No abstract

Ralstonia solanacearum species complex (RSSC) strains are bacteria that colonize plant xylem tissue and cause vascular wilt diseases. However, individual strains vary in host range, optimal disease temperatures and physiological traits. To increase our understanding of the evolution, diversity and biology of the RSSC, we performed a meta-analysis of 100 representative RSSC genomes. These 100 RSSC genomes contain 4940 genes on average, and a pangenome analysis found that there are 3262 genes in the core genome (~60 % of the mean RSSC genome) with 13 128 genes in the extensive flexible genome. A core genome phylogenetic tree and a whole-genome similarity matrix aligned with the previously named species ( R. solanacearum , R. pseudosolanacearum , R. syzygii ) and phylotypes (I–IV). These analyses also highlighted a third unrecognized sub-clade of phylotype II. Additionally, we identified differences between phylotypes with respect to gene content and recombination rate, and we delineated population clusters based on the extent of horizontal gene transfer. Multiple analyses indicate that phylotype II is the most diverse phylotype, and it may thus represent the ancestral group of the RSSC. We also used our genome-based framework to test whether the RSSC sequence variant (sequevar) taxonomy is a robust method to define within-species relationships of strains. The sequevar taxonomy is based on alignments of a single conserved gene (egl). Although sequevars in phylotype II describe monophyletic groups, the sequevar system breaks down in the highly recombinogenic phylotype I, which highlights the need for an improved, cost-effective method for genotyping strains in phylotype I. Finally, we enabled quick and precise genome-based identification of newly sequenced RSSC strains by assigning Life Identification Numbers (LINs) to the 100 strains and by circumscribing the RSSC and its sub-groups in the LINbase Web service.

No abstract

Five halophilic bacterial isolates namely SS1, SS2, SS3, SS5 and SS8 were isolated from soil sediments of Lunsu, a salty water body. All the bacterial isolates showed growth in LB medium containing up to 8.7% NaCl, pH 7–8 and at temperature range of 30–37°C. The bacterial isolates SS1 and SS3 require at least 3.8% NaCl for their growth, indicating their strict halophilic nature. Interestingly, bacterial isolates SS2, SS5 and SS8 but not SS1 and SS3 exhibited growth in medium supplemented with KCl. Accordingly, Na+ and K+ ions were detected at 1.39 and 0.0035%, respectively in Lunsu water. All the bacterial isolates were analyzed by random amplification of polymorphic DNA (RAPD) using four different random primers and produced PCR fragments ranging from 0.1 to 5 kb in size. Phylogenetic tree based on RAPD finger prints showed that SS1 and SS3 formed one group, while SS2 and SS5 formed the second group, whereas SS8 was out group. Sequence analysis of 16S rDNA identified SS1 and SS3 as Halobacillus trueperi, SS2 as Shewanella algae, SS5 as Halomonas venusta, and SS8 as Marinomonas sp. were deposited in GenBank with accession numbers of KM260166, KF751761, KF751760, KF751762 and KF751763, respectively. This is the first report on the presence of diverse halophilic bacteria in the foot hills of Himalayas.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-015-1028-1) contains supplementary material, which is available to authorized users.

The halophilic bacterial isolates SS1, SS2, SS3, SS5, and SS8 were characterized for production of industrially important enzymes like amylase, protease, lipase, and glutaminase. Halophilic bacterial isolates SS1 and SS3 exhibited salt dependent extracellular amylase and protease activities. Both the halophilic isolates SS1 and SS3 exhibited maximum amylase and protease activities in the presence of 1.5 and 1.0 M NaCl, respectively, with the optimum pH 8 and temperature 40°C. SS2 showed maximum extracellular protease and lipase activities in the presence of 0.75 M NaCl, at optimum pH of 7, and temperature 37°C. The glutaminase activity of SS3 increased with increase in concentration of NaCl up to 2.5 M. The optimum pH and temperature for L-glutaminase activity of SS3 was 8 and 40°C, respectively. The combined hydrolytic activities of these halophilic bacterial isolates can be used for bioconversion of organic materials to useful products.