Effect of Bacillus aryabhattai H26-2 and B. siamensis H30-3 on Growth Promotion and Alleviation of Heat and Drought Stresses in Chinese Cabbage

Plants are exposed to biotic stresses caused by pathogen attack and complex abiotic stresses including heat and drought by dynamic climate changes. To alleviate these stresses, we investigated two bacterial stains, H26-2 and H30-3 in two cultivars (‘Ryeokkwang’ and ‘Buram-3-ho’) of Chinese cabbage in plastic pots in a greenhouse. We evaluated effects of bacterial strains on plant growth-promotion and mitigation of heat and drought stresses; the role of exopolysaccharides as one of bacterial determinants on alleviating stresses; biocontrol activity against soft rot caused by Pectobacterium carotovorum subsp. carotovorum PCC21. Strains H26-2 and H30-3 significantly increased fresh weights compared to a MgSO4 solution; reduced leaf wilting and promoted recovery after re-watering under heat and drought stresses. Chinese cabbages treated with H26-2 and H30-3 increased leaf abscisic acid (ABA) content and reduced stomatal opening after stresses treatments, in addition, these strains stably colonized and maintained their populations in rhizosphere during heat and drought stresses. As well as tested bacterial cells, exopolysaccharides (EPS) of H30-3 could be one of bacterial determinants for alleviation of tested stresses in Chinese cabbages, however, the effects were different to cultivars of Chinese cabbages. In addition to bacterial activity to abiotic stresses, H30-3 could suppress incidence (%) of soft rot in ‘Buram-3-ho’. The tested strains were identified as Bacillus aryabhattai H26-2 and B. siamensis H30-3 based on 16S rRNA gene sequence analysis. Taken together, H26-2 and H30-3 could be candidates for both plant growth promotion and mitigation of heat and drought stresses in Chinese cabbage

Streptomyces brevispora sp nov and Streptomyces laculatispora sp nov., actinomycetes isolated from soil

The taxonomic positions of two actinomycetes isolated from a hay meadow soil sample were determined using a polyphasic approach. The isolates had chemical and morphological properties typical of streptomycetes and formed a distinct 16S rRNA gene subclade together with the type strain Streptomyces drozdowiczii NRRL B-24297(T). DNA DNA relatedness studies showed that the three strains belonged to different genomic species. The organisms were also distinguished using a combination of phenotypic properties. On the basis of these data it is proposed that the isolates be assigned to the genus Streptomyces as Streptomyces brevispora sp. nov. and Streptomyces laculatispora sp. nov., with BK160(T) (=KACC 21093(T) =NCIMB 14702(T)) and BK166(T) (=KACC 20907(T) =NCIMB 14703(T)) as the respective type strains.Conselho Nacional de Desenvolvimento Cientifico e TecnologicoConselho Nacional de Desenvolvimento Cientifico e Tecnologico [201066/2009-2

Enhancement of Tomato Tolerance to Biotic and Abiotic Stresses by Variovorax sp. PMC12

Rhizobacteria play important roles in plant growth and health enhancement and render them resistant to not only biotic stresses but also abiotic stresses, such as low/high temperature, drought, and salinity. This study aimed to select plant growth promoting rhizobacteria (PGPR) with the capability to mitigate biotic and abiotic stress effects on tomato plants. We isolated a novel PGPR strain, Variovorax sp. PMC12 from tomato rhizosphere. An in vitro assay indicated that strain PMC12 produced ammonia, indole-3-acetic acid (IAA), siderophore, and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, which are well-known traits of PGPR. The aboveground fresh weight was significantly higher in tomato plants treated with strain PMC12 than in non-treated tomato plants under various abiotic stress conditions including salinity, low temperature, and drought. Furthermore, strain PMC12 also enhanced the resistance to bacterial wilt disease caused by Ralstonia solanacearum. Taken together, these results indicated that strain PMC12 is a promising biocontrol agent and a biostimulant to reduce the susceptibility of plants to both abiotic and biotic stresses

Phytobacter palmae sp. nov., a novel endophytic, N2 fixing, plant growth promoting Gammaproteobacterium isolated from oil palm (Elaeis guineensis Jacq.)

A novel strain S29T with high nitrogen fixing ability was isolated from surface-sterilized leaf tissues of oil palm (Elaeis guineensis) growing in Science Park II, Singapore. On the basis of 16S rRNA gene analysis and multilocus sequence typing with the rpoB, gyrB, infB and atpD genes, strain S29T was a member of the genus Phytobacter , with Phytobacter ursingii ATCC 27989T and Phytobacter diazotrophicus LS 8T as its closest relatives. Unique biochemical features that differentiated strain S29T from its closest relatives were the ability to utilize melibiose, α-cyclodextrin, glycogen, adonital, D-arabitol, m-inositol and xylitol. The major fatty acids were C14 : 0, C16 : 0, C17 : 0, C16 : 1 ω5c and summed feature 2 containing C16 : 1 ω7c and/or C16 : 1 ω6c. The polar fatty acid profile consisted of phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, an unidentified aminophospholipid and aminolipids. The draft genome of strain S29T comprised 5, 284, 330 bp with a G + C content of 52.6 %. The average nucleotide identity and digital DNA–DNA hybridization values between strain S29T and the phylogenetically related Enterobacterales species were lower than 95 % and 70 %, respectively. Thus, the polyphasic evidences generated through the phenotypic, chemotaxonomic and genomic methods confirmed that strain S29T represents a novel species of the genus Phytobacter , for which we propose the name Phytobacter palmae sp. nov. with the type strain of S29T (=DSM 27342T=KACC 17598T)