Flammeovirga pectinis sp. nov., isolated from the gut of the Korean scallop, Patinopecten yessoensis

Discovery of two novel Flavobacterium species with potential for complex polysaccharide degradation

Polysaccharides are recognized for their extensive biological functions, holding significant promise for applications in both medicine and food industries. However, their utilization is frequently constrained by challenges such as high molecular weights and indistinct sugar chain structures. Recently, two novel bacterial strains, N6T and J3T, were isolated from the Nakdong River in Korea. These strains, which belong to the phylum Bacteroidota, are Gram-stain-negative, non-motile, aerobic, rod-shaped bacteria and have shown polysaccharide-degrading capabilities. Through comprehensive analyses, including 16S rRNA gene sequencing, whole-genome sequencing, and detailed morphological, physiological, and chemotaxonomic characterizations, these strains have been identified as new species within the genus Flavobacterium. KEGG pathway analysis further confirmed their robust capabilities for carbohydrate utilization. Additional investigations using the dbCAN and dbCAN-PUL databases identified the presence of carbohydrate-hydrolyzing enzymes (CAZymes) and polysaccharide utilization loci (PULs) within these strains, suggesting their potential to degrade various polysaccharides. Subsequent in vitro growth experiments demonstrated that strains N6T and J3T can degrade chitin, β-glucan, κ-carrageenan, and cellulose. Given their diverse polysaccharide degradation abilities, these strains are formally proposed to be named Flavobacterium polysaccharolyticum sp. nov. and Flavobacterium aureirubrum sp. nov. The type strains are designated as N6T (= KCTC 102173T = GDMCC 1.4609T) and J3T (= KCTC 102172T = GDMCC 1.4608T), respectively.

Three novel marine species of the genus Reichenbachiella exhibiting degradation of complex polysaccharides

Three novel strains designated ABR2-5T, BKB1-1T, and WSW4-B4T belonging to the genus Reichenbachiella of the phylum Bacteroidota were isolated from algae and mud samples collected in the West Sea, Korea. All three strains were enriched for genes encoding up to 216 carbohydrate-active enzymes (CAZymes), which participate in the degradation of agar, alginate, carrageenan, laminarin, and starch. The 16S rRNA sequence similarities among the three novel isolates were 94.0%-94.7%, and against all three existing species in the genus Reichenbachiella they were 93.6%-97.2%. The genome sizes of the strains ABR2-5T, BKB1-1T, and WSW4-B4T were 5.5, 4.4, and 5.0 Mb, respectively, and the GC content ranged from 41.1%-42.0%. The average nucleotide identity and the digital DNA-DNA hybridization values of each novel strain within the isolates and all existing species in the genus Reichenbachiella were in a range of 69.2%-75.5% and 17.7-18.9%, respectively, supporting the creation of three new species. The three novel strains exhibited a distinctive fatty acid profile characterized by elevated levels of iso-C15:0 (37.7%-47.4%) and C16:1 ω5c (14.4%-22.9%). Specifically, strain ABR2-5T displayed an additional higher proportion of C16:0 (13.0%). The polar lipids were phosphatidylethanolamine, unidentified lipids, aminolipids, and glycolipids. Menaquinone-7 was identified as the respiratory quinone of the isolates. A comparative genome analysis was performed using the KEGG, RAST, antiSMASH, CRISPRCasFinder, dbCAN, and dbCAN-PUL servers and CRISPRcasIdentifier software. The results revealed that the isolates harbored many key genes involved in central metabolism for the synthesis of essential amino acids and vitamins, hydrolytic enzymes, carotenoid pigments, and antimicrobial compounds. The KEGG analysis showed that the three isolates possessed a complete pathway of dissimilatory nitrate reduction to ammonium (DNRA), which is involved in the conservation of bioavailable nitrogen within the ecosystem. Moreover, all the strains possessed genes that participated in the metabolism of heavy metals, including arsenic, copper, cobalt, ferrous, and manganese. All three isolated strains contain the class 2 type II subtype C1 CRISPR-Cas system in their genomes. The distinguished phenotypic, chemotaxonomic, and genomic characteristics led us to propose that the three strains represent three novel species in the genus Reichenbachiella: R. ulvae sp. nov. (ABR2-5T = KCTC 82990T = JCM 35839T), R. agarivorans sp. nov. (BKB1-1T = KCTC 82964T = JCM 35840T), and R. carrageenanivorans sp. nov. (WSW4-B4T = KCTC 82706T = JCM 35841T).

Fluviispira vulneris sp. nov., isolated from human wound secretions

Human infections by environmental bacteria is becoming an increasing problem and has become a matter of great concern due to the adverse effects worldwide. In this study, we reported a new environmental pathogen. Isolate GX5518T was a novel Gram-negative, aerobic, non-motile, pleomorphic and red-pigmented bacterium, was isolated from human wound secretions (GuangXi, People's Republic of China). Growth occurred at pH 6.0-8.0 (optimum, pH 7.0) and 10-37 °C (optimum, 28-32 °C) with 0-1.5% (w/v) NaCl in R2A agar. Comparative analysis of the 16S rRNA gene sequences revealed that isolate GX5518T was closely related to Fluviispira sanaruensis JCM 31447T (99.73%) and Fluviispira multicolorata 33A1-SZDPT (98.49%). However, the estimated ANI values of the isolate GX5518T compared to the F. sanaruensis JCM 31447T and F. multicolorata 33A1-SZDPT were 88.67% and 77.35%, respectively. The estimated dDDH, ANI and AAI values between isolate GX5518T and its closely related strains were below the threshold values generally considered for recognizing a new species. The genome size was 3.6 Mbp and the DNA G + C content was 33.1%. The predominant fatty acids (> 5%) in GX5518T cells were iso-C15:0, C16:0, C17:0, C17:1 ω8c and C16:1 ω7c/C16:1 ω6c. The major menaquinone was MK-8 (86.9%). The polar lipids were phosphatidylethanolamine (PE), phosphatidylglycerol (PG) and three unknown lipids (L1-3). The chemical composition was different from that of the F. sanaruensis JCM 31447T. Comparative genomics analysis between isolate GX5518T and its related strains revealed that there were a number of genes involved in resistance to antibiotics and toxic compounds in isolate GX5518T, which were responsible for the copper homeostasis, cobalt-zinc-cadmium resistance, resistance to fluoroquinolones, and zinc resistance. Based on the phenotypic, chemotaxonomic, and genomic analyses, isolate GX5518T (= CGMCC 1.18685T = KCTC 82149T) represents a novel species of the genus Fluviispira, for which the name Fluviispira vulneris sp. nov. is proposed.

Chitinolyticbacter albus sp. Nov., A Novel Chitin-Degrading Bacterium Isolated from Ancient Wood Rhizosphere Soil

In this study, a novel aerobic mesophilic bacterial strain with capable of degrading chitin, designated YIM B06366^T, was isolated and classified. The rod-shaped, Gram-stain-negative, on-spore-forming bacterium originated from rhizosphere soil sample collected in Kunming City, Yunnan Province, southwest PR China. Strain YIM B06366^T exhibited growth at temperatures between 20 and 35 °C (optimum, 30 °C) and at pH 6.0-8.0 (optimum, pH 6.0). The analysis of 16S rRNA gene sequence similarity revealed that strain YIM B06366^T was most closely related to type strain Chitinolyticbacter meiyuanensis SYBC-H1^T (98.9%). Phylogenetic analysis based on genome data indicated that strain YIM B06366^T should be assigned to the genus Chitinolyticbacter. The Average Nucleotide Identity (ANI) and digital DNA-DNA Hybridization (dDDH) values between strain YIM B06366^T and the reference strain Chitinolyticbacter meiyuanensis SYBC-H1^T were 84.4% and 27.7%, respectively. The major fatty acids included Summed Feature 3 (C_16:1 ω6c/C_16:1 ω7c), Summed Feature 8 (C_18:1 ω6c/C_18:1 ω7c), and C_16:0. The polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, aminophospholipids, and two unidentified phospholipids. The predominant menaquinone was Q-8, and the genomic DNA G + C content was 64.1%. Considering the polyphasic taxonomic evidence, strain YIM B06366^T is proposed as a novel species within the genus Chitinolyticbacter, named Chitinolyticbacter albus sp. nov. (type strain YIM B06366^T = KCTC 92434^T = CCTCC AB 2022163^T).

An Update on Novel Taxa and Revised Taxonomic Status of Bacteria (Including Members of the Phylum Planctomycetota) Isolated from Aquatic Host Species Described in 2018 to 2021

Increased interest in farmed aquatic species, aquatic conservation measures, and microbial metabolic end-product utilization have translated into a need for awareness and recognition of novel microbial species and revisions to bacterial taxonomy. Because this need has largely been unmet, through a 4-year literature review, we present lists of novel and revised bacterial species (including members of the phylum Planctomycetota) derived from aquatic hosts that can serve as a baseline for future biennial summaries of taxonomic revisions in this field. Most new and revised taxa were noted within oxidase-positive and/or nonglucose fermentative Gram-negative bacilli, including members of the Tenacibaculum, Flavobacterium, and Vibrio genera. Valid and effectively published novel members of the Streptococcus, Erysipelothrix, and Photobacterium genera are additionally described from disease pathogenesis perspectives.

Marinigracilibium pacificum gen. nov., sp. nov., a starch-degrading bacterium isolated from tropical western Pacific

The Gram-stain-negative, golden-yellow-colored, non-spore-forming, strictly aerobic, slender rod-shaped bacterial strain, designated KN852^T, was isolated from a seamount in the tropical western Pacific. The predominant respiratory quinone was MK-7 and the polar lipid profiles contained phosphatidylethanolamine, one unidentified phospholipid and six unidentified polar lipids. The predominant cellular fatty acids were iso-C_15:0, summed feature 3(C_16:1ω7c and/or iso-C_15:0 2OH), iso-C_17:0 3OH and iso-C_15:1 G. Phylogenetic analyses of 16S rRNA gene sequence revealed that strain KN852^T was affiliated with the family Flammeovirgaceae of the phylum Bacteroidota and formed a distinct lineage. The genomic DNA G + C content of strain KN852^T was 34.8%. Collectively, based on phenotypic, chemotaxonomic, phylogenetic and genomic evidence presented, strain KN852^T represents a novel species of a novel genus of the family Flammeovirgaceae, for which the name Marinigracilibium pacificum gen. nov., sp. nov. is proposed. The type strain is KN852^T (= CGMCC 1.17119^T = KCTC 72433^T).

The Second Chromosome Promotes the Adaptation of the Genus Flammeovirga to Complex Environments

Approximately 10% of bacterial strains contain more than one chromosome; however, in contrast to the primary chromosomes, the mechanisms underlying the formation of the second chromosomes and the significance of their existence remain unclear. Species of the genus Flammeovirga are typical polysaccharide-degrading bacteria, and herein, we report complete genome maps of this genus. These genomes all had multireplicons and second chromosomes. The second chromosome, much larger than plasmids and even megaplasmids, had rRNA and a disparity of 1% relative to the main chromosome in guanine-cytosine (GC) content. The largest chromosomes carried core genes for cellular processes, while the second chromosomes were enriched with genes involved in the transport and metabolism of inorganic ions and carbohydrates, particularly genes encoding glycoside hydrolases and polysaccharide lyases, which constituted the genetic basis for the strains’ excellent capabilities to utilize polysaccharides. The second chromosomal evolution had a higher mutation rate than the primary chromosomes. Furthermore, the second chromosomes were also enriched in horizontal transfer genes and duplicated genes. The primary chromosomes were more evolutionarily conserved, while the second chromosomes were more plastic, which might be related to their different roles in the bacterial survival process. This study can be used as an example to explain possible formation mechanisms and functions of the second chromosomes, providing a reference for peer research on the second chromosomes. In particular, the second chromosomes were enriched in polysaccharide-degrading enzymes, which will provide theoretical support for using genomic data to mine tool-type carbohydrase resources.

IMPORTANCE For decades, the typical bacterial genome has been thought to contain a single chromosome and a few small plasmids carrying nonessential genes. However, an increasing number of secondary chromosomes have been identified in various bacteria (e.g., plant symbiotic bacteria and human pathogens). This study reported three complete genomes of the polysaccharide-degrading marine bacterial genus Flammeovirga, revealed that they harbor two chromosomes, and further identified that the presence of a multireplicon system is a characteristic of complete Flammeovirga genomes. These sequences will add to our knowledge on secondary chromosomes, especially within Bacteroidetes. This study indicated that the second chromosomes of the genus Flammeovirga initially originated from an ancestral plasmid and subsequently expanded by gene duplication or by obtaining heterologous genes with functions, thus promoting host strains to adapt to complex living environments (e.g., to degrade more diverse polysaccharides from marine environments). These findings will promote the understanding of the evolution and function of bacteria with multireplicon systems.

Flammeovirga agarivorans sp. nov., an agar-digesting marine bacterium isolated from surface seawater

A Gram-stain-negative, aerobic, gliding, reddish-orange-coloured, rod-shaped strain, designated SR4^T, was isolated from surface seawater sampled at Luhuitou fringing reef (South China Sea). Phylogenetic analyses based on the 16S rRNA gene, phylogenomic analysis of single-copy gene families and whole genome data affiliated it to the genus Flammeovirga. It was most closely related to Flammeovirga yaeyamensis NBRC 100898^T (97.99 % 16S rRNA gene similarity). The genome average nucleotide identity and DNA-DNA relatedness values between strain SR4^T and its reference strains were less than 74.2 and 16.3 %, respectively. Growth occurred at 20-35 °C (optimum, 28 °C), pH 6.0-9.0 (optimum, pH 7.0) and in the presence of 1-6 % (w/v) NaCl (optimum, 2-4 %). The dominant fatty acids were C_16 : 0, iso-C_15 : 0 and C_20 : 4  ω6,9,12,15c. The polar lipid profile of strain SR4^T comprised phosphatidylethanolamine, two glycolipids, two aminophospholipids and three unidentified lipids. The major respiratory quinone was MK-7. The DNA G+C content of strain SR4^T was 34.20 mol%. On the basis of the polyphasic evidence, strain SR4^T is proposed as representing a novel species of the genus Flammeovirga, for which the name Flammeovirga agarivorans sp. nov. is proposed. The type strain is SR4^T (=KCTC 82075^T=MCCC 1A17137^T).