Vibrio rhizosphaerae sp. nov., a red-pigmented bacterium that antagonizes phytopathogenic bacteria.

Two novel red-pigmented Vibrio strains, MSSRF3(T) and MSSRF10, with antibacterial activity against phytopathogens were isolated from the rhizosphere region of mangrove-associated wild rice (Porteresia coarctata Tateoka), in Pichavaram, India. The cells were Gram-negative, facultatively anaerobic and rod-shaped and were motile by means of single polar flagella. The two strains were catalase-positive and oxidase-negative, and were able to grow in 0.1-10 % NaCl (with optimum growth in 2 % NaCl) and at temperatures of 20-42 degrees C (optimum growth at 25-30 degrees C). Both strains produced acid and gas from D-glucose under anaerobic conditions and utilized a wide range of compounds as sole carbon and energy sources. The DNA G+C contents determined were 51.3 mol% for strain MSSRF3(T) and 51.0 mol% for strain MSSRF10. Phylogenetic analysis based on 16S rRNA, rpoA, recA and pyrH gene sequences showed that strains MSSRF3(T) and MSSRF10 belong to the genus Vibrio and are very closely related to Vibrio ruber JCM 11486(T), with which they share 98.3-98.5 % (16S rRNA), 98.3-99.7 % (rpoA), 90.2-99.8 % (recA) and 91.3-99.4 % (pyrH) gene sequence similarities, respectively. Levels of DNA-DNA relatedness were 44 % between strains MSSRF3(T) and MSSRF10, 80 % between strain MSSRF10 and V. ruber JCM 11486(T) and 45 % between strain MSSRF3(T) and V. ruber JCM 11486(T). Strain MSSRF3(T) was phenotypically similar to V. ruber JCM 11486(T). However, the inability to reduce nitrate to nitrite, the ability to grow in 0.1 % NaCl and the presence of caseinase were characteristics that allowed differentiation between V. ruber JCM 11486(T) and strain MSSRF3(T). In addition, strain MSSRF3(T) could be differentiated from strain MSSRF10 and its closest relative V. ruber JCM 11486(T) with respect to its genomic fingerprinting analysis (random amplified polymorphic DNA, GTG5, BOX, PCR-restriction fragment length polymorphism and ribotyping). Therefore, based on phenotypic, genotypic, phylogenetic and DNA-DNA hybridization analyses, strain MSSRF3(T) (=LMG 23790(T)=DSM 18581(T)) should be classified as representing the type strain of a novel species of the genus Vibrio, for which the name Vibrio rhizosphaerae sp. nov. is proposed.