Extensive genomic study characterizing three Paracoccaceae populations and revealing Pseudogemmobacter lacusdianii sp. nov. and Paracoccus broussonetiae sp. nov

Bacteria within the family Paracoccaceae show promising potential for applications in various fields, garnering significant research attention. Three Gram stain-negative bacteria, strains CPCC 101601T, CPCC 101403T, and CPCC 100767, were isolated from diverse environments: freshwater, rhizosphere soil of Broussonetia papyrifera, and the phycosphere, respectively. Analysis of their 16S rRNA gene sequences, compared with those in the GenBank database, indicated that they belong to the family Paracoccaceae, with nucleotide similarities of 92.5%-99.9% to all of the Paracoccaceae members with valid taxonomic names. Phylogenetic studies based on 16S rRNA gene and whole-genome sequences identified CPCC 101601T as a member of the genus Pseudogemmobacter, CPCC 101403T belonging to the genus Paracoccus, and CPCC 100767 as part of the genus Gemmobacter. Notably, genomic analysis using average nucleotide identity (ANI; <95%) and digital DNA-DNA hybridization (dDDH; <70%) with their closely related strains suggested that CPCC 101601T and CPCC 101403T represent new species within their respective genera. Conversely, CPCC 100767 exhibited high ANI (98.5%) and dDDH (87.4%) values with Gemmobacter fulvus con5T, indicating it belongs to this already recognized species. The in-depth genomic analysis revealed that strains CPCC 101601T, CPCC 101403T, and CPCC 100767 harbor key genes related to the pathways for denitrifying, MA utilization, and polyhydroxyalkanoate biosynthesis. Moreover, genotyping and phenotyping analysis confirmed that strain CPCC 100767 has the ability to convert atmospheric nitrogen into ammonia and produce 5-aminolevulinic acid, whereas CPCC 101601T can only perform the former bioprocess.IMPORTANCEBased on polyphasic taxonomic study, two new species, Pseudogemmobacter lacusdianii and Paracoccus broussonetiae, affiliated with the family Paracoccaceae were identified. This expands our understanding of the family Paracoccaceae and provides new microbial materials for further studies. Modern genomic techniques such as average nucleotide identity and digital DNA-DNA hybridization were utilized to determine species affiliations. These methods offer more precise results than traditional classification mainly based on 16S rRNA gene analysis. Beyond classification of these strains, the research delved into their genomes and discovered key genes related to denitrification, MA utilization, and polyhydroxyalkanoate biosynthesis. The identification of these genes provides a molecular basis for understanding the environmental roles of these strains. Particularly, strain CPCC 100767 demonstrated the ability to convert atmospheric nitrogen into ammonia and produce 5-aminolevulinic acid. These bioprocess capabilities are of significant practical value, such as in agricultural production for use as biofertilizers or biostimulants.

Mesobacterium hydrothermale sp. nov., isolated from shallow-sea hydrothermal systems off Kueishantao Island

A Gram-negative, rod-shaped, non-motile, aerobic bacterium, designated as strain TK19101T, was isolated from the intermediate seawater of yellow vent in the shallow-sea hydrothermal system located near Kueishantao Island. The strain was found to grow at 10-40 °C (optimum, 35 °C), at pH 6.0-8.0 (optimum, 7.0), and in 0-5% (w/v) NaCl (optimum, 1%). Strain TK19101T was catalase-positive and oxidase-positive. The predominant fatty acids (> 10%) in strain TK19101T cells were C16:0, summed feature 8 (C18:1 ω6c and/or C18:1 ω7c), and C18:0. The predominant isoprenoid quinone of strain TK19101T was ubiquinone-10. The polar lipids of strain TK19101T comprised phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, phospholipid, and unknown polar lipid. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain TK19101T belonged to the genus Mesobacterium. Strain TK19101T exhibited highest 16S rRNA gene sequence similarity value to Mesobacterium pallidum MCCC M24557T (97.48%). The estimated average nucleotide identity and digital DNA-DNA hybridization values between strain TK19101T and the closest related species Mesobacterium pallidum MCCC M24557T were 74.88% and 20.30%, respectively. The DNA G + C content was 63.49 mol%. On the basis of the analysis of 16S rRNA gene sequences, genotypic and phylogenetic data, strain TK19101T has a unique phylogenetic status and represents a novel species of genus Mesobacterium, for which the name Mesobacterium hydrothermale sp. nov. is proposed. The type strain is TK19101T (= MCCC 1K08936T = KCTC 8354T).

Phyllobacteriaceae: a family of ecologically and metabolically diverse bacteria with the potential for different applications

The family Phyllobacteriaceae is a heterogeneous assemblage of more than 146 species of bacteria assigned to its existing 18 genera. Phylogenetic analyses have shown great phylogenetic diversity and also suggested about incorrect classification of several species that need to be reassessed for their proper phylogenetic classification. However, almost 50% of the family members belong to the genus Mesorhizobium only, of which the majority are symbiotic nitrogen fixers associated with different legumes. Other major genera are Phyllobacterium, Nitratireductor, Aquamicrobium, and Aminobacter. Nitrogen-fixing, legume nodulating members are present in Aminobacter and Phyllobacterium as well. Aquamicrobium spp. can degrade environmental pollutants, like 2,4-dichlorophenol, 4-chloro-2-methylphenol, and 4-chlorophenol. Chelativorans, Pseudaminobacter, Aquibium, and Oricola are the other genera that contain multiple species having diverse metabolic capacities, the rest being single-membered genera isolated from varied environments. In addition, heavy metal and antibiotic resistance, chemolithoautotrophy, poly-β-hydroxybutyrate storage, cellulase production, etc., are the other notable characteristics of some of the family members. In this report, we have comprehensively reviewed each of the species of the family Phyllobacteriaceae in their eco-physiological aspects and found that the family is rich with ecologically and metabolically highly diverse bacteria having great potential for human welfare and environmental clean-up.

Genomic potential for inorganic carbon sequestration and xenobiotic degradation in marine bacterium Youngimonas vesicularis CC-AMW-ET affiliated to family Paracoccaceae

Ecological studies on marine microbial communities largely focus on fundamental biogeochemical processes or the most abundant constituents, while minor biological fractions are frequently neglected. Youngimonas vesicularis CC-AMW-ET, isolated from coastal surface seawater in Taiwan, is an under-represented marine Paracoccaceae (earlier Rhodobacteraceae) member. The CC-AMW-ET genome was sequenced to gain deeper insights into its role in marine carbon and sulfur cycles. The draft genome (3.7 Mb) contained 63.6% GC, 3773 coding sequences and 51 RNAs, and displayed maximum relatedness (79.06%) to Thalassobius litoralis KU5D5T, a Roseobacteraceae member. While phototrophic genes were absent, genes encoding two distinct subunits of carbon monoxide dehydrogenases (CoxL, BMS/Form II and a novel form III; CoxM and CoxS), and proteins involved in HCO3- uptake and interconversion, and anaplerotic HCO3- fixation were found. In addition, a gene coding for ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO, form II), which fixes atmospheric CO2 was found in CC-AMW-ET. Genes for complete assimilatory sulfate reduction, sulfide oxidation (sulfide:quinone oxidoreductase, SqrA type) and dimethylsulfoniopropionate (DMSP) cleavage (DMSP lyase, DddL) were also identified. Furthermore, genes that degrade aromatic hydrocarbons such as quinate, salicylate, salicylate ester, p-hydroxybenzoate, catechol, gentisate, homogentisate, protocatechuate, 4-hydroxyphenylacetic acid, N-heterocyclic aromatic compounds and aromatic amines were present. Thus, Youngimonas vesicularis CC-AMW-ET is a potential chemolithoautotroph equipped with genetic machinery for the metabolism of aromatics, and predicted to play crucial roles in the biogeochemical cycling of marine carbon and sulfur.

Oricola nitratireducens sp. nov., a novel nitrate reducing bacterium isolated from marine sediment in East China Sea

A novel strain designated NBU1457^T, was isolated from marine sediment sampled on Meishan Island located in the East China Sea. Cells of strain NBU1457^T was Gram-negative, facultatively anaerobic, non-motile and ovoid-shaped. Strain NBU1457^T grew optimally at 37 °C, NaCl concentration of 2.0-3.0% (w/v) and pH 6.5-7.5. Catalase and oxidase activities, urease, nitrate reduction and H₂S production were positive. Indole production, methyl red reaction, hydrolysis of starch, gelatin, casein, Tweens 20, 40, 60 and 80 were negative. Comparative analysis of the 16S rRNA gene sequence showed highest similarities to the species with validated name Oricola thermophila MEBiC13590^T (98.8%), Oricola cellulosilytica CC-AMH-0 ^T (97.9%) and Oricola indica JL-62 ^T (97.9%). Phylogenetic analyses indicated that strain NBU1457^T clustered with the genus Oricola and closely related to strains Oricola thermophila MEBiC13590^T, Oricola cellulosilytica CC-AMH-0 ^T and Oricola indica JL-62 ^T. The average nucleotide identity and digital DNA-DNA hybridization values between strain NBU1457^T and related species of genus Oricola were well below the threshold limit for prokaryotic species delineation. The DNA G + C content was 63.2%. The major cellular fatty acid was summed feature 8 (C_18:1 ω7c and/or C_18:1 ω6c). The major polar lipids were phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylmonomethylethanolamine, sulfoquinovosyldiacylglycerol and phosphatidylglycerol. The only respiratory quinone was ubiquinone-10 (Q-10). Combining results of our phenotypic, chemotaxonomic and genotypic data, strain NBU1457^T is considered to be a representative in the genus Oricola, which the name Oricola nitratireducens sp. nov. is proposed. The type strain of the new species is NBU1457^T (= KCTC 82225 ^T = MCCC 1K04764^T).

Gymnodinialimonas phycosphaerae sp. nov., a phycosphere bacterium isolated from Karlodinium veneficum

A facultative anaerobic, Gram-negative, non-motile, rod-shaped bacterial strain, designated N5^T, was obtained from the phycosphere microbiota of the marine planktonic dinoflagellate, Karlodinium veneficum. Strain N5^T showed growth on marine agar at 25 °C, pH 7 and 1 % (w/v) NaCl and produced a yellow colour. According to a phylogenetic study based on 16S rRNA gene sequences, strain N5^T has a lineage within the genus Gymnodinialimonas. The G+C content in the genome of strain N5^T is 62.9 mol% with a total length of 4 324 088 bp. The NCBI Prokaryotic Genome Annotation Pipeline revealed that the N5^T genome contained 4230 protein-coding genes and 48 RNA genes, including a 5S rRNA, 16S rRNA, 23S rRNA, 42 tRNA, and three ncRNAs. Genome-based calculations (genome-to-genome distance, average nucleotide identity and DNA G+C content) clearly indicated that the isolate represents a novel species within the genus Gymnodinialimonas. The predominant fatty acids were C_19 : 0 cyclo ω8c and feature 8 (comprising C_18 : 1 ω6c and/or C_18 : 1 ω7c). The major polar lipids were phosphatidylglycerol, phosphatidylethanolamine and phosphatidylcholine. The main respiratory quinone was Q-10. Based on its phenotypic, phylogenetic, genomic and chemotaxonomic features, strain N5^T represents a novel species of the genus Gymnodinialimonas, for which the name Gymnodinialimonas phycosphaerae sp. nov. is proposed. The type strain is N5^T (=KCTC 82362^T=NBRC 114899^T).

Limibaculum sediminis sp. nov., isolated from mangrove sediment

A Gram-stain-negative, cream-coloured, aerobic, motile and ovoid- to rod-shaped bacterium, designated as FT325^T, was isolated from mangrove sediment collected in Shenzhen, PR China. The taxonomic position of strain FT325^T was established by phylogenetic, physiological, biochemical and chemotaxonomic analyses. Strain FT325^T grew optimally at 37-40 °C and pH 6.0 in the presence of 0 % (w/v) NaCl. Results of 16S rRNA gene sequence analysis showed that strain FT325^T was most similarly related to Limibaculum halophilum CAU 1123^T (96.2 %), Phaeovulum vinaykumarii DSM 18714^T (93.9%) and Amaricoccus solimangrovi HB 172011^T (93.7 %). The major fatty acids (>10 %) were C_18 : 1  ω7c (60.0 %) and 11-methyl C_18 : 1  ω7c (16.7 %). The sole respiratory quinone was Q-10. The polar lipids were phosphatidylglycerol, one unidentified glycolipid, three unidentified aminolipids and three unidentified phospholipids. Its estimated genome size was 4 318 768 bp and the genomic DNA G+C content was 69.6 mol%. Based on its distinct phenotypic, chemotaxonomic and phylogenetic characteristics, strain FT325^T represents a novel species of the genus Limibaculum, for which the name Limibaculum sediminis sp. nov. is proposed (=MCCC 1K07397^T=KCTC 92313^T).