Faecalibacterium taiwanense sp. nov., isolated from human faeces.

Two Gram-stain-negative, straight rods, non-motile, asporogenous, catalase-negative and obligately anaerobic butyrate-producing strains, HLW78T and CYL33, were isolated from faecal samples of two healthy Taiwanese adults. Phylogenetic analyses of 16S rRNA and DNA mismatch repair protein MutL (mutL) gene sequences revealed that these two novel strains belonged to the genus Faecalibacterium. On the basis of 16S rRNA and mutL gene sequence similarities, the type strains Faecalibacterium butyricigenerans AF52-21T(98.3-98.1 % and 79.0-79.5 % similarity), Faecalibacterium duncaniae A2-165T(97.8-97.9 % and 70.9-80.1 %), Faecalibacterium hattorii APC922/41-1T(97.1-97.3 % and 80.3-80.5 %), Faecalibacterium longum CM04-06T(97.8-98.0% and 78.3 %) and Faecalibacterium prausnitzii ATCC 27768T(97.3-97.4 % and 82.7-82.9 %) were the closest neighbours to the novel strains HLW78T and CYL33. Strains HLW78T and CYL33 had 99.4 % both the 16S rRNA and mutL gene sequence similarities, 97.9 % average nucleotide identity (ANI), 96.3 % average amino acid identity (AAI), and 80.5 % digital DNA-DNA hybridization (dDDH) values, indicating that these two strains are members of the same species. Phylogenomic tree analysis indicated that strains HLW78T and CYL33 formed an independent robust cluster together with F. prausnitzii ATCC 27768T. The ANI, AAI and dDDH values between strain HLW78T and its closest neighbours were below the species delineation thresholds of 77.6-85.1 %, 71.4-85.2 % and 28.3-30.9 %, respectively. The two novel strains could be differentiated from the type strains of their closest Faecalibacterium species based on their cellular fatty acid compositions, which contained C18 : 1 ω7c and lacked C15 : 0 and C17 : 1 ω6c, respectively. Phenotypic, chemotaxonomic and genotypic test results demonstrated that the two novel strains HLW78T and CYL33 represented a single, novel species within the genus Faecalibacterium, for which the name Faecalibacterium taiwanense sp. nov. is proposed. The type strain is HLW78T (=BCRC 81397T=NBRC 116372T).

Microbial decomposition of biodegradable plastics on the deep-sea floor.

Microbes can decompose biodegradable plastics on land, rivers and seashore. However, it is unclear whether deep-sea microbes can degrade biodegradable plastics in the extreme environmental conditions of the seafloor. Here, we report microbial decomposition of representative biodegradable plastics (polyhydroxyalkanoates, biodegradable polyesters, and polysaccharide esters) at diverse deep-sea floor locations ranging in depth from 757 to 5552 m. The degradation of samples was evaluated in terms of weight loss, reduction in material thickness, and surface morphological changes. Poly(L-lactic acid) did not degrade at either shore or deep-sea sites, while other biodegradable polyesters, polyhydroxyalkanoates, and polysaccharide esters were degraded. The rate of degradation slowed with water depth. We analysed the plastic-associated microbial communities by 16S rRNA gene amplicon sequencing and metagenomics. Several dominant microorganisms carried genes potentially encoding plastic-degrading enzymes such as polyhydroxyalkanoate depolymerases and cutinases/polyesterases. Analysis of available metagenomic datasets indicated that these microorganisms are present in other deep-sea locations. Our results confirm that biodegradable plastics can be degraded by the action of microorganisms on the deep-sea floor, although with much less efficiency than in coastal settings.

Arthrobacter mangrovi sp. nov., an actinobacterium isolated from the rhizosphere of a mangrove.

A novel actinobacterium, designated HIs16-36T, was isolated from the rhizosphere of a mangrove on Ishigaki Island, Okinawa, Japan, and its taxonomic position was investigated using a polyphasic approach. Phylogenetic analysis based on 16S rRNA gene sequence comparisons revealed that strain HIs16-36T was closely related to the members of the genus Arthrobacter. The highest 16S rRNA gene sequence similarity was observed with Arthrobacter crystallopoietes (98.5 %), followed by Arthrobacter globiformis (97.2 %). The peptidoglycan of strain HIs16-36T was of the A4α type, with lysine as the diagnostic diamino acid. The predominant isoprenoid quinone was MK-9(H2) and the major fatty acids were anteiso-C15 : 0 and iso-C15 : 0. The polar lipids were identified as diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol and two glycolipids. These chemotaxonomic features corresponded to those of the genus Arthrobacter. Meanwhile, the differences in some phenotypic characteristics, along with the results of average nucleotide identity and digital DNA-DNA hybridization analyses, indicated that strain HIs16-36T should be distinguished from the recognized species of the genus Arthrobacter. Therefore, strain HIs16-36T represents a novel species of the genus Arthrobacter, for which the name Arthrobacter mangrovi sp. nov. is proposed. The type strain is HIs16-36T (=NBRC 112813T=TBRC 15750T).