, version 2.0 (5), was used to visualize contigs and to join the overlapping contigs, which finally yielded 196 contigs (longest contig ϭ 255,672 bp; shortest contig ϭ 349 bp). The consensus length of the draft genome sequence is 5,970,799 bp, with a GϩC content of 62.4%. The draft genome was annotated using the Rapid Annotations using Subsystems Technology (RAST; version 4.0) (1) server with the RAST gene caller. A total of 6,076 protein-coding genes and 85 RNA coding regions were predicted.The bioavailability of iron is low in the rhizosphere. PGPR require efficient iron acquisition mechanisms to compete with other microorganisms and plants for uptake of the essential micronutrient (3). The genome of P. putida S11 contains 31 genes with predicted function in siderophore pyoverdine biosynthesis, transport, and regulation. In addition, 25 putative TonB-dependent siderophore receptor genes involved in iron transport are identified. Predicted sigma factor/anti-sigma factor gene pairs are found flanking six of these putative siderophore receptor genes. Further analysis of the functional role of these predicted genes in iron acquisition and metabolism and the influence of iron uptake in root colonization of strain S11 are presently being investigated. The draft genome sequence of P. putida S11 provides a framework for ...