Variation of bacterial communities along the vertical gradient in Lake Issyk Kul, Kyrgyzstan

Abstract

30In this study, we explored the diversity and community composition of bacteria along a 31 vertical gradient in Lake Issyk Kul, Kyrgyzstan, one of the largest and deepest brackish lakes 32 in in the world. We identified 4904 bacterial ASVs based on analysis of 16S rRNA gene 33 sequences and determined significant changes in the composition responding mainly to the 34 variables depth and salinity. A higher abundance of Proteobacteria and Bacteroidetes was 35 observed in the surface waters and the lake tributaries. Cyanobacteria were more abundant in 36 the deep chlorophyll maximum (28.5 to 128 m), while Planctomycetes and Chloroflexi were 37 dominant at depths between 128 to 600 m. According to our machine learning analysis used 38 for identifying the most critical environmental factors, depth and temperature revealed the 39 strongest effect on members of Proteobacteria, Planctomycetes, and Chloroflexi, while 40 oxygen is associated with the variations in Cyanobacteria. Also, a notable increase in alpha 41 diversity estimations was observed with increasing water depth. This work evidences 42 significant differences in the structure of bacterial communities along the depth gradient in 43 deep, transparent lake ecosystems. Notably, there is a dominance of Planctomycetes and 44

Stratification in Microbial Communities with Depth and Redox Status in a Eutrophic Lake Across Two Years

“…The most coarse taxonomic level, phylum, was a natural starting point to visualize the most general trends in the microbiome. The relative abundance of phyla has been shown to change dramatically with depth in several other depth-discrete sampling studies (Tran et al 2021;Rojas-Jimenez et al 2021;Baatar et al 2016;Garcia et al 2013). These changes in phyla are often attributed to the redox gradients throughout the water column (Jones, Newton, and McMahon 2009;Wu and Hahn 2006;Newton et al 2007;Garcia et al 2013) .…”

“…Several of these studies include investigating microbial communities along redox gradients (Garcia et al 2013;Small et al 2014;Rojas-Jimenez et al 2021).…”

“…Dimitic lakes with an anoxic hypolimnion pose an especially interesting study system as the biannual mixing events cause the formation of temporary redox gradients. These gradients have been shown to facilitate the growth of a diverse microbial community (Garcia et al 2013;Rojas-Jimenez et al 2021). With the seasonal mixing and reforming of the redox gradient, the microbes also shape the environmental conditions as the lake stratification continues (Yu et al 2014;Morrison et al 2017).…”