Roseitalea porphyridii gen. nov., sp. nov., isolated from a red alga, and reclassification of Hoeflea suaedae Chung et al. 2013 as Pseudohoeflea suaedae gen. nov., comb. nov

Pseudohoeflea coraliihabitans sp. nov., a poly-β-hydroxybutyrate-producing, halotolerant bacterium isolated from coral sediment in the Dapeng peninsula (Guangdong, China)

A Gram-stain-negative, strictly aerobic, motile, flagellated, rod-shaped, halotolerant, and poly-β-hydroxyalkanoate-producing bacterium, designated DP4N28-3T, was isolated from offshore sediment surrounding hard coral in the Dapeng peninsula (Guangdong, PR China). Growth occurred at 15-35 °C (optimal at 30 °C), pH 6.0-9.5 (optimal at 6.0-7.0), and 0.0-30.0 % NaCl concentration (w/v, optimal at 0.0-2.0 %), showing halotolerance. Phylogeny based on 16S rRNA gene sequences, five housekeeping genes, and genome sequences identified Pseudohoeflea suaedae DSM 23348T (98.1 %, 16S rRNA gene sequence similarity) as the most related species to strain DP4N28-3T. Average nucleotide identity, digital DNA-DNA hybridization, and average amino acid identity values between strain DP4N28-3T and P. suaedae DSM 23348T were all below the threshold of species demarcation. Major phenotypic differences were the flagella type and the limited sources of single carbon utilization by strain DP4N28-3T, which only included acetic acid, acetoacetic acid, d-glucuronic acid, and glucuronamide. Strain DP4N28-3T harboured the class I poly-β-hydroxyalkanoate synthase gene (phaC) and produced poly-β-hydroxybutyrate. The fatty acids were summed feature 8 (C18 : 1  ω6c and/or C18 : 1  ω7c, 49.4 %) and C16 : 0 (13.4 %). The major cellular polar lipids consisted of phosphatidylcholine, phosphatidylethanolamine, phosphatidylmonomethylethanolamine, phosphatidylglycerol, and sulfoquinovosyl diacylglycerol. The respiratory quinone was Q-10. The results of the phylogenetic, genomic, phenotypic, and chemotaxonomic analysis indicated that the isolated strain represents the type strain of a novel species. Based on these results, strain DP4N28-3T (=MCCC 1K05639T=KCTC 82803T) is proposed as the type strain of the novel species Pseudohoeflea coraliihabitans sp. nov.

Functional diversity of bacterial microbiota associated with the toxigenic benthic dinoflagellate Prorocentrum

Interactions between bacterial microbiota and epibenthic species of the dinoflagellate Prorocentrum may define the onset and persistence of benthic harmful algal blooms (bHABs). Chemical ecological interactions within the dinoflagellate phycosphere potentially involve a complex variety of organic molecules, metabolites, and toxins, including undefined bioactive compounds. In this study, the bacterial diversity and core members of the dinoflagellate-associated microbiota were defined from 11 strains of three epibenthic Prorocentrum species, representing three geographically disjunct locations within Mexican coastal waters. Microbiota profiles in stable monoclonal Prorocentrum cultures were obtained by sequencing amplicons of the V3-V4 region of the 16S rRNA gene. Thirteen classes of bacteria were identified among dinoflagellate clones, where Alphaproteobacteria, Gammaproteobacteria, and Bacteroidia were consistently dominant. The bacterial community structure exhibited significantly different grouping by the location of origin of dinoflagellate clones. No significant diversity difference was found among free-living or unattached bacteria in the dinoflagellate culture medium (M) compared with those in closer association with the dinoflagellate host cells (H). Twelve taxa were defined as core members of the bacterial assemblage, representing the genera Algiphilus, Cohaesibacter, Labrenzia, Mameliella, Marinobacter, Marivita, Massilia, Muricauda, Roseitalea, and an unclassified member of the Rhodobacteraceae. The core members are inferred to significantly contribute to primary and secondary metabolic functions, but no direct correlation with dinoflagellate toxigenicity was apparent. Overall the bacterial profile and implied gene functionality indicated a suite of positive interactions, suggesting either mutualism or commensalism with the dinoflagellate. The further characterization and interpretation of specific gene functions and interactions between bacteria and dinoflagellates, such as epibenthic members of genus Prorocentrum, are key to understanding their role in toxigenesis and bHAB development.

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.

Assessing the contribution of bacteria to the heat tolerance of experimentally evolved coral photosymbionts

Coral reefs are extremely vulnerable to ocean warming, which triggers coral bleaching-the loss of endosymbiotic microalgae (Symbiodiniaceae) from coral tissues, often leading to death. To enhance coral climate resilience, the symbiont, Cladocopium proliferum was experimentally evolved for >10 years under elevated temperatures resulting in increased heat tolerance. Bacterial 16S rRNA gene metabarcoding showed the composition of intra- and extracellular bacterial communities of heat-evolved strains was significantly different from that of wild-type strains, suggesting bacteria responded to elevated temperatures, and may even play a role in C. proliferum thermal tolerance. To assess whether microbiome transplantation could enhance heat tolerance of the sensitive wild-type C. proliferum, we transplanted bacterial communities from heat-evolved to the wild-type strain and subjected it to acute heat stress. Microbiome transplantation resulted in the incorporation of only 30 low-abundance strains into the microbiome of wild-type cultures, while the relative abundance of 14 pre-existing strains doubled in inoculated versus uninoculated samples. Inoculation with either wild-type or heat-evolved bacterial communities boosted C. proliferum growth, although no difference in heat tolerance was observed between the two inoculation treatments. This study provides evidence that Symbiodiniaceae-associated bacterial communities respond to heat selection and may contribute to coral adaptation to climate change.

Description of Flavimaribacter sediminis gen. nov., sp. nov., a New Member of the Family Rhizobiaceae Isolated from Marine Sediment

A novel Gram-staining-negative, aerobic and rod-shaped bacterium, designated WL0058T, was isolated from coastal sediment sample collected in Nantong city, Jiangsu province of China (120° 51' 13″ E, 32° 6' 26″ N) in October 2020. Strain WL0058T was found to grow at 4-37 °C (optimum, 28 °C) with 1.5-4.0% NaCl (optimum, 4.0%) and displayed alkaliphilic growth with the pH range of pH 6.0-10.0 (optimum, pH 6.0). Phylogenetic trees constructed based on 16S rRNA gene sequence indicated that strain WL0058T is a member of the family Rhizobiaceae, shared the highest similarity with "Hoeflea prorocentri" CCTCC AB 2016294T (97.7%) and constituted a sub-cluster within the family with it, while the similarity with others in the family Rhizobiaceae was lower than 97.0%. The G + C content of genomic DNA was 59.5 mol%. Polar lipids profile of strain WL0058T included phosphatidylcholine (PC), phosphatidylethanolamine (PE), and glycolipid (GL), phosphatidylmonomethylethanolamine (PME) and two unidentified polar lipids (L). The major isoprenoid quinone was determined to be Q-10 and the major fatty acids were C16:0, C18:0, summed features 4 (iso-C17:1 and/or anteiso-C17:1), and summed features 8 (C18:1ω6c and/or C18:1ω7c). As inferred from the morphology, physiology, and biochemical analysis, genotypic characteristics, and the phylogenetic trees, strain WL0058T ought to be recognized as a novel genus in the family Rhizobiaceae, for which the name Flavimaribacter sediminis gen. nov., sp. nov. The type strain of Flavimaribacter sediminis gen. nov., sp. nov. is WL0058T (= MCCC 1K06063T = JCM 34659T = GDMCC 1.2448T).

Antimicrobial Activity Against Phytopathogens and Inhibitory Activity on Solanine in Potatoes of the Endophytic Bacteria Isolated From Potato Tubers

As an important global crop, the potato (Solanum tuberosum L.) contains the endotoxin solanine that leads to human poisoning and major economic losses. Poisoning symptoms and even acute poisoning may occur when the content of solanine in potatoes exceeds 200 mg/kg. In addition, potatoes are susceptible to some pathogenic bacteria, including Streptomyces scabies and Erwinia carotovora subsp. atroseptica (Van Hall) dye, which can cause potato scab and potato blackleg disease, respectively. In this study, 37 culturable endophytic bacteria strains were obtained from potato tubers based on the culture-dependent method. Results indicated that nine strains showed antimicrobial activity against at least one pathogen by antimicrobial activity screening and 23 strains showed inhibitory activity on solanine in potato tubers. Among them, strain P-NA2-14 (Bacillus megaterium NBRC 15308T, 99.31%) showed not only better antimicrobial activity against both the two indicator pathogens, but also the best inhibitory activity on solanine, which was proved to be a potential biocontrol bacterium. Meanwhile, the relationship between the distribution of the endophytic bacterial community and the content of solanine in potato tubers was studied by Illumina-based analysis, indicating that the distribution of the endophytic bacterial community was obviously influenced by the content of solanine. The results showed a new insight into the relationship between plant secondary metabolites and endophytic bacteria in potato tubers and provided potential new technical support for the biological control of potato storage.

Salaquimonas pukyongi gen. nov., sp. nov., a novel bacterium within the family Phyllobacteriaceae

A novel aerobic, Gram-negative bacterial strain, RR3-28^T, was isolated from a seawater recirculating aquaculture system in Busan, Republic of Korea. Cells were rod-shaped, non-motile, oxidase-positive, catalase-negative and grew optimally at 25-30 °C, pH 8.5 and 3 % (w/v) NaCl. Based on the results of phylogenetic analysis, strain RR3-28^T was most closely related to Zhengella mangrovi X9-2-2^T within the family Phyllobacteriaceae with 95.97 % 16S rRNA gene sequence similarity. The major cellular fatty acids were summed feature 8 (C_18 : 1ω7c and/or C_18 : 1ω6c, 71.1 %) and 11-methyl C_18 : 1ω7c (14.4 %). The major polar lipids were phosphatidylglycerol, phosphatidylethanolamine, phosphatidylmonomethylethanolamine, phosphatidylcholine and unidentified aminolipids. The predominant quinone was ubiquinone Q-10 and the DNA G+C content was 58.6 mol%. On the basis of its phenotypic and genotypic characteristics, strain RR3-28^T represents a novel genus and species belonging to the family Phyllobacteriaceae, for which the name Salaquimonas pukyongi gen. nov., sp. nov. is proposed. The type strain of the species is RR3-28^T (=KCTC 52649^T=DSM 107947^T).

Rhodophyticola porphyridii gen. nov., sp. nov., isolated from a red alga, Porphyridium marinum

A Gram-stain-negative, strictly aerobic and moderately halophilic bacterium, designated strain MA-7-27^T, was isolated from a marine red alga, Porphyridium marinum, in the Republic of Korea. The cells of strain MA-7-27^T were non-motile rods showing oxidase- and catalase-positive activities. Growth of strain MA-7-27^T was observed at 15-45 °C (optimum, 30 °C), pH 5.0-9.0 (pH 7.0) and in the presence of 0.0-5.0 % (w/v) NaCl (2.0 %). Strain MA-7-27^T contained C10 : 0, summed feature 1 (comprising iso-C15 : 1 h and/or C13 : 1 3-OH) and summed feature 8 (comprising C18 : 1 ω7c and/or C18 : 1 ω6c) as the major fatty acids. The only isoprenoid quinone detected was ubiquinone-10. The major polar lipids of strain MA-7-27^T were phosphatidylglycerol, two unidentified phospholipids and two unidentified aminolipids. The G+C content of the genomic DNA was approximately 63.6 mol%. Strain MA-7-27^T was most closely related to the type strains of Boseongicola aestuarii BS-W15^T and Nioella nitratireducens SSW136^T with 96.98 % and 96.12 % 16S rRNA gene sequence similarities, respectively, but phylogenetic analyses showed that strain MA-7-27^T formed a clearly distinct phylogenic lineage from the closely related strains. The phenotypic, chemotaxonomic and molecular properties support that strain MA-7-27^T represents a novel genus of the family Rhodobacteraceae, for which the name Rhodophyticola porphyridii gen. nov., sp. nov. is proposed. The type strain is MA-7-27^T (=KACC 18805^T=JCM 31537^T).

Zhengella mangrovi gen. nov., sp. nov., a novel member of family Phyllobacteriaceae isolated from mangrove sediment

A Gram-negative strain, designed X9-2-2^T, was isolated from mangrove sediment in Yunxiao Mangrove National Nature Reserve, China. Strain X9-2-2^T showed less than 96.2 % 16S rRNA gene sequence similarity to type strains of species with validly published names. Phylogenetic analysis based on 16S rRNA gene sequences and rpoB protein sequences revealed that strain X9-2-2^T formed a distinct monophyletic clade within the family Phyllobacteriaceae and clustered distantly with the genera Aliihoeflea, Phyllobacterium and Hoeflea. Cells of X9-2-2^T were rod-shaped, motile with subpolar or lateral flagella and facultative anaerobic. Optimal growth occurred at 30-37 °C, at pH 7 and in the presence of 2 % NaCl. The DNA G+C content of strain X9-2-2^T was 64.9 mol%. The major fatty acids were summed feature 8 (comprising C18 : 1ω7c and/or C18 : 1ω6c 56.0 %), iso -C17 : 0 (9.1 %) and C12 : 0 (6.6 %). The predominant respiratory quinone was ubiquinone-10 and the major polar lipids were diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylmonomethylethanolamine, an unidentified aminolipid and two unidentified polar lipids. According to its morphology, physiology, fatty acid composition and 16S rRNA gene signature nucleotide patterns, strain X9-2-2^T represents a novel species of a novel genus in the family Phyllobacteriaceae, for which the name Zhengella mangrovi gen. nov., sp. nov. is proposed. The type strain is X9-2-2^T (=MCCC 1K03307^T=JCM 32107^T).