Pan-Genome Analyses of the Genus Cohnella and Proposal of the Novel Species Cohnella silvisoli sp. nov., Isolated from Forest Soil

Two strains, designated NL03-T5T and NL03-T5-1, were isolated from a soil sample collected from the Nanling National Forests, Guangdong Province, PR China. The two strains were Gram-stain-positive, aerobic, rod-shaped and had lophotrichous flagellation. Strain NL03-T5T could secrete extracellular mucus whereas NL03-T5-1 could not. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the two strains belong to the genus Cohnella, were most closely related to Cohnella lupini LMG 27416T (95.9% and 96.1% similarities), and both showed 94.0% similarity with Cohnella arctica NRRL B-59459T, respectively. The two strains showed 99.8% 16S rRNA gene sequence similarity between them. The draft genome size of strain NL03-T5T was 7.44 Mbp with a DNA G+C content of 49.2 mol%. The average nucleotide identities (ANI) and the digital DNA-DNA hybridization (dDDH) values between NL03-T5T and NL03-T5-1 were 99.98% and 100%, indicating the two strains were of the same species. Additionally, the ANI and dDDH values between NL03-T5T and C. lupini LMG 27416T were 76.1% and 20.4%, respectively. The major cellular fatty acids of strain NL03-T5T included anteiso-C15:0 and iso-C16:0. The major polar lipids and predominant respiratory quinone were diphosphatidylglycerol (DPG) and menaquinone-7 (MK-7). Based on phylogenetic analysis, phenotypic and chemotaxonomic characterization, genomic DNA G+C content, and ANI and dDDH values, strains NL03-T5T and NL03-T5-1 represent novel species in the genus Cohnella, for which the name Cohnella silvisoli is proposed. The type strain is NL03-T5T (=GDMCC 1.2294T = JCM 34999T). Furthermore, comparative genomics revealed that the genus Cohnella had an open pan-genome. The pan-genome of 29 Cohnella strains contained 41,356 gene families, and the number of strain-specific genes ranged from 6 to 1649. The results may explain the good adaptability of the Cohnella strains to different habitats at the genetic level.

Microbial diversity alteration reveals biomarkers of contamination in soil-river-lake continuum

Microbial communities inhabiting soil-water-sediment continuum in coastal areas provide important ecosystem services. Their adaptation in response to environmental stressors, particularly mitigating the impact of pollutants discharged from human activities, has been considered for the development of microbial biomonitoring tools, but their use is still in the infancy. Here, chemical and molecular (16S rRNA gene metabarcoding) approaches were combined in order to determine the impact of pollutants on microbial assemblages inhabiting the aquatic network of a soil-water-sediment continuum around the Ichkeul Lake (Tunisia), an area highly impacted by human activities. Samples were collected within the soil-river-lake continuum at three stations in dry (summer) and wet (winter) seasons. The contaminant pressure index (PI), which integrates Polycyclic aromatic hydrocarbons (PAHs), alkanes, Organochlorine pesticides (OCPs) and metal contents, and the microbial pressure index microgAMBI, based on bacterial community structure, showed significant correlation with contamination level and differences between seasons. The comparison of prokaryotic communities further revealed specific assemblages for soil, river and lake sediments. Correlation analyses identified potential "specialist" genera for the different compartments, whose abundances were correlated with the pollutant type found. Additionally, PICRUSt analysis revealed the metabolic potential for pollutant transformation or degradation of the identified "specialist" species, providing information to estimate the recovery capacity of the ecosystem. Such findings offer the possibility to define a relevant set of microbial indicators for assessing the effects of human activities on aquatic ecosystems. Microbial indicators, including the detection of "specialist" and sensitive taxa, and their functional capacity, might be useful, in combination with integrative microbial indices, to constitute accurate biomonitoring tools for the management and restoration of complex coastal aquatic systems.

Culture-dependent and -independent methods revealed an abundant myxobacterial community shaped by other bacteria and pH in Dinghushan acidic soils

Myxobacteria are one of the most promising secondary metabolites producers. However, they are difficult to isolate and cultivate. To obtain more myxobacteria and know the effects of environmental factors on myxobacterial community, we characterized myxobacterial communities in Dinghushan acidic forest soils of pH 3.6-4.5 with culture-dependent and -independent techniques, and analyzed environmental factors shaping myxobacterial communities. A total of 21 myxobacteria were isolated using standard cultivation methods, including eleven isolates of Corallococcus, nine isolates of Myxococcus and one isolate of Archangium, and contained three potential novel species. In addition, a total of 67 unknown myxobacterial operational taxonomic units (OTUs) were obtained using high-throughput sequencing method. The abundance of Myxococcales account for 0.9-2.2% of bacterial communities, and Sorangium is the most abundant genus (60.1%) in Myxococcales. Correlation analysis demonstrated that bacterial diversity and soil pH are the key factors shaping myxobacterial community. These results revealed an abundant myxobacterial community which is shaped by other bacteria and pH in Dinghushan acidic forest soils.

Rhizobium glycinendophyticum sp. nov., isolated from roots of Glycine max (Linn. Merr.)

A Gram-stain-negative, rod-shaped and aerobic bacterium, designated CL12T, was isolated from roots of Glycine max (Linn. Merr.) collected from an experimental field in the campus of South China Agricultural University, PR China (22°58'46″S, 110°51'10″E). Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain CL12T belongs to the genus Rhizobium, closely related to Rhizobium wuzhouense W44T (99.3%), followed by Rhizobium rosettiformans W3T (98.0%) and Rhizobium ipomoeae Shin9-1T (97.9%). The results of analysis of sequences of four housekeeping genes (recA, atpD, rpoB and glnA) also revealed strain CL12T to be closely related to R. wuzhouense W44T with the similarities 91.0%, 95.0%, 94.2% and 90.5%, respectively. The major fatty acid of strain CL12T was Summed Feature 8 (C18:1ω7c and/or C18:1ω6c). Strain CL12T had not the nodulation genes (nodC and nodA) and nitrogenase reductase gene (nifH), and could not cause formation of nodule on soybean. The draft genome size of strain CL12T was 4.84 Mbp with a genomic DNA G + C content of 61.1 mol%. The digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) of strain CL12T and R. wuzhouense W44T were 27.4% and 84.7%, respectively. Based on genomic, phenotypic and phylogenetic analysis, strain CL12T is suggested to represent a new species of the genus Rhizobium, for which the name Rhizobium glycinendophyticum sp. nov. is proposed. The type strain is CL12T (=GDMCC 1.1597T = KACC 21281T).

Deminuibacter soli gen. nov., sp. nov., isolated from forest soil, and reclassification of Filimonas aurantiibacter as Arvibacter aurantiibacter comb. nov

A novel strain, designated K23C18032701^T, was isolated from a sample of forest soil collected from Dinghushan Biosphere Reserve, Guangdong Province, PR China. The strain was Gram-stain-negative, aerobic, motile and showed a shape change from a filamentous cell to coccobacilli. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the novel strain belongs to the family Chitinophagaceae, and showed the highest similarities to Arvibacter flaviflagrans JCM 31293^T (95.0 %) and Filimonas aurantiibacter LMG 29039^T (94.4 %). The major cellular fatty acids included iso-C15 : 0, iso-C17 : 0 3-OH and iso-C15 : 1 G. The predominant polar lipid was phosphatidylethanolamine (PE). The predominant respiratory quinone was menaquinone-7. The major polyamine was sym-homospermidine. The draft genome size of strain K23C18032701^T was 5.84 Mb with a DNA G+C content of 47.2 mol%. Based on phenotypic, genotypic and phylogenetic analysis, strain K23C18032701^T represents a novel species of a new genus in the family Chitinophagaceae, for which the name Deminuibacter soli is proposed. The type strain is K23C18032701^T (=GDMCC 1.1403^T=KCTC 62913^T). We also propose the reclassification of Filimonas aurantiibacter as Arvibacter aurantiibacter comb. nov. (type strain 1458^T=NRRL B-65305^T=LMG 29039^T).

Chitinophaga silvisoli sp. nov., isolated from forest soil

A Gram-stain-negative, rod-shaped and aerobic bacterium, designated K20C18050901^T, was isolated from forest soil collected on 11 September 2017 from Dinghushan Biosphere Reserve, Guangdong Province, PR China (23° 10' 24'' N; 112° 32' 10'' E). Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain K20C18050901^T belongs to the genus Chitinophaga, and showed the highest similarities to Chitinophaga sancti NBRC 15057^T (98.6 %) and Chitinophaga oryziterrae JCM 16595^T (96.9 %). The major fatty acids (>10 %) were iso-C15 : 0, C16 : 1ω5c, summed feature 3 (C16 : 1ω6c and/or C16 : 1ω7c) and iso-C17 : 0 3-OH. The predominant respiratory quinone was menaquinone-7. The major polar lipid was phosphatidylethanolamine. The draft genome size of strain K20C18050901^T was 8.36 Mb with a DNA G+C content of 44.7 mol%. The digital DNA-DNA hybridization and average nucleotide identity values between strain K20C18050901^T and C. sancti NBRC 15057^T were 31.40 and 85.82 %, respectively. On the basis of phenotypic, genotypic and phylogenetic analysis, strain K20C18050901^T represents a novel species of the genus Chitinophaga, for which the name Chitinophagasilvisoli sp. nov. is proposed. The type strain is K20C18050901^T (=GDMCC 1.1411^T=KCTC 62860^T).

Niveitalea solisilvae gen. nov., sp. nov., isolated from forest soil and emended description of the genus Flavihumibacter Zhang et al. 2010

A Gram-stain-negative and strictly aerobic bacterial strain, designated 6-4T, was isolated from forest soil in Jeju island, South Korea. Cells showing oxidase-positive and catalase-negative reactions were thin and long non-motile rods. Growth of strain 6-4T was observed at 20-35 °C (optimum, 30 °C) and pH 6.0-9.0 (optimum, pH 7.0). Strain 6-4T contained iso-C15 : 0, anteiso-C15 : 0, iso-C15 : 1 G and iso-C17 : 0 3-OH as the major fatty acids and menaquinone-7 (MK-7) as the sole isoprenoid quinone. Phosphatidylethanolamine was the major polar lipid and five unidentified aminolipids, one unidentified aminophospholipid and one unidentified lipid were also detected as minor polar lipids. The G+C content of the genomic DNA was 45.8 mol%. Strain 6-4T was most closely related to Flavihumibacter solisilvae 3-3T with a low 16S rRNA gene sequence similarity (94.2 %) and phylogenetic analysis indicated that the strain formed a distinct phylogenetic lineage from members of the genus Flavihumibacter and other closely related genera. On the basis of phylogenetic inference and phenotypic, chemotaxonomic and molecular properties, strain 6-4T represents a novel species of a new genus of the family Chitinophagaceae, for which the name Niveitalea solisilvae gen. nov., sp. nov. is proposed. The type strain of Niveitalea solisilvae is 6-4T (=KACC 18808T=JCM 31525T). An emended description of the genus Flavihumibacter is also proposed.