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Two strains of bacteria designated strains S-53T and A27T were isolated from forest soil and subjected to polyphasic characterization. Cells were aerobic, Gram-staining-negative, catalase- and oxidase- positive, non-motile, non-spore-forming, rod-shaped, and yellow-pigmented. Flexirubin-type pigments were present. Both strains were positive for PNPG, hydrolysed casein, and tyrosine. A phylogenetic analysis based on its 16S rRNA gene sequence revealed that strains S-53T and A27T formed a lineage within the family Cytophagaceae that were distinct from various members of the genus Dyadobacter (98.9–93.2% sequence similarity). Closest member for strain S-53T was Dyadobacter jejuensis AM1R11T (95.7%) and for A27TDyadobacter endophyticus 65T (98.9%). The predominant respiratory quinone was MK-7 for both strains. The major polar lipid for both strains was phosphatidylethanolamine. The major cellular fatty acids for both strains were summed feature 3 (C16:1ω7c and/or C16:1ω6c), iso-C15:0, C16:1ω5c, and C16:0. The DNA G+C content of strains ranges from 46.5 to 48.7 mol%. On the basis of phenotypic, genotypic, chemotaxonomic, and phylogenetic analysis, both strains S-53T and A27T represent a novel member in the genus Dyadobacter, for which the name Dyadobacter flavus sp. nov. and Dyadobacter terricola sp. nov. are proposed, respectively. The type strain of D. flavus is S-53T (= KEMB 9005-541T = KACC 19149T = NBRC 112681T) and type strain of D. terricola is A27T (= KEMB 9005-524T = KACC 19147T = NBRC 112680T).

Glucuronoyl esterases (GEs) are serine-type hydrolase enzymes belonging to carbohydrate esterase family 15 (CE15), and they play a central role in the reduction of recalcitrance in plant cell walls by cleaving ester linkages between glucuronoxylan and lignin in lignocellulose. Recent studies have suggested that bacterial CE15 enzymes are more heterogeneous in terms of sequence, structure, and substrate preferences than their fungal counterparts. However, the sequence space of bacterial GEs has still not been fully explored, and further studies on diverse enzymes could provide novel insights into new catalysts of biotechnological interest. To expand our knowledge on this family of enzymes, we investigated three unique CE15 members encoded by Dyadobacter fermentans NS114 T , a Gram-negative bacterium found endophytically in maize/corn ( Zea mays ). The enzymes are dissimilar, sharing ≤ 39% sequence identity to each other‚ and were considerably different in their activities towards synthetic substrates. Combined analysis of their primary sequences and structural predictions aided in establishing hypotheses regarding specificity determinants within CE15, and these were tested using enzyme variants attempting to shift the activity profiles. Together, the results expand our existing knowledge of CE15, shed light into the molecular determinants defining specificity, and support the recent thesis that diverse GEs encoded by a single microorganism may have evolved to fulfil different physiological functions. Key points • D. fermentans encodes three CE15 enzymes with diverse sequences and specificities • The Region 2 inserts in bacterial GEs may directly influence enzyme activity • Rational amino acid substitutions improved the poor activity of the DfCE15A enzyme

Aims Plant growth-promoting rhizobacteria (PGPR) substantially improve plant growth and health, but their effects on the succession of rhizosphere microbiota throughout the growth period triggered by pre-inoculation have not yet been considered. Methods Pepper seedlings cultured from a bio-nursery substrate containing Bacillus velezensis NJAU-Z9 and ordinary nursery substrate were used in this study to evaluate the effects of pre-colonization of a PGPR strain at the seedling stage on yield enhancement. To elucidate the underlying mechanisms involved in the rhizosphere microbiota succession during the whole growth period and their association with yield enhancement, high-throughput sequencing combined with qPCR was conducted. Results The results showed that, compared to the control without inoculation, pre-inoculation led to a steady yield enhancement in two-season field trials, as well as higher rhizosphere bacterial richness (Chao1) and diversity (Shannon-Wiener). The plant growth stage as the first driving factor, followed by pre-colonization drove the variations of the rhizosphere microbial community composition according to multivariate regression tree analysis and principal coordinate analysis. Variance partitioning analysis (VPA) and Mantel test results showed that the previous plant growth period induced variations in the fungal and bacterial communities at the next stage. Compared to the seedling and flowering stages, the mature-stage microbial community showed a higher degree of explanation of yield enhancement. Additionally, pre-inoculation led to distinctive rhizosphere microbiota succession compared to the control, due to alteration of the initial community. The heat map analysis showed that the rhizosphere microbiota was related to crop yield. In addition to Bacillus velezensis NJAU-Z9, which showed stable abundance in the pepper rhizosphere, stable higher relative abundance of the bacterial genera Sphingomonas , Sphingopyxis , Bradyrhizobium , Chitinophaga , Dyadobacter , Streptomyces , Lysobacter , Pseudomonas and Rhizomicrobium , and the fungal genera Cladorrhinum , Cladosporium and Aspergillus throughout the growth period induced by pre-colonization was associated with yield enhancement. Conclusions Overall, we conclude that pre-colonization with PGPR changed the initial rhizosphere microbiota and that the plant was triggered to further select distinctive microbes to form unique rhizosphere microbial consortia at the later growth stages, which resulted in plant growth promotion.

A novel Gram-negative, aerobic, rod-shaped bacterium, RS19T, was isolated from rose rhizosphere soil. The strain was psychrophilic and showed good growth over a temperature range of 1–37 ℃. Colonies on TSB agar were circular, smooth, mucoid, convex with clear edges and yellow. Phylogenetic analysis based on 16S rRNA gene sequences characterized RS19T in the genus Dyadobacter and showed that strain RS19T was most closely related to Dyadobacter psychrophilus CGMCC 1.8951T (97.4%) and Dyadobacter alkalitolerans CGMCC 1.8973T (97.1%). The average nucleotide identity values to the closest related species type strains were less than 84.0%. The DNA G + C content was 43.1 mol%, and the predominant respiratory menaquinone was MK-7. The major fatty acids were summed features 3 (C16:1ω7c and/or C16:1ω6c), iso-C15:0, C16:1ω5c and iso-C17:0 3-OH. Based on genotypic, phenotypic and chemotaxonomic data, strain RS19T is different from closely related species of the genus Dyadobacter. RS19T represents a novel species within the genus Dyadobacter, for which the name Dyadobacter luteus sp. nov. is proposed. The type strain is RS19T (= CGMCC 1.13719T = ACCC 60381T = JCM 32940T).

Heavy-metal (HM) contamination is a huge environmental problem in many countries including Mexico. Currently, microorganisms with multiple heavy-metal resistance and/or plant-promoting characteristics have been widely used for bioremediation of HM-contaminated soils. The aim of the study was isolated bacteria with multiple heavy-metal resistance and to determinate the resistance mechanism developed by these organisms. A total of 138 aerobic bacteria were isolated from soil and sediments surrounding the Lerma–Chapala basin located in the boundary of the States of Michoacán and Jalisco states of Mexico. One hundred and eight strains showed at least 1 plant growth-promoting features. The Lerma–Chapala basin bacteria were also resistant to high concentrations of HMs including the metalloid arsenic. Sequence analysis of 16S RNA genes reveled that these bacteria were mainly affiliated to the phyla Proteobacteria (38%), Firmicutes (31%) and Actinobacteria (25%), covering 21 genera with Bacillus as the most abundant one. Among them, at least 27 putative novel species were detected in the genera Acinetobacter, Arthrobacter, Bacillus, Agrobacterium, Dyadobacter, Enterobacter, Exiguobacterium, Kluyvera, Micrococcus, Microbacterium and Psychrobacter. In addition, these bacteria developed various heavy-metal-resistance mechanisms, such as biosorption/bioaccumulation, immobilization and detoxification. Therefore, the bacteria isolated from soils and sediments of Lerma–Chapala basin could be used in bioremediation strategies.

Carbohydrate epimerases and isomerases are essential for the metabolism and synthesis of carbohydrates. In this study, Runella slithyformis Runsl_4512 and Dyadobacter fermentans Dfer_5652 were characterized from a cluster of uncharacterized proteins of the acylglucosamine 2-epimerase (AGE) superfamily. These proteins catalyzed the intramolecular conversion of d -mannose to d -glucose, whereas they did not act on β-(1 → 4)-mannobiose, N -acetyl- d -glucosamine, and d -fructose, which are substrates of known AGE superfamily members. The k cat / K m values of Runsl_4512 and Dfer_5652 for d -mannose epimerization were 3.89 and 3.51 min −1  mM −1 , respectively. Monitoring the Runsl_4512 reaction through 1 H-NMR showed the formation of β- d -glucose and β- d -mannose from d -mannose and d -glucose, respectively. In the reaction with β- d -glucose, β- d -mannose was produced at the initial stage of the reaction, but not in the reaction with α- d -glucose. These results indicate that Runsl_4512 catalyzed the 2-epimerization of the β-anomer substrate with a net retention of the anomeric configuration. Since 2 H was obviously detected at the 2-C position of d -mannose and d -glucose in the equilibrated reaction mixture produced by Runsl_4512 in 2 H 2 O, this enzyme abstracts 2-H from the substrate and adds another proton to the intermediate. This mechanism is in accordance with the mechanism proposed for the reactions of other epimerases of the AGE superfamily, that is, AGE and cellobiose 2-epimerase. Upon reaction with 500 g/L d -glucose at 50 °C and pH 8.0, Runsl_4512 and Dfer_5652 produced d -mannose with a 24.4 and 22.8% yield, respectively. These d -mannose yields are higher than those of other enzyme systems, and ME acts as an efficient biocatalyst for producing d -mannose.

A Gram-negative, aerobic, nonmotile, rod-shaped and yellow-pigment-producing bacteria was isolated from Baima snow mountain of Diqing Tibetan Autonomous Prefecture in Yunnan province, south-west China and characterized using a polyphasic approach. The results of 16S rRNA gene sequence similarity analysis showed that strain YIM B04101T was closely related to the type strain of Dyadobacter koreensis DSM 19938T (97.81%) and Dyadobacter frigoris AR-3-8T (97.95%). The predominant respiratory quinone was menaquinone-7 (MK-7). The major polar lipid was phosphatidylethanolamine. The major fatty acids were summed feature 3 (C16:1ω7c/C16:1ω6c), C18:1ω9c and C16:0. The DNA G + C content was 43.5 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the strain YIM B04101T belonged to a cluster comprising species of the genus Dyadobacter. However, it differed from its closest relative, Dyadobacter koreensis KCTC 12537T and Dyadobacter frigoris AR-3-8T, in many physiological properties. Based on these phenotypic characteristics and phylogenetic distinctiveness, strain YIM B04101T is considered to be a novel species of the genus Dyadobacter, for which the name Dyadobacter diqingensis sp. nov. is proposed. The type strain is YIM B04101T (= CGMCC 1.19249T = CCTCC AB 2021270).

In this study, we examined the bacterial endophyte community of potato (Solanum tuberosum) cultivar/clones using two different molecular-based techniques (bacterial automated ribosomal intergenic spacer analysis (B-ARISA) and pyrosequencing). B-ARISA profiles revealed a significant difference in the endophytic community between cultivars (perMANOVA, p < 0.001), and canonical correspondence analysis showed a significant correlation between the community structure and plant biomass (p = 0.001). Pyrosequencing detected, on average, 477 ± 71 bacterial operational taxonomic units (OTUs, 97% genetic similarity) residing within the roots of each cultivar, with a Chao estimated total OTU richness of 1,265 ± 313. Across all cultivars, a total of 238 known genera from 15 phyla were identified. Interestingly, five of the ten most common genera (Rheinheimera, Dyadobacter, Devosia, Pedobacter, and Pseudoxanthomonas) have not, to our knowledge, been previously reported as endophytes of potato. Like the B-ARISA analysis, the endophytic communities differed between cultivar/clones (∫-libshuff, p < 0.001) and exhibited low similarities on both a presence/absence (0.145 ± 0.019) and abundance (0.420 ± 0.081) basis. Seventeen OTUs showed a strong positive (r > 0.600) or negative (r < −0.600) correlation with plant biomass, suggesting a possible link between plant production and endophyte abundance. This study represents one of the most comprehensive assessments of the bacterial endophytic communities to date, and similar analyses in other plant species, cultivars, or tissues could be utilized to further elucidate the potential contribution(s) of endophytic communities to plant physiology and production.

Vermicomposting is a promising method for corn stover management to achieve bioresource recovery and environmental protection. Most β-glucosidases, which limit the cellulose degradation rate during vermicomposting of corn stover, belong to glycoside hydrolase family 1 (GH 1 ). This study was conducted with different earthworm densities to quantify the GH 1 gene abundance and investigate the evolution of GH 1 cellulase-producing microbial communities using qPCR and pyrosequencing. The results showed that β-glucosidase activity, GH 1 gene abundance, TOC, and microbial communities carrying the GH 1 gene were affected by processing time and earthworm density. After introducing earthworms, β-glucosidase activity increased to 1.90–2.13 U/g from 0.54 U/g. The GH 1 gene abundance of treatments with earthworms (5.82E+09–6.70E+09 copies/g) was significantly higher than that of treatments without earthworms (2.48E+09 copies/g) on Day 45. Earthworms increased the richness of microbial communities. The relative abundances of Sphingobium and Dyadobacter , which are dominant genera harboring the GH 1 gene, were increased by earthworms to peak values of 23.90% and 11.20%, respectively. Correlation analysis showed that Sphingobium , Dyadobacter , Trichoderma , and Starkeya were positively associated with β-glucosidases. This work sheds new light on the mechanism of cellulose degradation during vermicomposting at the molecular level.

The aim of this study was isolation and characterization of heterotrophic bacteria capable of ammonium and nitrite removal at 15 °C (optimal temperature for growing rainbow trout Oncorhynchus mykiss). Environmental isolates were grown in liquid media containing ammonium or nitrite, and best strains in terms of growth and ammonium or nitrite removal were identified via 16S rRNA sequencing. Dyadobacter sp. (no. 68) and Janthinobacterium sp. (no. 100) were selected for optimal adaptation to growth at 15 °C and best ammonium and nitrite removal (P < 0.05), respectively. A heterotrophic ammonium and nitrite removal (HAN) microbial complex, containing selected strains, was prepared and applied in a trout culture system. After 10 days, the effect of microbial HAN complex was investigated in terms of ammonium and nitrite removal, as well as stress and immune indices present in the plasma of cultivated trout. Compared to a standard cultivation setup, addition of the HAN complex had a clear beneficial effect on keeping the un-ionized ammonia and nitrite level below prescribed standards (P < 0.05). This resulted in reduction of stress and immune reactions of cultivated fish (P < 0.05), leading to an augmentation of final weight and survival. Application of the selected microbial complex resulted in a significant improvement of the aquaculture ecosystem.