Huang, Zhaobin

A novel yellow-coloured bacterial strain MA10T was isolated from mangrove sediment and subjected to polyphasic taxonomic identification. Strain MA10T was Gram-negative, rod-shaped, catalase-positive and oxidase-positive. Carotenoid pigment was present, and flexirubin-type pigment was absent. The 16S rRNA gene of strain MA10T had the highest sequence similarity with Tamlana crocina HST1-43T of 94.5%. The genome size was 3.77 Mbp with a genomic G+C content of 36.3%. The phylogenetic analysis of the 16S rRNA gene sequence and whole-genome sequence showed that strain MA10T belonged to the genus Tamlana of the family Flavobacteriaceae and tightly clustered with T. crocina HST1-43T. The digital DNA–DNA hybridization value and average nucleotide identity value between strain MA10T and T. crocina HST1-43T were 20.4 and 76.7%, respectively. The major menaquinone was MK-6. The major fatty acids (>10 %) were iso-C15:0 (41.6%) and iso-C15:1 G (16.8%). The polar lipids consisted of phosphatidylethanolamine, two unidentified aminolipids and three unidentified lipids. Based on the present polyphasic taxonomic study, strain MA10T was considered to represent a novel species of the genus Tamlana, for which the name Tamlana flava sp. nov. was proposed. The type strain was MA10T (=MCCC 1K09289T=KCTC 102321T). Additionally, the phylogeny of the 16S rRNA gene and whole-genome sequences found that the hitherto described nine species of the genus Tamlana and Algibacter onchidii presented polyphyletic clades, which could be divided into five different genera. The average amino acid identity value of 80% was chosen as the boundary of the five genera. Thus, except for the genus Tamlana, four novel genera named Allotamlana gen. nov., Cognatitamlana gen. nov., Neotamlana gen. nov. and Pseudotamlana gen. nov. were proposed. This study provided valuable taxonomic analysis of the genus Tamlana.

Members of the class Opitutae are widely distributed in various environments such as rice paddy soil, freshwater lakes, seawater, marine sediment, and invertebrate digestive tracts. The class currently consists of two orders, Opitutales and Puniceicoccales, represented by the families Opitutaceae and Puniceicoccaceae, respectively, which are primarily delineated on the basis of 16S rRNA gene sequences and limited phenotypic characterizations of a few type strains. The scarcity of 16S rRNA gene and genome sequences generated from the type strains of the class Opitutae constrained our understanding of the ecological distribution and adequate resolution of its taxonomy. Here, an Opitutae strain designated WMMB3T, isolated from a mangrove sediment, was subjected to taxonomic characterization. The 16S rRNA gene of strain WMMB3T shared high sequence similarities with Coraliomargarita akajimensis DSM 45221T and C. sinensis WN38T of 96.1 and 95.9%, respectively. Phylogenetic analysis suggested that strain WMMB3T formed a monophyletic branch affiliated to the genus Coraliomargarita. The average nucleotide identity (ANI) values, digital DNA–DNA hybridization (dDDH) values and average amino acid identity (AAI) values of strain WMMB3T compared between Coraliomargarita members were 71.8–72.5, 20.7, and 68.2–68.7%, respectively, indicating that strain WMMB3T represented a novel species of Coraliomargarita. The genome of strain WMMB3T was 4.5 Mbp with a DNA G + C content of 56.0%. The respiratory quinone was menaquinone-7. The major fatty acids were iso-C14:0, and C18:1ω9c. Based on genomic, phenotypic, and chemotaxonomic characterizations, strain WMMB3T represents a novel species, and Coraliomargarita parva sp. nov. is proposed. Additionally, the phylogenomic analysis of more than 500 genomes of the class Opitutae, encompassing a majority of uncultivated bacteria and a few type strains, was performed using the Genome Taxonomic Database toolkit (GTDB-Tk) to present adequate resolution of the taxonomy. Combined with 16S rRNA gene sequence phylogeny and genomic relatedness, five novel families retrieved mainly from marine habitats were proposed: Coraliomargaritaceae fam. nov., Pelagicoccaceae fam. nov., Cerasicoccaeae fam. nov., Oceanipulchritudinaceae fam. nov., and Alterococcaeae fam. nov. AAI values of 58–60% could be considered as the boundary to delineate families of the class Opitutae. This study provided a new taxonomic framework of the class Opitutae based on the genomic data.

The shrimp Rimicaris exoculata represents the dominant faunal biomass at many deep-sea hydrothermal vent ecosystems along the Mid-Atlantic Ridge. This organism harbors dense bacterial epibiont communities in its enlarged cephalothoracic chamber that play an important nutritional role. Deltaproteobacteria are ubiquitous in epibiotic communities of R. exoculata , and their functional roles as epibionts are based solely on the presence of functional genes. Here, we describe “ Candidatus Desulfobulbus rimicarensis,” an uncultivated deltaproteobacterial epibiont. Compared to campylobacterial and gammaproteobacterial epibionts of R. exoculata , this bacterium possessed unique metabolic pathways, such as the Wood-Ljungdahl pathway, as well as sulfur disproportionation and nitrogen fixation pathways. Furthermore, this epibiont can be distinguished from closely related free-living Desulfobulbus strains by its reduced genetic content and potential loss of functions, suggesting unique adaptations to the shrimp host. This study is a genomic and transcriptomic analysis of a deltaproteobacterial epibiont and largely expands the understanding of its metabolism and adaptation to the R. exoculata host.