Three marine bacteria in Bacteroidales, designated FJH62T, FJH65T and FJH54T, were isolated from mangrove sediments at the Zhangjiang River estuary in Fujian, China. The cells were Gram-stain-negative, facultatively anaerobic, non-motile and straight to curved rod-shaped. Comparative analysis of the 16S rRNA gene showed that strains FJH62T and FJH65T shared 88.9-89.0 % identity with Saccharicrinis carchari SS12T, while strain FJH54T had the maximum similarity of 88.8 % to Carboxylicivirga taeanensis MEBiC 08093T. Whole-genome relatedness indices further distinguished these isolates from other relatives, falling below the established thresholds, with strains FJH62T, FJH65T, and FJH54T identified as three distinct novel species. Phylogenetic analysis based on both 16S rRNA gene and whole genome sequences indicated that these three novel strains form a monophyletic branch within the order Bacteroidales. These isolates were distinguished from their closest relatives by the presence of MK-10 as the major respiratory quinone and phosphatidylethanolamine, aminolipids, and phospholipids as the predominant polar lipids. The major cellular fatty acids and DNA G + C content were identified as iso-C15:0 and anteiso-C15:0 and 38.5-39.9 %, respectively. Genomic analysis and experimental validation confirmed nitrogen-fixing and Fe(III)-reducing abilities of these three strains. Based on polyphasic characterizations, these three strains represent three novel species of a novel genus, for which the names Quyinboa mangrovi gen. nov., sp. nov. (FJH62T = KCTC 102258T = MCCC 1H01534T), Quyinboa ferrireducens sp. nov. (FJH65T = KCTC 102259T = MCCC 1H01536T), and Quyinboa sediminis sp. nov. (FJH54T = KCTC 102257T = MCCC 1H01535T) are proposed. Furthermore, a novel family, Quyinboaceae fam. nov., is proposed within the order Bacteroidales.

ABSTRACT The widespread cellulolytic specialist Cytophaga hutchinsonii belonging to the phylum Bacteroidetes adopted a unique cellulose utilization strategy that did not conform to the known cellulose-degrading paradigms involving free cellulases or cellulosomes. The strategy used by C. hutchinsonii still remains largely unclear. In this study, we showed that chu_1279 within the chu_1276–chu_1280 gene cluster, which has been previously shown to be important for cellulose utilization by C. hutchinsonii , encodes an outer membrane protein, and its elimination prohibited bacterial growth on cellulose. Structural prediction revealed that CHU_1279 is a surface glycan-binding protein B (SGBP-B)-like protein comprising two putative carbohydrate-binding module (CBM)-like domains. Further analyses verified that recombinant CHU_1279 displayed significant cellulose-binding protein, and its C-terminal domain is predominantly responsible for cellulose binding. Expression of the C-terminal domain but not the N-terminal domain restored cellulose utilization of ∆ chu_1279 . Moreover, site-directed mutagenesis analyses identified three aromatic residues important for cellulose binding of the recombinant CHU_1279 protein. The defective cellulose utilization of ∆ chu_1279 cells otherwise could be recovered by CHU_1279 variants with significantly damaged cellulose-binding capability. Sequence analyses revealed that orthologs of CHU_1279 as well as the atypical polysaccharide utilization loci (PUL) constituted by the gene cluster chu_1276–chu_1280 are also present in two other cellulolytic Bacteroidetes bacteria, Cytophaga aurantiaca and Sporocytophaga myxococcoides , which are closely related to C. hutchinsonii . Our results contribute to unveiling the unique mechanism underlying the efficient cellulose utilization by C. hutchinsonii and similar cellulolytic bacteria. IMPORTANCE Most members of the phylum Bacteroidetes are highly competitive and efficient degraders of complex polysaccharides largely ascribed to their employment of a SusC-like system encoded by a polysaccharide utilization locus (PUL). However, characterization of PULs is limited to those responsible for utilization of (semi)soluble glycans. PULs involved in the utilization of cellulose, the most abundant renewable polymer, have not been identified and functionally characterized yet. We demonstrated that chu_1279 in the cellulolytic specialist C. hutchinsonii encodes an SGBP-B-like protein that is required for cellulose utilization, supporting that the gene cluster chu_1276–chu_1280 in C. hutchinsonii encodes an atypical PUL system dedicated to cellulose assimilation. Further analyses showed that this atypical PUL system is also present in two other cellulolytic Bacteroidetes bacteria. This study not only contributes to unveiling the unusual cellulose utilization strategy adopted by C. hutchinsonii and similar cellulolytic bacteria but also helps expand our understanding of atypical PULs for nutrient acquisition by cellulolytic bacteria.

In the classical microbial isolation technique, the isolation process inevitably destroys all microbial interactions and thus makes it difficult to culture the many microorganisms that rely on these interactions for survival. In this study, we designed a simple coculture technique named the "sandwich agar plate method," which maintains microbial interactions throughout the isolation and pure culture processes. The total yield of uncultured species in sandwich agar plates based on eight helper strains was almost 10-fold that of the control group. Many uncultured species displayed commensal lifestyles. Further study found that heme was the growth-promoting factor of some marine commensal bacteria. Subsequent genomic analysis revealed that heme auxotrophies were common in various biotopes and prevalent in many uncultured microbial taxa. Moreover, our study supported that the survival strategies of heme auxotrophy in different habitats varied considerably. These findings highlight that cocultivation based on the "sandwich agar plate method" could be developed and used to isolate more uncultured bacteria.

Brown algae are rich in biostimulants that not only stimulate the overall development and growth of plants but also have great beneficial effects on the whole soil-plant system. However, alginate, the major component of brown algae, is comparatively difficult to degrade. The cost of preparing alginate oligosaccharides (AOSs) is still too high to produce seaweed fertilizer. In this work, the marine bacterium Vibrio sp. B1Z05 is found to be capable of efficient alginate depolymerization and harbors an extended pathway for alginate metabolism. The B1Z05 extracellular cell-free supernatant exhibited great potential for AOS production at low cost, which, together with cellulase, can efficiently hydrolyze seaweed. The brown algal hydrolysis rates were significantly greater than those of the commercial alginate lyase product CE201, and the obtained seaweed extracts were rich in phytohormones. This work provides a low-cost but efficient strategy for the sustainable production of desirable AOSs and seaweed fertilizer.

Bradymonabacteria, as the representative of the facultative prey-dependent predators, were re-classified from the preceding Deltaproteobacteria into the phylum Myxococcota and proposed as a novel class named Bradymonadia. However, it was ambiguous whether their predatory pattern and properties were similar to those of the other myxobacterial predators. Therefore, the physiologic features were compared to determine the similarities and differences during the process of group attack and kin discrimination. Comparative genomic analyses were performed to conclude the core genome encoded commonly by bradymonabacteria, Myxococcia, and Polyangia. In conclusion, we proposed that bradymonabacteria have a predation pattern similar to the that of the representative of opportunistic predators like Myxococcus xanthus but with some subtle differences. Their predation was predicted to be initiated by the needle-less T3SS*, and the S-motility mediated by T4P also participated in the process. Meanwhile, their group attacks relied on cell contact and cell destiny. Inter-species (strains) kin discriminations occurred without the existence of T6SS. However, no extracellular lethal substance was detected in the fermentation liquor culture of bradymonabacteria, and the death of prey cells could only be observed when touched by their cells. Moreover, the prey-selective predation was observed when the predator encountered certain prey from Bacillus (G+), Algoriphagus (G−), and Nocardioides (G+). Bradymonabacteria can be regarded as a potential consumer and decomposer, and preying on many sea-dwelling or human pathogenic bacteria allows this group a broad application prospect in marine culture and clinical disease control. Our study will provide more evidence for its exploitations and applications.

Marine macroalgae are increasingly recognized for their significant biological and economic potential. The key to unlocking this potential lies in the efficient degradation of all carbohydrates from the macroalgae biomass. However, a variety of polysaccharides (alginate, cellulose, fucoidan, and laminarin), are difficult to degrade simultaneously in a short time. In this study, the brown alga Saccharina japonica was found to be rapidly and thoroughly degraded by the marine bacterium Agarivorans albus B2Z047. This strain harbors a broad spectrum of carbohydrate-active enzymes capable of degrading various polysaccharides, making it uniquely equipped to efficiently break down both fresh and dried kelp, achieving a hydrolysis rate of up to 52%. A transcriptomic analysis elucidated the presence of pivotal enzyme genes implicated in the degradation pathways of alginate, cellulose, fucoidan, and laminarin. This discovery highlights the bacterium’s capability for the efficient and comprehensive conversion of kelp biomass, indicating its significant potential in biotechnological applications for macroalgae resource utilization.

Many marine bacteria are difficult to culture because they are dormant, rare or found in low-abundances. Enrichment culturing has been widely tested as an important strategy to isolate rare or dormant microbes. However, many more mechanisms remain uncertain. Here, based on 16S rRNA gene high-throughput sequencing and metabolomics technology, it was found that the short-chain fatty acids (SCFAs) in metabolites were significantly correlated with uncultured bacterial groups during enrichment cultures. A pure culture analysis showed that the addition of SCFAs to media also resulted in high efficiency for the isolation of uncultured strains from marine sediments. As a result, 238 strains belonging to 10 phyla, 26 families and 82 species were successfully isolated. Some uncultured rare taxa within Chlorobi and Kiritimatiellaeota were successfully cultured. Amongst the newly isolated uncultured microbes, most genomes, e.g. bacteria, possess SCFA oxidative degradation genes, and these features might aid these microbes in better adapting to the culture media. A further resuscitation analysis of a viable but non-culturable (VBNC) Marinilabiliales strain verified that the addition of SCFAs could break the dormancy of Marinilabiliales in 5 days, and the growth curve test showed that the SCFAs could shorten the lag phase and increase the growth rate. Overall, this study provides new insights into SCFAs, which were first studied as resuscitation factors in uncultured marine bacteria. Thus, this study can help improve the utilisation and excavation of marine microbial resources, especially for the most-wanted or key players.

IntroductionMacroalgae contain various polysaccharides that serve as nutrient sources Introduction: Macroalgae contain various polysaccharides that serve as nutrient sources for marine bacteria. Carbohydrate-active enzymes (CAZymes) are the primary feature of marine bacteria that utilize these polysaccharides. In this study, we describe Tamlana sp. S12, a novel strain of marine flavobacteria that can degrade alginate and Laminaria japonica biomass, isolated from the intestines of the sea cucumber Apostichopus japonicas collected at Weihai coast.MethodsWe sequenced the entire genome of strain S12 and constructed a phylogenetic tree using the core genome sequences of related strains. We determined the enzymatic activity of strain S12 using the DNS method and measured its growth curve under different carbon sources using spectrophotometry.ResultsStrain S12 degraded dehydrated L. japonica fragments as the sole nutrient source within 48h. Strain S12 harbors a diverse array of CAZymes at multiple polysaccharide utilization loci (PUL). One PUL encoding lyases from PL6, 7, and 17 families may be used for the degradation of alginate. Additionally, strain S12 harbors PULs encoding carrageenan- and agar-targeting CAZymes. Comparative analysis with related flavobacteria from Algibacter, Maribacter, and Zobellia showed shared CAZymes among these strains, potentially derived from a common ancestor and stably maintained within strains. Genomic signatures, algal degradation ability, and CAZyme patterns suggest that strain S12 has the potential to degrade complex algal polysaccharides.ConclusionThese results expand our knowledge of CAZymes and enrich our understanding of how marine Flavobacteriaceae adapt to marine algal polysaccharide environments. The availability of the genome of Tamlana sp. S12 will be beneficial for further analyses of marine Flavobacteriaceae.

Magnetotactic bacteria (MTB) have the remarkable capability of producing intracellularly membrane-enveloped magnetic nanocrystals (i.e. magnetosomes) and swimming along geomagnetic field lines. Despite more than 50 years of research, bacterial diversity and magnetosome biomineralization within MTB are relatively less known in the Gammaproteobacteria class than other groups. This is incompatible with the status of Gammaproteobacteria as the most diverse class of gram-negative bacteria with a number of ecologically important bacteria. Here, we identify a novel MTB strain YYHR-1 affiliated with the Gammaproteobacteria class of the Pseudomonadota phylum from a freshwater lake. In YYHR-1, most magnetosome crystals are organized into a long chain aligned along the cell long axis; unusually, a few small superparamagnetic crystals are located at the side of the chain, off the main chain axis. Micromagnetic simulations indicate that magnetostatic interactions among adjacent crystals within a chain reduce the Gibbs energy to enhance chain stability. Genomic analysis suggests that duplication of magnetosome gene clusters may result in off-chain magnetosomes formation. By integrating available genomic data from Gammaproteobacteria, the phylogenetic position of MTB in this class is reassigned here. Our new findings expand knowledge about MTB diversity and magnetosome biomineralization, and deepen understanding of the phylogenetics of the Gammaproteobacteria.

Background The well-known industrial fungus Trichoderma reesei has an excellent capability of secreting a large amount of cellulases and xylanases. The induced expression of cellulase and xylanase genes is tightly controlled at the transcriptional level. However, compared to the intensive studies on the intricate regulatory mechanism of cellulase genes, efforts to understand how xylanase genes are regulated are relatively limited, which impedes the further improvement of xylanase production by T. reesei via rational strain engineering. Results To identify transcription factors involved in regulating xylanase gene expression in T. reesei , yeast one-hybrid screen was performed based on the promoters of two major extracellular xylanase genes xyn1 and xyn2 . A putative transcription factor named XTR1 showing significant binding capability to the xyn1 promoter but not that of xyn2 , was successfully isolated. Deletion of xtr1 significantly increased the transcriptional level of xyn1 , but only exerted a minor promoting effect on that of xyn2 . The xylanase activity was increased by ~ 50% with XTR1 elimination but the cellulase activity was hardly affected. Subcellular localization analysis of XTR1 fused to a green fluorescence protein demonstrated that XTR1 is a nuclear protein. Further analyses revealed the precise binding site of XTR1 and nucleotides critical for the binding within the xyn1 promoter. Moreover, competitive EMSAs indicated that XTR1 competes with the essential transactivator XYR1 for binding to the xyn1 promoter. Conclusions XTR1 represents a new transcriptional repressor specific for controlling xylanase gene expression. Isolation and functional characterization of this new factor not only contribute to further understanding the stringent regulatory network of xylanase genes, but also provide important clues for boosting xylanase biosynthesis in T. reesei .

Alzheimer’s disease (AD) is an age-related neurodegenerative disorder. Neuritic plaques containing amyloid-β protein (Aβ) and neurofibrillary tangles composed of hyperphosphorylated tau protein constitute major neuropathological hallmarks of AD. The neurotoxicity of aggregated Aβ has been implicated as a critical cause in the pathogenesis of AD. The aim of this study was to exam the use of neoagarohexaose (NAH) in the potential treatment of AD effects, using SH-SY5Y neuronal cell line exposed to β-amyloid protein (Aβ1-42). The present study was designed to explore the neuroprotective effects of NAH on neuroblastoma SH-SY5Y cells as a function of dosage. The cells were exposed to Aβ1-42 with or without NAH (26.7, 53.4, and 106.8 μM) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was used for detecting the viability of treated cells. In treated cells, the activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and malondialdehyde (MDA) were determined using their manufacturer kits. Flow cytometry analysis was used to assess apoptosis, changes in intracellular calcium concentration, and the mitochondrial membrane potential (MMP) after treatment. Additionally, changes in the mechanism of Aβ1-42 aggregation in the presence of NAH were explored using thioflavin T (ThT) and Congo red (CR) assays. The results showed that incubation with NAH prior to Aβ1-42 exposure increased cell survival and prevented reactive oxygen species generation. Moreover, NAH decreased the apoptotic rate, inhibited MMP depolarization, reversed the change in intracellular calcium concentration, enhanced the activities of SOD and GSH-Px, and decreased the level of MDA. In addition, the results showed that NAH, which reduced the absorption of the amyloid indicator ThT and CR dyes, was a potent inhibitor of Aβ fibrillogenesis. In conclusion, NAH protects SH-SH5Y cells from Aβ-induced damage by reducing oxidative stress and weakens the spontaneous amyloid formation of Aβ fibrils in vitro and can inhibit the amyloidization of amyloid β protein (Aβ). This study shows that NAH may be a promising anti-AD drug candidate for AD treatment.

Our model offers insight into the ecological properties of SRB and identifies a previously undocumented dimension of OM degradation. This targeted inhibition approach could provide a novel framework for illustrating how functional microbial taxa associate the composition and structure of the microbial community, molecular ecological network, and community assembly processes.

Salinity acts as a critical environmental filter on microbial communities in natural systems, negatively affecting microbial diversity. However, how salinity affects microbial community assembly remains unclear. This study used Wendeng multi-pond saltern as a model to evaluate the prokaryotic community composition and diversity and quantify the relative importance of ecological processes across salinity gradients. The results showed that low-saline salterns (45–80 g/L) exhibited higher bacterial diversity than high-saline salterns (175–265 g/L). The relative abundance of taxa assigned to Halomicrobiaceae, Rhodobacteraceae, Saprospiraceae, and Thiotrichaceae exhibited a hump-shaped dependence on increasing salinity. Salinity and pH were the primary environmental factors that directly or indirectly determined the composition and diversity of prokaryotic communities. Microbial co-occurrence network dynamics were more complex in the sediment than in the water of salterns. An infer Community Assembly Mechanisms by Phylogenetic-bin-based null model analysis (iCAMP) showed that microbial community assembly in sediment and water differed. Our findings provide more information about microbial community structure and the importance of various ecological processes in controlling microbial community diversity and succession along salinity gradients in water and sediment.

Branching sucrases, a subfamily of Glycoside Hydrolase family (GH70), display transglycosidase activity using sucrose as donor substrate to catalyze glucosylation reaction in the presence of suitable acceptor substrates. In this study, the (α1→3) branching sucrase GtfZ-CD2 from Apilactobacillus kunkeei DSM 12361 was demonstrated to glucosylate benzenediol compounds (i.e., catechol, resorcinol, and hydroquinone) to form monoglucoside and diglucoside products. The production and yield of catechol glucosylated products were significantly higher than that of resorcinol and hydroquinone, revealing a preference for adjacent aromatic hydroxyl groups in glucosylation. Amino residues around acceptor substrate binding subsite +1 were targeted for semirational mutagenesis, yielding GtfZ-CD2 variants with improved resorcinol and hydroquinone glucosylation. Mutant L1560Y with improved hydroquinone mono-glucosylated product synthesis allowed enzymatic conversion of hydroquinone into α-arbutin. This study thus revealed the high potential of GH70 branching sucrases for glucosylating noncarbohydrate molecules. IMPORTANCE Glycosylation represents one of the most important ways to expand the diversity of natural products and improve their physico-chemical properties. Aromatic polyphenol compounds widely found in plants are reported to exhibit various remarkable biological activities; however, they generally suffer from low solubility and stability, which can be improved by glycosylation. Our present study on the glucosylation of benzenediol compounds by GH70 branching sucrase GtfZ-CD2 and its semirational engineering to improve the glucosylation efficiency provides insight into the mechanism of acceptor substrates binding and its glucosylation selectivity. The results demonstrate the potential of using branching sucrase as an effective enzymatic glucosylation tool.

In this study, two bacterial strains designated F2608T and F1192T, isolated from marine sediment sampled in Weihai, PR China, were characterized using a polyphasic approach. Strains were aerobic, Gram-stain-negative and motile. According to the results of phylogenetic analyses based on their 16S rRNA genes, these two strains should be classified under the genus Psychrobacter and they both show <98.5% sequence similarity to their closest relative, Psychrobacter celer JCM 12601T. Moreover, strain F2608T showed 97.5% sequence similarity to strain F1192T. Strain F2608T grew at 4-37 °C (optimum, 30-33 °C) and at pH 6.0-9.0 (optimum, pH 6.5-7.0) in the presence of 0-12% (w/v) NaCl (optimum, 4.0-5.0%). Strain F1192T grew at 4-37 °C (optimum, 30 °C) and at pH 5.5-9.0 (optimum, pH 7.0-7.5) in the presence of 0.5-12% (w/v) NaCl (optimum, 3.0-4.0%). The genomic DNA G+C contents of strain F2608T and strain F1192T were 47.4 and 44.9 %, respectively. Genomic characteristics including average nucleotide identity and digital DNA-DNA hybridization values clearly separated strain F2608T from strain F1192T. The sole isoprenoid quinone in these two strains was ubiquinone 8 and the major cellular fatty acids (>10.0%) were C18:1 ω9c and C17:1 ω8c. The major polar lipids of these two strains were phosphatidylglycerol, phosphatidylethanolamine and diphosphatidylglycerol. Based on the results of polyphasic analysis, the two strains represent two novel species of the genus Psychrobacter, for which the names Psychrobacter halodurans sp. nov. and Psychrobacter coccoides sp. nov. are proposed. The type strains are F2608T (=MCCC 1K05774T=KCTC 82766T) and F1192T (=MCCC 1K05775T=KCTC 82765T), respectively.

A Gram-stain-negative, facultatively aerobic, pink and oval bacterium, designed OS4T, was isolated from a sediment sample taken from a coastal zone in China. The growth of OS4T occurred at 20–37 °C (optimal 25 °C), pH 7.0–8.5 (optimal pH 8.0), in 0–5.0% (w/v) NaCl (optimal 2.0%). According to the phylogenetic analysis, strain OS4T showed the highest sequence similarity (96.04%) with Jannaschia aquimarina GSW-M26T and shared 94.98% similarity with the type species of genus Jannaschia-strain J. helgolandensis 14858T. Chemotaxonomic analysis showed that the sole respiratory quinone was ubiquinone 10, and the major fatty acids (>5.0%) included C18:1 ω6c/ω7c, C18:0, and C10:0 3OH. The polar lipids consist of three phospholipids, two unknown amino-lipids, and four unknown glycerolipids. The DNA G + C content was 72.7 mol%. Based on the evidence presented in this study, strain OS4T represents a novel species of the genus Jannaschia, for which the name Jannaschia sedimins sp. nov. is proposed. The type strain is OS4T (=KCTC 82508T = MCCC 1K03755T). Both the phenotypic and the genetic analysis on the antimicrobial resistance genes indicate that OS4T is resistant to a wide range of classes of antibiotics, which highlights that the ocean could potentially serve as the natural reservoir of antimicrobial resistance genes.

Polymannuronic acid (PM) possesses more pharmacological activities than sodium alginate, but there have been few studies on its absorption mechanism, tissue distribution, and pharmacokinetics. Studies of pharmacokinetics and tissue distribution are necessary to elucidate the pharmacological effects of PM. Thus, we used fluorescein isothiocyanate (FITC) to produce fluorescently labeled PM (FITC-PM) and detected the distribution and pharmacokinetics of PM in vivo via tail vein injection. The results demonstrate that the FITC-PM showed high stability in different pH solutions. After the tail vein injection, FITC-PM tended to be distributed in the kidney, followed by the liver and in the heart, spleen, and lungs at lower concentrations. Pharmacokinetic analysis showed that the elimination rate constant of FITC-PM was 0.24, the half-life time was 2.85 h, the peak concentration was 235.17 μg/mL, the area under the curve was 631.48 μg/mL·h, the area under the curve by statistical moment was 1843.15 μg/mL·h2, the mean residence time was 2.92 h, and the clearance rate was 79.18 mL/h. These results indicate that FITC-PM could be used for PM distribution and pharmacokinetic studies, and the studies of pharmacokinetics and tissue distribution provided basic information that can be used to further clarify PM pharmacodynamic mechanisms.

Arabinan in plant cell wall constitutes a major source of arabinose and arabino-oligosaccharides in nature. Exo-alpha-L-1,5-arabinanases release arabinose or arabino-oligosaccharides from arabinan in an exo-acting manner and therefore contribute to arabinan degradation. In this study, an exo-alpha-L-1,5-arabinanase belonging to GH93 family was identified from the thermophilic filamentous fungus Rasamsonia emersonii. The corresponding encoding gene (Reabn93) was cloned from the R. emersonii genome and heterologously expressed in Pichia pastoris. The purified recombinant ReAbn93 exhibited the maximum activity at 70 degrees C and retained 70% of its activity after incubation at 70 degrees C for 3 h ReAbn93 had an acidic pH optimum (pH 4.0) but remained stable over a broad pH range (pH 3-9). The specific activity of ReAbn93 toward linear arabinan under optimal conditions was 466.08 U mg(-1). Similar to the few other reported GH93 members, ReAbn93 degrades linear arabinan or arabino-oligosaccharides in an exo-acting manner with arabinobiose as the only hydrolytic product. Of note, ReAbn93 possessed remarkably better thermostability and higher specific activity compared to the only reported thermophilic counterpart in GH93, and therefore holds potential in relevant biotechnological applications. (C) 2021, The Society for Biotechnology, Japan. All rights reserved.

A Gram-stain-negative, facultatively anaerobic, oxidase-negative and catalase-positive predatory bacillus, designated strain V1718T, was isolated from Xiaoshi Island, PR China. Strain V1718T was found to be closely related to Lujinxingia sediminis SEH01T, with 89.8 % similarity in the 16S rRNA gene sequence, followed by Bradymonas sediminis FA350T with a similarity of 88.4 %. Strain V1718T had the ability to prey on other bacteria, and selective predation on members of Algoriphagus, Nocardioides and Bacillus occurred with the strain. Growth was observed within the range of 20-45 °C (optimal at 37 °C), pH 6.5-9.0 (optimal at pH 8.0) and 1-10 % NaCl (optimal at 3-4 %, w/v). The predominant cellular fatty acids in strain V1718T were iso-C15 : 0 (53.0 %) and C16 : 0 (19.1 %). The major polar lipids present in the strain were phosphatidylglycerol and phosphatidylethanolamine, and the respiratory quinone was menaquinone MK-7. The complete genome sequence of strain V1718T was 5 847 748 bp with a G+C content of 55.2 mol%. The topology of the phylogenomic tree indicated that strain V1718T forms a separate branch in the same clade with the genus Lujinxingia and the family Bradymonadaceae. The average nucleotide identity and average amino acid identity values were 66.4 and 48.6 %, respectively, with Bradymonas sediminis FA350T (type species of Bradymonas) and 66.8 % and 48.9 % with Lujinxingia litoralis B210T (type species of Lujinxingia). The genes related to biosynthesis pathways of several important chemical compounds could not be found in the genome of strain V1718T, which was predicted to be the intrinsic reason for predation in this group. The physiological, biochemical and phylogenetic properties of strain V1718T suggest that it belongs to a novel family distinct from other culturable bradymonabacteria. The name Microvenator marinus gen. nov., sp. nov. is proposed, with strain V1718T (=KCTC 72082T=MCCC 1H00380T) as type strain; the name Microvenatoraceae fam. nov. is also proposed. Meanwhile, the genus Lujinxingia can also be taxonomic classified as Lujinxingiaceae fam. nov. Thus, two novel families and a novel genus of the order Bradymonadales are proposed in this paper.

Alginate is the main component of brown algae, which is an important primary production in marine ecosystems and represents a huge marine biomass. The efficient utilization of alginate depends on alginate lyases to catalyze the degradation, and remains to be further explored. In this study, 354 strains were isolated from the gut of adult abalones, which mainly feed on brown algae. Among them, 100 alginate-degrading strains were gained and the majority belonged to the Gammaproteobacteria, followed by the Bacteroidetes and Alphaproteobacteria. A marine bacterium, Agarivorans sp. B2Z047, had the strongest degradation ability of alginate with the largest degradation circle and the highest enzyme activity. The optimal alginate lyase production medium of strain B2Z047 was determined as 1.1% sodium alginate, 0.3% yeast extract, 1% NaCl, and 0.1% MgSO4 in artificial seawater (pH 7.0). Cells of strain B2Z047 were Gram-stain-negative, aerobic, motile by flagella, short rod-shaped, and approximately 0.7–0.9 µm width and 1.2–1.9 µm length. The optimal growth conditions were determined to be at 30 °C, pH 7.0–8.0, and in 3% (w/v) NaCl. A total of 12 potential alginate lyase genes were identified through whole genome sequencing and prediction, which belonged to polysaccharide lyase family 6, 7, 17, and 38 (PL6, PL7, PL17, and PL38, respectively). Furthermore, the degradation products of nine alginate lyases were detected, among which Aly38A was the first alginate lyase belonging to the PL38 family that has been found to degrade alginate. The combination of alginate lyases functioning in the alginate-degrading process was further demonstrated by the growth curve and alginate lyase production of strain B2Z047 cultivated with or without sodium alginate, as well as the content changes of total sugar and reducing sugar and the transcript levels of alginate lyase genes. A simplified model was proposed to explain the alginate utilization process of Agarivorans sp. B2Z047.