Rhodoalgimonas zhirmunskyi gen. nov., sp. nov., a Marine Alphaproteobacterium Isolated from the Pacific Red Alga Ahnfeltia tobuchiensis: Phenotypic Characterization and Pan-Genome Analysis

A novel Gram-staining negative, strictly aerobic, rod-shaped, and non-motile bacterium, designated strain 10Alg 79T, was isolated from the red alga Ahnfeltia tobuchiensis. A phylogenetic analysis based on 16S rRNA gene sequences placed the novel strain within the family Roseobacteraceae, class Alphaproteobacteria, phylum Pseudomonadota, where the nearest neighbor was Shimia sediminis ZQ172T (97.33% of identity). However, a phylogenomic study clearly showed that strain 10Alg 79T forms a distinct evolutionary lineage at the genus level within the family Roseobacteraceae combining with strains Aquicoccus porphyridii L1 8-17T, Marimonas arenosa KCTC 52189T, and Lentibacter algarum DSM 24677T. The ANI, AAI, and dDDH values between them were 75.63-78.15%, 67.41-73.08%, and 18.8-19.8%, respectively. The genome comprises 3,754,741 bp with a DNA GC content of 62.1 mol%. The prevalent fatty acids of strain 10Alg 79T were C18:1 ω7c and C16:0. The polar lipid profile consisted of phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, an unidentified aminolipid, an unidentified phospholipid and an unidentified lipid. A pan-genome analysis showed that the unique part of the 10Alg 79T genome consists of 13 genus-specific clusters and 413 singletons. The annotated singletons were more often related to transport protein systems, transcriptional regulators, and enzymes. A functional annotation of the draft genome sequence revealed that this bacterium could be a source of a new phosphorylase, which may be used for phosphoglycoside synthesis. A combination of the genotypic and phenotypic data showed that the bacterial isolate represents a novel species and a novel genus, for which the name Rhodoalgimonas zhirmunskyi gen. nov., sp. nov. is proposed. The type strain is 10Alg 79T (=KCTC 72611T = KMM 6723T).

Marimonas lutisalis sp. nov., isolated from a tidal mudflat and emended description of the genus Marimonas

A Gram-reaction-negative bacterial strain, designated GH1-19^T, was isolated from a tidal mudflat sample collected in Gangwha Island, Republic of Korea. Cells of the novel micro-organism were strictly aerobic, non-sporulating, motile and rod-shaped. Growth occurred at 10-40 °C (optimum, 30 °C), pH 6-9 (pH 8) and in the presence of 1-9 % NaCl (3 %). Comparative analysis of complete or nearly complete 16S rRNA gene sequences exhibited that strain GH1-19^T formed a distinct cluster between Marimonas arenosa CAU 1311^T (97.42 % sequence similarity) and Aquicoccus porphyridii L1 8-17^T (97.35 %). Similarity levels of 16S rRNA gene sequences between the novel strain and other members of the family Rhodobacteraceae were below 96.6 %. The isoprenoid quinone was Q-10. The major fatty acids were C_18 : 1ω7c, C_16 : 0, summed feature 3 (C_16 : 0 ω7c and/or C_16 : 0 ω6c) and C_12 : 0 3-OH. The polar lipids consisted of diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, an unidentified aminolipid, an unidentified phospholipid and an unidentified lipid. The G+C content of the DNA was 63.2 mol% (draft genome). DNA-DNA relatedness value between the novel strain and the type strain of Marimonas arenosa was 12.7±9.0 %. On the basis of data from phenotypic, chemotaxonomic and DNA-DNA hybridization studies together with phylogenetic analyses, strain GH1-19^T (=KCTC 62376^T=DSM 106292^T) represents a novel species of the genus Marimonas, for which the name Marimonas lutisalis sp. nov. is proposed, with the emended description of the genus Marimonas.

Dynamics of Heterotrophic Bacterial Assemblages within Synechococcus Cultures

Interactions between photoautotrophic and heterotrophic microorganisms are central to the marine microbial ecosystem. Lab cultures of one of the dominant marine photoautotrophs, Synechococcus, have historically been difficult to render axenic, presumably because these bacteria depend upon other organisms to grow under these conditions. These tight associations between Synechococcus and heterotrophic bacteria represent a good relevant system to study interspecies interactions. Ten individual Synechococcus strains, isolated from eutrophic and oligotrophic waters, were chosen for investigation. Four to six dominant associated heterotrophic bacteria were detected in the liquid cultures of each Synechococcus isolate, comprising members of the Cytophaga-Flavobacteria-Bacteroides (CFB) group (mainly from Flavobacteriales and Cytophagales), Alphaproteobacteria (mainly from the Roseobacter clade), Gammaproteobacteria (mainly from the Alteromonadales and Pseudomonadales), and Actinobacteria The presence of the CFB group, Gammaproteobacteria, and Actinobacteria showed clear geographic patterns related to the isolation environments of the Synechococcus bacteria. An investigation of the population dynamics within a growing culture (XM-24) of one of the isolates, including an evaluation of the proportions of cells that were free-living versus aggregated/attached, revealed interesting patterns for different bacterial groups. In Synechococcus sp. strain XM-24 culture, flavobacteria, which was the most abundant group throughout the culture period, tended to be aggregated or attached to the Synechococcus cells, whereas the actinobacteria demonstrated a free-living lifestyle, and roseobacters displayed different patterns depending on the culture growth phase. Factors contributing to these succession patterns for the heterotrophs likely include interactions among the culture community members, their relative abilities to utilize different compounds produced by Synechococcus cells and changes in the compounds released as culture growth proceeds, and their responses to other changes in the environmental conditions throughout the culture period.IMPORTANCE Marine microbes exist within an interactive ecological network, and studying their interactions is an important part of understanding their roles in global biogeochemical cycling and the determinants of microbial diversity. In this study, the dynamic relationships between Synechococcus spp. and their associated heterotrophic bacteria were investigated. Synechococcus-associated heterotrophic bacteria had similar geographic distribution patterns as their "host" and displayed different lifestyles (free-living versus attached/aggregated) according to the Synechococcus culture growth phases. Combined organic carbon composition and bacterial lifestyle data indicated a potential for succession in carbon utilization patterns by the dominant associated heterotrophic bacteria. Comprehending the interactions between photoautotrophs and heterotrophs and the patterns of organic carbon excretion and utilization is critical to understanding their roles in oceanic biogeochemical cycling.

Amylibacter cionae sp. nov., isolated from the sea squirt Ciona savignyi

A Gram-stain-negative, non-motile, aerobic and rod-shaped bacterial strain, designated H-12T, was isolated from a sea squirt (Ciona savignyi) collected from Tsingtao Port, Jiaozhou Bay, China, and its taxonomic position was investigated. Strain H-12T grew optimally at 25-30 °C, at pH 7.0-8.0 and in the presence of 3.0-4.0 % (w/v) NaCl. The 16S rRNA gene sequence of strain H-12T exhibited the highest similarity to that of the type strain of Amylibacter marinus (95.3 %). A neighbour-joining phylogenetic tree based on 16S rRNA gene sequences revealed that strain H-12T clustered with the type strain of A. marinus. The predominant ubiquinone in strain H-12T was identified as Q-10. The major fatty acids of strain H-12T were C18 : 1ω7c and C18 : 1ω7c 11-methyl. The major polar lipids detected in strain H-12T were phosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, one unidentified aminolipid, two unidentified phospholipids and five unidentified lipids. The DNA G+C content of strain H-12T was 52.7 mol%. On the basis of phylogenetic, chemotaxonomic and phenotypic properties, strain H-12T is considered to represent a novel species within the genus Amylibacter, for which the name Amylibacter cionae sp. nov. is proposed. The type strain is H-12T (=KCTC 52581T=CGMCC 1.15880T).