Ascidiaceibacter salegens gen. nov., sp. nov., isolated from an ascidian

Phylogenetic analysis and screening of antimicrobial and cytotoxic activities of culturable bacteria associated with the ascidian Botryllus schlosseri

AIMS

Isolating culturable bacteria associated with ascidian (Botryllus schlosseri) and investigating their bioactivities to discover new marine microbial resources with potential to produce novel bioactive natural products.

METHODS AND RESULTS

A total of 357 bacteria were isolated from the ascidian B. schlosseri from the coast of Weihai in the north Yellow Sea, China. Of these, 203 isolates were identified by 16S rRNA gene sequencing and they belonged to 52 genera from 30 families in five phyla. The antimicrobial activities and cytotoxic activities of all isolates were determined. Of the 357 isolates, 135 isolates demonstrated antimicrobial activities, and the crude extracts of five isolates showed strong cytotoxicity against human hepatocellular carcinoma Bel 7402 or human cervical carcinoma HeLa cells.

CONCLUSIONS

Our study revealed the diversity of bacteria associated with the ascidian B. schlosseri and reported a broad spectrum of antimicrobial and cytotoxic activities displayed by these isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our results suggest that the culturable bacteria associated with the ascidian B. schlosseri may be a potential source for novel bioactive compounds.

Phylogenetic Analysis and Screening of Antimicrobial and Antiproliferative Activities of Culturable Bacteria Associated with the Ascidian Styela clava from the Yellow Sea, China

Over 1,000 compounds, including ecteinascidin-743 and didemnin B, have been isolated from ascidians, with most having bioactive properties such as antimicrobial, antitumor, and enzyme-inhibiting activities. In recent years, direct and indirect evidence has shown that some bioactive compounds isolated from ascidians are not produced by ascidians themselves but by their symbiotic microorganisms. Isolated culturable bacteria associated with ascidians and investigating their potential bioactivity are an important approach for discovering novel compounds. In this study, a total of 269 bacteria were isolated from the ascidian Styela clava collected from the coast of Weihai in the north of the Yellow Sea, China. Phylogenetic relationships among 183 isolates were determined using their 16S rRNA gene sequences. Isolates were tested for antimicrobial activity against seven indicator strains, and an antiproliferative activity assay was performed to test for inhibition of human hepatocellular carcinoma Bel 7402 and human cervical carcinoma HeLa cell proliferation. Our results showed that the isolates belonged to 26 genera from 18 families in four phyla (Firmicutes, Actinobacteria, Proteobacteria, and Bacteroidetes). Bacillus and Streptomyces were the most dominant genera; 146 strains had potent antimicrobial activities and inhibited at least one of the indicator strains. Crude extracts from 29 strains showed antiproliferative activity against Bel 7402 cells with IC₅₀ values below 500 μg·mL^-1, and 53 strains showed antiproliferative activity against HeLa cells, with IC₅₀ values less than 500 μg·mL^-1. Our results suggest that culturable bacteria associated with the ascidian Styela clava may be a promising source of novel bioactive compounds.

Flavobacterium cerinum sp. nov., isolated from Arctic tundra soil

In the present paper, we describe a new species of the genus Flavobacterium, designated as strain 1E403^T, which was isolated from a soil sample collected from the Arctic. Strain 1E403^T was Gram-stain-negative, yellow-pigmented, rod-shaped, gliding and aerobic. Growth occurred at 4-37 °C (optimum, 28 °C), pH 6.0-9.0 (pH 7.0) and with 0-2 % (w/v) NaCl (0 %) on modified marine agar 2216. Phylogenetic analysis based on 16S rRNA gene sequencing revealed that strain 1E403^T was affiliated with the genus Flavobacterium and was more closely related to Flavobacterium subsaxonicum DSM 21790^T (96.6 %) than to other species. In silico genomic comparisons, including average nucleotide identity and the digital DNA-DNA hybridization values, showed 73.9 % and 18.8 % identity to the closest relative Flavobacterium subsaxonicum DSM 21790^T, respectively. The average amino acid identity value between strain 1E403^T and Flavobacterium aquatile DSM 1132^T was 63.8 %. The DNA G+C content of the strain was 36.8 %, while the sole respiratory quinone was menaquinone-6. Iso-C_15 : 0 and summed feature 3 (C_16 : 1ω7c and/or C_16 : 1ω6c) were the major fatty acids (>10 %) of strain 1E403^T. The polar lipid profile of strain 1E403^T contained phosphatidylethanolamine, four unidentified aminolipids and two unidentified phospholipids. Based on the phenotypic characteristics, chemotaxonomic characteristics and phylogenetic inference, strain 1E403^T represents a novel species of the genus Flavobacterium, and we propose the name Flavobacterium cerinum sp. nov. The type strain of Flavobacterium cerinum sp. nov. is 1E403^T (=KCTC 62960^T=MCCC 1H00356^T).

Marinilabilia rubra sp. nov., isolated from a marine solar saltern

A novel cherry-red-pigmented, Gram-stain-negative, gliding, facultatively anaerobic and rod-shaped bacterium, designated strain WTE16^T, was isolated from a sediment sample taken from a marine solar saltern of Wendeng, China (36° 59' 56.49'' N 122° 1' 38.84'' E). The novel isolate was able to grow at 20-40 °C (optimum 33 °C), at pH 6.0-9.0 (optimum pH 7.0) and with 1.0-12.0 % (w/v) NaCl (optimum 3.0-5.0 %). Phylogenetic analysis based on 16S rRNA gene sequences indicated that the most closely related validly published species is Marinilabilia salmonicolor JCM 21150^T (96.0 % similarity). Average nucleotide identity, average amino acid identity, percentage of conserved proteins and digital DNA-DNA hybridization values between strain WTE16^T and Marinilabilia salmonicolor JCM 21150^T were 73.8 %, 73.5 %, 63.4 % and 19.5-24.2 %, respectively. The genomic DNA G+C content of strain WTE16^T was 40.8 mol%. Chemotaxonomic analysis showed that the sole respiratory quinone was menaquinone 7 (MK-7), and the major fatty acids included iso-C15 : 0 and anteiso-C15 : 0. The polar lipid profile of strain WTE16^T included phosphatidylethanolamine, three unidentified phospholipids and three unidentified lipids. On the basis of its phylogenetic, phenotypic, chemotaxonomic, genotypic and genomic characteristics, strain WTE16^T is suggested to represent a novel species of the genus Marinilabilia, for which the name Marinilabilia rubra sp. nov. is proposed. The type strain is WTE16^T (=KCTC 62599^T=MCCC 1H00311^T).