Proposal to reclassify Aquiflexum aquatile into a novel genus as Cognataquiflexum aquatile gen. nov., comb. nov., and description of Cognataquiflexum nitidum sp. nov. and Cognataquiflexum rubidum sp. nov., isolated from freshwater lakes on the Tibetan Plateau

Thousands of lakes harbouring different characteristics (pH, salinity, temperature) are located on the Tibetan Plateau, and the mining of microbial resources inhabited in these lakes has great value. Two Gram-stain-negative, aerobic, rod-shaped, non-motile strains (LQ15W^T and AIY15W^T) were isolated from freshwater lakes on the Tibetan Plateau. Comparisons based on the 16S rRNA gene sequences showed that both strains LQ15W^T and AIY15W^T share 16S rRNA gene sequence similarities 98.4 % with Aquiflexum aquatile Z0201^T, but only about 95.0 % with Aquiflexum balticum DSM 16537^T. The 16S rRNA gene sequence similarity between strains LQ15W^T and AIY15W^T was 98.9 %. The phylogenetic tree reconstructed based on 16S rRNA gene sequences also showed that strains LQ15W^T and AIY15W^T take A. aquatile Z0201^T as their closest neighbour and these three strains form a tight cluster. In the phylogenomic tree, the genus Aquiflexum was splited into two clusters by Mariniradius saccharolyticus. Strains LQ15W^T, AIY15W^T and A. aquatile Z0201^T still formed a close cluster, and A. balticum DSM 16537^T and Aquiflexum lacus CUG 91378^T formed another cluster. The calculated OrthoANIu, average amino acid identity and digital DNA-DNA hybridization values among strains LQ15W^T, AIY15W^T, A. aquatile Z0201^T, A. balticum DSM 16537^T and A. lacus CUG 91378^T were less than 91.0, 92.9 and 42.1 %, respectively. The major respiratory quinones of both strains LQ15W^T and AIY15W^T were MK-7 (32 %) and MK-8 (68 %), and their major fatty acids were iso-C_15 : 0, C_18 : 1  ω9c, summed feature 3 and summed feature 9. The predominant polar lipids of both strains were phosphatidylethanolamine, unidentified aminophospholipids, unidentified phospholipids and lipids. Strain AIY15W^T also contained phosphatidylglycerol and unidentified glycolipid. Considering the distinct phylogenetic relationships and chemotaxonomic characteristics between strains A. aquatile Z0201^T and A. balticum DSM 16537^T, it is proposed to reclassify A. aquatile into a novel genus Cognataquiflexum gen. nov. as Cognataquiflexum aquatile comb. nov., and strains LQ15W^T and AIY15W^T should represent two independent novel species of the genus Cognataquiflexum, for which the names Cognataquiflexum nitidum sp. nov. (type strain: LQ15W^T=CICC 24711^T=JCM 34222^T) and Cognataquiflexum rubidum sp. nov. (type strain: AIY15W^T=CICC 24708^T=JCM 34612^T) are proposed.

Pararhodonellum marinum gen. nov., sp. nov., isolated from deep-sea sediment

A Gram-stain-negative, non-motile bacterial strain, designated SW124^T, was isolated from a deep-sea sediment sample collected from the Indian Ocean. SW124^T was aerobic and catalase-positive. The strain grew at 4-40 °C (optimum, 30 °C), at pH 5.0-8.6 (optimum, pH 7.0) and in the presence of 0.5-9.5 % (w/v) NaCl (optimum, 3.0%). The results of comparative analyses of the 16S rRNA gene sequence indicated that SW124^T was grouped in the vicinity of the genus Rhodonellum in the family Cyclobacteriaceae. The quinone system contained menaquinone MK-7. The predominant cellular fatty acids were iso-C_15 : 0, iso-C_17 : 0 3-OH and summed feature 3 (comprising C_16 : 1ω7c and/or C_16 : 1ω6c). SW124^T contained phosphatidylethanolamine (PE) as the major polar lipid. The genomic DNA G+C content of SW124^T was 41.7 mol%. On the basis of its phenotypic characteristics and phylogenetic data, we propose that strain SW124^T (=CGMCC 1.16171^T=KCTC 82235^T) represents a novel species of a novel genus, with the name Pararhodonellum marinum gen. nov., sp. nov.

Aquiflexum lacus sp. nov., isolated from a lake sediment sample

A novel Gram-staining negative, crescent-like or rod-shaped, non-motile bacterium, designated strain CUG 91378 ^T, was isolated from a sediment sample of Qinghai Lake, Qinghai Province, China. The strain was red-colored, and catalase- and oxidase-positive. Strain CUG 91378 ^T was able to grow at 15-37 °C (optimum, 28 °C), pH 7-9 (pH 7.0) and in the presence of up to 3.0% (w/v) NaCl (0-2%). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain CUG 91378 ^T formed a well-supported monophyletic clade with Aquiflexum balticum DSM 16537 ^T (95.4%) and Aquiflexum aquatile Z0201^T (93.2%). The DNA G + C content of CUG 91378 ^T was 39.0%. Low (< 87%) average nucleotide identity (ANI) and (< 26%) digital DNA-DNA hybridization (dDDH) values were observed between strain CUG 91378 ^T and its closest species on the phylogenetic trees. The sole respiratory quinone of strain CUG 91378 ^T was MK-7. The predominant fatty acids (> 5.0%) were iso-C_15:0 (19.1%), iso-C_16:0 (12.0%), iso-C_16:1 H (10.9%), iso-C_16:0 3OH (9.2%), iso-C_17:0 3OH (7.7%), C_17:1ω6c (6.1%) and anteiso-C_15:0 (5.8%). Strain CUG 91378 ^T contained as phosphatidylethanolamine (PE), phosphatidylglycerol (PG) and four unidentified lipids (L1, L2, L3 and L4). Based on the data from the current polyphasic study, the isolate represents a novel species of the genus Aquiflexum for which the name Aquiflexum lacus is proposed. The type strain of the proposed new taxon is CUG 91378 ^T (= KCTC 62637 ^T = CGMCC 1.13988 ^T).