Litorilituus lipolyticus sp. nov., isolated from intertidal sand of the Yellow Sea in China, and emended description of Colwellia asteriadis

Understanding the mechanisms of halotolerance in members of Pontixanthobacter and Allopontixanthobacter by comparative genome analysis

Halotolerant microorganisms have developed versatile mechanisms for coping with saline stress. With the increasing number of isolated halotolerant strains and their genomes being sequenced, comparative genome analysis would help understand the mechanisms of salt tolerance. Six type strains of Pontixanthobacter and Allopontixanthobacter, two phylogenetically close genera, were isolated from diverse salty environments and showed different NaCl tolerances, from 3 to 10% (w/v). Based on the co-occurrence greater than 0.8 between halotolerance and open reading frame (ORF) among the six strains, possible explanations for halotolerance were discussed regarding osmolyte, membrane permeability, transportation, intracellular signaling, polysaccharide biosynthesis, and SOS response, which provided hypotheses for further investigations. The strategy of analyzing genome-wide co-occurrence between genetic diversity and physiological characteristics sheds light on how microorganisms adapt to the environment.

Pontixanthobacter rizhaonensis sp. nov., a marine bacterium isolated from surface seawater of the Yellow Sea, and proposal of Pseudopontixanthobacter gen. nov., Pseudopontixanthobacter confluentis comb. nov. and Pseudopontixanthobacter sediminis comb. nov

A bacterial strain designated RZ02^T was isolated from surface seawater collected from the Yellow Sea in PR China and characterized by polyphasic taxonomy. Cells of strain RZ02^T were Gram-stain-negative, aerobic, non-motile, catalase- and oxidase-positive rods forming ochre-pigmented colonies. Growth occurred at 7-36 °C (optimum, 30 °C), at pH 6.0-9.0 (optimum, pH 7.0) and with 1-5 % (optimum, 2 %) NaCl. The major cellular fatty acids (>10 %) of strain RZ02^T were summed feature 8 (C_18 : 1  ω6c and/or C_18 : 1  ω7c), summed feature 3 (C_16 : 1  ω7c and/or C_16 : 1  ω6c) and C_16 : 0. The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, diphosphatidylglycerol and sphingoglycolipid. The genome size of strain RZ02^T was 2.79 Mbp with a G+C content of 55.5 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain RZ02^T was mostly related to Pontixanthobacter luteolus SW-109^T and Pontixanthobacter aestiaquae HDW-31^T (97.3 and 97.1% sequence similarity, respectively), and formed a phyletic lineage with members of the genus Pontixanthobacter. The phylogenetic analysis based on the up-to-date bacterial core gene sequences confirmed that strain RZ02^T clustered within the genus Pontixanthobacter. The average nucleotide identity and in silico DNA-DNA hybridization values between strain RZ02^T and P. luteolus SW-109^T and P. aestiaquae HDW-31^T were 72.8 and 72.9 % and 18.7 and 18.5%, respectively. Based on these evidences, strain RZ02^T is proposed to represent a novel species of the genus Pontixanthobacter under the name Pontixanthobacter rizhaonensis sp. nov. The type strain is RZ02^T (=KCTC 62828^T=MCCC 1K04521^T). In addition, based on the results of whole genome analyses, proposals of Pseudopontixanthobacter gen. nov., Pseudopontixanthobacter confluentis comb. nov. and Pseudopontixanthobacter sediminis comb. nov. are also included.