title: Evolution and adaptation of SAR11 and Cyanobium in a saline Tibetan lake.
abstract: Lake Qinghai is a unique lacustrine ecosystem located on the Tibetan Plateau and exhibits oligotrophic, alkaline, and saline conditions. Previous studies have focused on the community phylogenetic diversity of bacterioplankton in the ecosystem. This study aimed to address the ecotype diversity of bacterioplankton populations in the unique microbial habitat, using metagenomic sequencing and analysis. Phylogenetic analysis revealed two major bacterial populations: SAR11 IIIa (14% of the total) and Cyanobium (14%). Although the two populations shared high 16S rRNA gene sequence identity (> 98% identity) with their closest marine counterparts, they displayed substantial genomic divergence (≤ 80% average amino acid sequence identity). Comparative genomic analysis identified conservation of carbon and energy storage metabolism (biosynthesis of polyphosphate and polyhydroxyalkanoate) gene operons in the SAR11 IIIa and a cyanate (potential nitrogen source in alkaline conditions) transporter gene operon in the Cyanobium. We further identified genetic signature of positive selection acting on an exodeoxyribonuclease gene of the SAR11 IIIa population, which is potentially associated with DNA repair responsive to strong UV radiation on the high altitude mountain. Taken together, our results revealed the ecosystem-specific gene content of the bacterioplankton populations and provided new insights into their adaptations unique to the Tibetan lake.
authors.affiliation: School of Civil and Environmental Engineering, Nanyang Technological University, Singapore, Singapore.|Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
authors.forename: Seungdae
authors.initials: S
authors.lastname: Oh
authors.affiliation: State Key Laboratory of Marine Environmental Science, Xiamen University, Fuijan, China.|Institute of Marine Microbes and Ecospheres, Xiamen University, Fuijan, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China.
authors.forename: Qinglong L
authors.initials: QL
authors.lastname: Wu
authors.affiliation: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
authors.forename: Wen-Tso
authors.initials: WT
authors.lastname: Liu