Fibrisoma montanum sp. nov., isolated from soil of Mountain Danxia, China.

A Gram-stain-negative, non-motile, rod-shaped, aerobic bacterium, designated HYT19T, was isolated from soil of Mountain Danxia in southern China. It showed the highest similarity of 16S rRNA gene sequence (97.0%) and formed a monophyletic clade with Fibrisoma limi BUZ 3T. Strain HYT19T grew at 16-37 °C (optimum 28-30 °C) and at pH 6-7. The draft genome size of strain HYT19T was 7.8 Mb with a DNA G+C content of 54.0 mol%. The digital DDH and average nucleotide identity values between strain HYT19T and F. limi BUZ 3T were 28.8% and 85.1%, respectively. MK-7 was the sole respiratory quinone. The major polar lipids were phosphatidylethanolamine, unidentified aminophospholipid, two unidentified aminolipids, unidentified phospholipid and unidentified lipid. The strain contained C16:1ω5c, iso-C15:0, summed feature 3 (C16:1ω6c and/or C16:1ω7c), C16:0, iso-C17:0 3-OH and anteiso-C15:0 as the major fatty acids. On the basis of phylogenetic, genomic, phenotypic and chemotaxonomic analysis, we propose a new species Fibrisoma montanum sp. nov. of genus Fibrisoma. The type strain is HYT19T (= CCTCC AB 2018342T = JCM 33105T).

Mucilaginibacter terrenus sp. nov., isolated from manganese mine soil.

Strain ZH6T is a Gram-stain-negative, rod-shaped, aerobic bacterium isolated from manganese mine soil. Strain ZH6T had highest 16S rRNA gene sequence similarities to Mucilaginibacter yixingensis YX-36T (96.9 %) and Mucilaginibacter psychrotolerans NH7-4T (96.8 %). The genome size of strain ZH6T was 4.61 Mb with a DNA G+C content of 44.0 mol%. The average nucleotide identity and digital DNA-DNA hybridization values between strain ZH6T and M. yixingensis DSM 26809T were 70.6 and 19.2 %, respectively. Strain ZH6T had menaquinone-7 as a major quinone and main cellular fatty acids of iso-C15 : 0, iso-C17 : 0 3-OH and summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c). The polar lipids of strain ZH6T were a phosphatidylethanolamine, an unidentified glycolipid, an unidentified phospholipid, three unidentified aminophospholipids and four unidentified lipids. Based on the phenotypic, chemotaxonomic and phylogenetic results, strain ZH6T represents a novel species of the genus Mucilaginibacter, for which the name Mucilaginibacterterrenus sp. nov., is proposed. The type strain is ZH6T (=CCTCC AB 2018373T=KCTC 72075T).

Novel mechanisms of selenate and selenite reduction in the obligate aerobic bacterium Comamonas testosteroni S44.

Selenium oxyanion reduction is an effective detoxification or/and assimilation processes in organisms, but little is known the mechanisms in aerobic bacteria. Aerobic Comamonas testosteroni S44 reduces Se(VI)/Se(IV) to less-toxic elemental selenium nanoparticles (SeNPs). For Se(VI) reduction, sulfate and Se(VI) reduction displayed a competitive relationship. When essential sulfate reducing genes were respectively disrupted, Se(VI) was not reduced to red-colored SeNPs. Consequently, Se(VI) reduction was catalyzed by enzymes of the sulfate reducing pathway. For Se(IV) reduction, one of the potential periplasm molybdenum oxidoreductase named SerT was screened and further used to analyze Se(IV) reduction. Compared to the wild type and the complemented mutant strain, the ability of Se(IV) reduction was reduced 75% in the deletion mutant ΔserT. Moreover, the Se(IV) reduction rate was significantly enhanced when the gene serT was overexpressed in Escherichia coli W3110. In addition, Se(IV) was reduced to SeNPs by the purified SerT with the presence of NADPH as the electron donor in vitro, showing a Vmax of 61 nmol/min·mg and a Km of 180 µmol/L. A model of Se(VI)/Se(IV) reduction was generated in aerobic C. testosteroni S44. This work provides new insights into the molecular mechanisms of Se(VI)/Se(IV) reduction activities in aerobic bacteria.