Zenghu Zhang

Quorum sensing in marine snow and its possible influence on production of extracellular hydrolytic enzymes in marine snow bacterium Pantoea ananatis B9

Marine snow is a continuous shower of organic and inorganic detritus, and plays a crucial role in transporting materials from the sea surface to the deep ocean. The aims of the current study were to identify N-acyl homoserine lactone (AHL)-based quorum sensing (QS) signaling molecules directly from marine snow particles and to investigate the possible regulatory link between QS signals and extracellular hydrolytic enzymes produced by marine snow bacteria. The marine snow samples were collected from the surface water of China marginal seas. Two AHLs, i.e. 3OC6-HSL and C8-HSL, were identified directly from marine snow particles, while six different AHL signals, i.e. C4-HSL, 3OC6-HSL, C6-HSL, C10-HSL, C12-HSL and C14-HSL were produced by Pantoea ananatis B9 inhabiting natural marine snow particles. Of the extracellular hydrolytic enzymes produced by P. ananatis B9, alkaline phosphatase activity was highly enhanced in growth medium supplemented with exogenous AHL (C10-HSL), while quorum quenching enzyme (AiiA) drastically reduced the enzyme activity. To our knowledge, this is the first report revealing six different AHL signals produced by P. ananatis B9 and AHL-based QS system enhanced the extracellular hydrolytic enzyme in P. ananatis B9. Furthermore, this study first time revealing 3OC6-HSL production by Paracoccus carotinifaciens affiliated with Alphaproteobacteria.

Edwardsiella tarda invasion of fish cell lines and the activation of divergent cell death pathways.

Edwardsiella tarda is an important gram-negative intracellular pathogen of fish. However, the invasive features of E. tarda to fish cells and the pathogenesis of host cell death have not been thoroughly investigated. In this study, two fish cell models were used to investigate the interactions between E. tarda and its cellular hosts. E. tarda invaded and replicated in both cell lines. Epithelioma papulosum cyprini (EPC) cells were more sensitive to E. tarda infection than the flounder gill cell line FG-9307, with higher levels of intracellular bacteria in the former. The invasion and intracellular replication of E. tarda in FG-9307 cells were studied at the ultrastructural level, and infected cells with large amounts of replicated bacteria and destroyed organelles were observed. Apoptosis was observed in EPC cells upon infection, characterized by the occurrence of apoptotic bodies, DNA ladder, increased Annexin V binding and the activation of caspase-3, whereas E. tarda infected FG-9307 cells were negative for all of those features. E. tarda infection in FG-9307 cells failed to protect the staurosporine-induced apoptosis. Moreover, both intrinsic and extrinsic pathways were activated in EPC cells upon E. tarda infection. The present study revealed that E. tarda interacts with fish cells in different manners, and divergent pathways were activated in these cellular hosts to mediate cell death. These results provided new information on the interactions between E. tarda and fish cells.

Dokdonia pacifica sp. nov., isolated from seawater

A Gram-stain-negative, aerobic, non-flagellated, non-gliding, oxidase- and catalase-positive, rod-shaped, yellow-pigmented bacterium, designated strain SW230(T), was isolated from a surface seawater sample collected from the South Pacific Gyre. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain SW230(T) shared highest similarity with members of the genus Dokdonia (95.0-94.5%), exhibiting 95.0% sequence similarity to Dokdonia genika NBRC 100811(T). Optimal growth occurred in the presence of 2-3% (w/v) NaCl, at pH 8.0 and at 28 °C. The DNA G+C content of strain SW230(T) was 36 mol%. The major fatty acids (>10% of the total) were iso-C15:1 G, iso-C15:0, iso-C17:0 3-OH, and C16:1 ω7c and/or C16:1ω6c. The major respiratory quinone was menaquinone-6. The major polar lipids were phosphatidylethanolamine, two unidentified aminolipids and two unidentified lipids. On the basis of data from the present polyphasic study, strain SW230(T) is considered to represent a novel species of the genus Dokdonia, for which the name Dokdonia pacifica sp. nov. is proposed. The type strain is SW230(T) ( = CGMCC 1.12184(T) = JCM 18216(T)).

Loktanella sediminum sp. nov., isolated from marine surface sediment.

A Gram-staining-negative, strictly aerobic and short rod-shaped bacterium, designated strain S3B03(T), was isolated from the sediment of the northern Okinawa Trough. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain S3B03(T) belonged to the genus Loktanella (family Rhodobacteraceae) and showed the highest sequence similarity with Loktanella litorea KCTC 23883(T) (96.16 %) and 92.99-95.90 % 16S rRNA gene sequence similarity to other members of the genus Loktanella. Optimal growth occurred in the presence of 2-5 % (w/v) NaCl at pH 7.0-8.0 and 28-32 °C. Ubiquinone-10 (Q-10) was the predominant respiratory quinone. The major fatty acids (>10 % of the total fatty acids) were C18 : 1ω7c and/or C18 : 1ω6c. The major polar lipids were phosphatidylglycerol, diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine and two unidentified polar lipids. The DNA G+C content of strain S3B03(T) was 57.6 mol%. On the basis of polyphasic analysis, strain S3B03(T) is considered to represent a novel species of the genus Loktanella, for which the name Loktanella sediminum sp. nov. is proposed. The type strain is S3B03(T) ( = JCM 30120(T) = DSM 28715(T) = MCCC 1K00257(T)).

Polaribacter pacificus sp. nov., isolated from a deep-sea polymetallic nodule from the Eastern Pacific Ocean

A Gram-staining-negative, yellow-colony-forming, rod-shaped, non-flagellated and facultatively aerobic strain, designed HRA130-1T, was isolated from a deep-sea polymetallic nodule from the Pacific Clarion-Clipperton Fracture Zone (CCFZ). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain HRA130-1T belonged to the genus Polaribacter (96.3-93.2 % 16S rRNA gene sequence similarity), and exhibited 94 % 16S rRNA gene sequence similarity to Polaribacter filamentus KCTC 23135T (type species) and the highest sequence similarity to Polaribacter huanghezhanensis KCTC 32516T (96.3 %). Optimal growth occurred in the presence of 4 % (w/v) NaCl, at pH 7.0 and 16 °C. The DNA G+C content of strain HRA130-1T was 35.9 mol%. The major fatty acid was iso-C15 : 0. The predominant respiratory quinone was menaquinone-6 (MK-6). The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol, one unidentified phospholipid and an unidentified aminolipid. On the basis of data from the present taxonomic study using a polyphasic approach, strain HRA130-1T represents a novel species of the genus Polaribacter, for which the name Polaribacter pacificus sp. nov. is proposed. The type strain is HRA130-1T (=KCTC 52370T=MCCC 1K03199T=JCM 31460T=CGMCC 1.15763T).

Aureibacillus halotolerans gen. nov., sp. nov., isolated from sediment of the northern Okinawa Trough.

A Gram-staining-positive, strictly aerobic, spore-forming and rod-shaped motile bacterium with peritrichous flagellae, designated strain S1203T, was isolated from the sediment of the northern Okinawa Trough. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain S1203T formed a lineage within the family Bacillaceae that was distinct from the most closely related genera Bacillus, Bhargavaea, Planomicrobium and Virgibacillus with gene sequence similarities ranging from 86.2 to 93.76 %. Optimal growth occurred in the presence of 4-8 % (w/v) NaCl, at pH 7.0-8.0 and 25-32 °C. The cell-wall peptidoglycan was based on meso-diaminopimelic acid and unsaturated menaquinone with seven isoprene units (MK-7) as the predominant respiratory quinone. The major fatty acids (>10 % of total fatty acids) were anteiso-C15 : 0, iso-C15 : 0 and C16 : 0.The major polar lipids were phosphatidylglycerol, diphosphatidylglycerol, an unidentified glycolipid and an unidentified phospholipid. The DNA G+C content of strain S1203T was 47.7 mol%. On the basis of polyphasic analysis, strainS1203T was considered to represent a novel species in a new genus of the family Bacillaceae, for which the name Aureibacillus halotolerans gen. nov., sp. nov. is proposed; the type strain of Aureibacillus halotolerans is S1203T ( = DSM 28697T = JCM 30067T = MCCC 1K00259T).

Enterovibrio pacificus sp. nov., isolated from seawater, and emended descriptions of Enterovibrio coralii and the genus Enterovibrio

A Gram-stain-negative, elliptical and facultatively anaerobic strain, designated SW014T, motile by means of a single polar flagellum and positive for poly-β-hydroxybutyrate accumulation, was isolated from surface seawater of the South Pacific Gyre, during the Integrated Ocean Drilling Program Expedition 329. The strain was able to grow at 10-37 °C (optimum 28 °C). Growth was observed at NaCl concentrations (w/v) of 1-7 % (optimum 3-4 %). The pH range for growth was 7.0-9.0 (optimum pH 8.0). Phylogenetic analysis based on 16S rRNA gene sequences and multilocus sequence analysis indicated that strain SW014T belongs to the genus Enterovibrio within the family Vibrionaceae and is related most closely to Enterovibrio coralii LMG 22228T with 96.3, 83.7, 95.0, 77.1, 84.1 and 85.8 % sequence similarity based on 16S rRNA, recA, rpoA, rpoD, pyrH and ftsZ genes, respectively. The predominant cellular fatty acids were C16 : 1ω7c and/or C16 : 1ω6c, C16 : 0, and C18 : 1ω7c and/or C18 : 1ω6c. The respiratory quinone was ubiquinone-8 (Q-8). The polar lipids of strain SW014T comprised phosphatidylethanolamine, glycolipid, two unidentified aminolipids, two unidentified phospholipids and two unidentified polar lipids. The DNA G+C content was 44.8 mol%. Combining phylogenetic analysis, phenotypic characteristics and chemotaxonomic studies, strain SW014T represents a novel species of the genus Enterovibrio, for which the name Enterovibrio pacificus sp. nov. is proposed. The type strain is SW014T ( = KCTC 42425T = MCCC 1K00500T). Emended descriptions of Enterovibrio coralii and of the genus Enterovibrio are also provided.