The Indian Ocean is characterized by its complex physical systems and strong seasonal monsoons. To better understand effects of seasonal monsoon-driven circulation on the bacterioplanktonic community structure in surface waters and the bacterial distribution response to vertical stratification, patterns of seasonal, and vertical distribution of bacterial communities in the Eastern Tropical Indian Ocean were investigated using 16S rRNA gene profiling. Water samples were collected during the Southwest monsoon (from June to August), the fall inter-monsoon (from October and November) and the Northeast monsoon (from December to January), respectively, onboard during three cruises from July 2016 to January 2018. Surface bacterioplankton communities in these three seasons and in the upper water (3–300 m with six depths) during the Northeast monsoon contained a diverse group of taxa, mainly Proteobacteria, Cyanobacteria, Actinobacteria, Bacteroidetes, and Chloroflexi. Redundancy discriminant analysis (RDA) uncovered that temperature, salinity, and dissolved oxygen (DO) were crucial environmental parameters that affected the structure of bacterial community in overall surface samples. However, significant differences in the composition of the bacterial community are likely due to changes in concentrations of salinity during the fall inter-monsoon, while phosphate for both the Southwest monsoon and the Northeast monsoon. Pearson's analysis revealed that the seasonal variation rather than the vertical variation of environmental factors had a more significant impact on the composition of bacterial community. In addition, a clear seasonal pattern of bacterial co-occurrence showed that inter-taxa associations during the fall inter-monsoon were closer than during the Northeast monsoon and the Southwest monsoon. Overall, our results implied clear differences in the composition of bacterial community, with more pronounced seasonal variation compared to the vertical variation in response to environmental changes.

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A Gram-stain-negative, motile, rod-shaped, non-endospore-forming, aerobic and halophilic bacterium, designated strain YCWA18T, was isolated from the sediment of Jimo-Daqiao saltern in China. This strain was able to grow at NaCl concentrations in the range 0.5–20 % (w/v) with optimum growth at 6 % (w/v) NaCl. Growth occurred at temperatures of 4–40 °C (optimum 28 °C) and pH 4.0–9.0 (optimum 7.0). Phylogenetic analysis based on 16S rRNA gene sequences showed that strain YCWA18T belonged to the genus Kushneria and shared the highest sequence similarity of 98.7 % with Kushneria sinocarnis DSM 23229T. Moreover, the phylogenetic analysis based on the 23S rRNA gene sequence also confirmed the phylogenetic position of this novel strain. The predominant fatty acids were C16 : 0, C17 : 0 cyclo and C12 : 0 3-OH. The major isoprenoid quinone was Q-9 (94.2 %) and the polar lipids were diphosphatidylglycerol (DPG), phosphatidylglycerol (PG), phosphatidylethanolamine (PE), an unidentified aminolipid (AL), an unidentified phospholipids (PL) and two unidentified lipids (L). The complete genome of strain YCWA18T consisted of a single, circular chromosome of 3 624 619 bp, with an average G+C content of 59.1 mol%. A genome-based phylogenetic tree constructed using an up-to-date bacterial core gene set (UBCG) showed that strain YCWA18T formed a clade with K. sinocarnis DSM 23229T. However, the level of the ANI and dDDH values between strain YCWA18T and K. sinocarnis DSM 23229T were 82.3 and 24.6 %, respectively, which were low enough to distinguish strain YCWA18T from K. sinocarnis DSM 23229T. Overall, based on the phenotypic, chemotaxonomic, phylogenetic and genomic analyses, strain YCWA18T represents a novel species of genus Kushneria . The name Kushneria phosphatilytica sp. nov. is proposed, with the type strain YCWA18T (=CGMCC 1.9149T=NCCB 100306T).