Both pH and salinity shape the microbial communities of the lakes in Badain Jaran Desert, NW China

Badain Jaran Desert (BJD), characterized by extremely arid climate and tallest sand dunes in the world, is the second largest desert in China. Surprisingly, there are a large number of permanent lakes in this desert. At present, little is known about the composition and distribution of microbial communities in these desert lakes, which are an important bioresource and play a fundamental role in the elemental cycles of the lakes. In this study, the physicochemical characteristics and microbial communities of water samples from 15 lakes in BJD were comparatively investigated. The results showed that the lakes were rich in Na⁺, Cl^-, CO₃^2- and HCO₃^- while Ca²⁺ and Mg²⁺ were scarce, with pH 8.52-10.27 and salinity 1.05-478.70 g/L. Bacteria dominated exclusively in low saline lakes (salinity < 50 g/L) while archaea were predominant in hypersaline lakes (salinity > 250 g/L), which abundance increased along salinity gradient linearly. Genera Flavobacterium, Synechocystis and Roseobacter from phyla Bacteroidetes, Cyanobacteria, Alphaproteobacteria were the major members in low saline lakes whereas Halomonas, Aliidiomarina and Halopelagius from Gammaproteobacteria and Euryarchaeota were abundant in moderately saline lakes (salinity 50-250 g/L). The hypersaline lakes were predominated by extreme halophiles such as Halorubrum, Halohasta and Natronomonas from Euryarchaeota. The correlation among the microbes in the lakes was mainly positive, suggesting they can survive in the harsh environments through synergistic interactions. Statistical analyses indicated that physicochemical characteristics rather than spatial factors shaped the microbial communities in the desert lakes. The pH was the most important environmental factor controlling alpha diversity, while salinity was the major driver determining microbial community structure in BJD lakes. In contrast, geographic factors had no significant impact on the microbial community compositions.