Abstract:

Aim: Extreme environmental lakes are most densely distributed in the Qinghai-Tibet Plateau (QTP) in China, and the lake types and the hydrochemical characteristics are diverse. However, little is known about the bacterial community composition and diversity of these lakes in the QTP.

Methods: This study was carried out in four hydrochemical types of lakes on the QTP (e.g. chloride type, MgSO₄ subtype, Na₂SO₄ subtype, and carbonate type). Illumina 16S rRNA gene (V₃‒V₄ region) sequencing was used to analyze the bacterial diversity, community composition, and the associations between dominant taxa and environmental factors in the QTP.

Results: The hydrochemical characteristics indicated that two lake groups of MgSO₄ subtype and chloride type belonged to extremely hypersaline environment, while most samples of Na₂SO₄ subtype and carbonate type groups belonged to mesosaline, brackish or fresh water environments. A total of 45 phyla, 81 classes, and 1,148 genera (52,031 OTUs) of bacteria were investigated. The Shannon diversity index of bacteria was carbonate type (5.27 ± 0.57) > Na₂SO₄ subtype (4.96 ± 0.51) > chloride type (4.12 ± 0.80) > MgSO₄ subtype (3.64 ± 1.04). The dominant phyla within the bacterial communities were Proteobacteria, Bacteroidetes, and Firmicutes. The relative abundance of Proteobacteria was high, and the dominant classes were γ-, α- and β-Proteobacteria. Firmicutes mainly distributed in the MgSO₄ subtype and chloride-type lakes, and the dominant class was Bacilli. Bacteroidetes mainly distributed in the carbonate type and Na₂SO₄ subtype lakes, and the dominant class was Flavobacteriia. The bacterial community composition of chloride type lakes was similar to a few samples of MgSO₄ subtype lakes, and the distribution of the dominant genera (Pseudomonas, Lactococcus, and Acinetobacter) positively correlated with the total salinity, main ion (Mg²⁺, Cl^-, Na⁺ and K⁺), and temperature. Among the MgSO₄ subtype lakes, the distribution of the uniquely common genera Bacillus, Aeromonas, and Oceanobacilluspositively correlated with the concentration of SO₄^2-. The bacterial community composition of the Na₂SO₄ subtype lakes was similar to the carbonate type lakes, while the distribution of some dominant genera, e.g. Aquiflexum, Haliea and Luteolibacter, significantly and positively correlated with the environment variables, including HCO₃^-content, altitude, and pH value.

Conclusion: Compared with other lake groups in the world, lakes in the QTP have unique dominant and common bacterial genera. Bacterial community composition varies in different lake types, which may be related to hydrochemical type or geographical location.

Key words: Qinghai-Tibet Plateau, plateau lake, bacteria, biodiversity, hydrochemical characteristic