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

Abstract

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.

Keywords: Cognataquiflexum; Tibetan Plateau; freshwater lake.