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 (LQ15WT and AIY15WT) were isolated from freshwater lakes on the Tibetan Plateau. Comparisons based on the 16S rRNA gene sequences showed that both strains LQ15WT and AIY15WT share 16S rRNA gene sequence similarities 98.4 % with Aquiflexum aquatile Z0201T, but only about 95.0 % with Aquiflexum balticum DSM 16537T. The 16S rRNA gene sequence similarity between strains LQ15WT and AIY15WT was 98.9 %. The phylogenetic tree reconstructed based on 16S rRNA gene sequences also showed that strains LQ15WT and AIY15WT take A. aquatile Z0201T 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 LQ15WT, AIY15WT and A. aquatile Z0201T still formed a close cluster, and A. balticum DSM 16537T and Aquiflexum lacus CUG 91378T formed another cluster. The calculated OrthoANIu, average amino acid identity and digital DNA–DNA hybridization values among strains LQ15WT, AIY15WT, A. aquatile Z0201T, A. balticum DSM 16537T and A. lacus CUG 91378T were less than 91.0, 92.9 and 42.1 %, respectively. The major respiratory quinones of both strains LQ15WT and AIY15WT were MK-7 (32 %) and MK-8 (68 %), and their major fatty acids were iso-C15 : 0, C18 : 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 AIY15WT also contained phosphatidylglycerol and unidentified glycolipid. Considering the distinct phylogenetic relationships and chemotaxonomic characteristics between strains A. aquatile Z0201T and A. balticum DSM 16537T, it is proposed to reclassify A. aquatile into a novel genus Cognataquiflexum gen. nov. as Cognataquiflexum aquatile comb. nov., and strains LQ15WT and AIY15WT should represent two independent novel species of the genus Cognataquiflexum, for which the names Cognataquiflexum nitidum sp. nov. (type strain: LQ15WT=CICC 24711T=JCM 34222T) and Cognataquiflexum rubidum sp. nov. (type strain: AIY15WT=CICC 24708T=JCM 34612T) are proposed.