Spirosoma endbachense sp. nov., isolated from a natural salt meadow.

A Gram-stain-negative bacterium, designated I-24T, was isolated from soil of a natural salt meadow. Strain I-24T was aerobic, non-motile, rod-shaped, catalase-positive, oxidase-positive and grew optimally at pH 7 and 25 °C. Comparative 16S rRNA gene analysis indicated that strain I-24T has closest similarities to Spirosoma agri KCTC 52727T (95.9 %) and Spirosoma terrae KCTC 52035T (95.5 %). Strain I-24T contained summed feature 3 (C16 : 1 ω7c/C16 : 1 ω6c) and C16 : 1 ω5c as the major fatty acids, the predominant respiratory quinone was menaquinone MK-7, and the major polar lipids were phosphatidylethanolamine as well as an unidentified phosphoaminolipid. The draft genome of strain I-24T consists of 10 326 072 base pairs with 9153 predicted coding sequences and a G+C content of 47.7 mol%. Clear distinctions between strain I-24T and S. agri KCTC 52727T or S. terrae KCTC 52035T were shown in the pairwise average nucleotide identity results with values of 76.71 and 74.01 %, respectively. Moreover, the digital DNA-DNA relatedness values to these strains were 20.8 and 19.0 %. Based on its phenotypic, genotypic and chemotaxonomic characteristics, strain I-24T represents a novel species of the genus Spirosoma, for which the name Spirosoma endbachense sp. nov. is proposed. The type strain is I-24T (DSM 111055T=KCTC 72613T).

Ancylobacter pratisalsi sp. nov. with plant growth promotion abilities from the rhizosphere of Plantago winteri Wirtg.

A Gram-negative bacterium, designated E130T, was isolated from rhizospheric soil of Plantago winteri Wirtg. from a natural salt meadow as part of an investigation on rhizospheric bacteria from salt-resistant plant species and evaluation of their plant growth-promoting abilities. Cells were rods, non-motile, aerobic, and oxidase and catalase positive, grew in a temperature range of between 4 and 37 °C, and in the presence of 0.5-5 % NaCl (w/v). Based on 16S rRNA gene sequence analysis, strain E130T is affiliated within the genus Ancylobacter, sharing the highest similarity with Ancylobacter rudongensis DSM 17131T (97.6 %), Ancylobacter defluvii CCUG 63806T (97.5 %) and Ancylobacter dichloromethanicus DSM 21507T (97.4 %). The DNA G+C content of strain E130T was 65.1 mol%. Its respiratory quinones were Q-9 and Q-10 and its major polar lipids comprised phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine and unidentified phospholipid. Major fatty acids of the strains E130T were C12 : 0, C16 : 0, C18 : 1ω7c and C19 : 0cycloω8c. The DNA-DNA relatedness of E130T to A. rudongensis DSM 17131T, A. defluvii CCUG 63806T and A. dichloromethanicus DSM 21507T was 29.2, 21.2 and 32.2 % respectively. On the basis of our polyphasic taxonomic study the new isolate represents a novel species, for which the name Ancylobacter pratisalsi sp. nov. is proposed. The type strain is E130T (LMG 29367T=DSM 102029T).

Paradox of plant growth promotion potential of rhizobacteria and their actual promotion effect on growth of barley (Hordeum vulgare L.) under salt stress.

From the rhizosphere of two salt tolerant plant species, Hordeum secalinum and Plantago winteri growing in a naturally salt meadow, 100 strains were isolation on enrichment media for various plant growth-promoting (PGP) functions (ACC deaminase activity, auxin synthesis, calcium phosphate mobilization and nitrogen fixation). Based on the taxonomic affiliation of the isolated bacteria and their enrichment medium 22 isolates were selected to test their growth promotion effect on the crop barley (Hordeum vulgare) under salt stress in pot experiment. In parallel the isolates were characterized in pure culture for their plant growth-promoting activities. Surprisingly the best promotors did not display a promising set of PGP activities. Isolates with multiple PGP-activities in pure culture like Microbacterium natoriense strain E38 and Pseudomonas brassicacearum strain E8 did not promote plant growth. The most effective isolate was strain E108 identified as Curtobacterium flaccumfaciens, which increased barley growth up to 300%. In pure culture strain E108 showed only two out of six plant growth promoting activities and would have been neglected. Our results highlight that screening based on pure culture assays may not be suitable for recognition of best plant growth promotion candidates and could preclude the detection of both new PGPR and new plant promotion mechanisms.