Effects of Thermal Stratification on Bacterial Community Composition Throughout Water Column in A Deep Lake

Abstract

This study aimed to assess the effects of stratification on bacterial community structures throughout a water column in the alkaline Lake Iznik. For this purpose, the samples were collected from the deepest point of the lake from three depths representing the thermal layers namely, epilimnion (0.5 m), metalimnion (20 m), and hypolimnion (40 m) in August 2020. 16S rRNA gene-targeted amplicon sequencing approach was used to assess the bacterial community compositions and sequencing was carried out in Illumina® MiSeq™ platform. The temperature (from 25.76 to 9.37°C), EC (from 1035 to 398 µS/cm), and pH (from 9.1 to 7.7) were gradually decreased throughout the water column. While a remarked increase was observed in phosphorous (from 25.75 to 119.72 µg/L) and nitrate (from 94.68 to 167.71 µg/L) levels along with the water column. DO level significantly decreased to 1.04 mg/L in the hypolimnion. The bacterial community in the epilimnion was predominated by Actinobacteria which represented 52% of the total reads and the abundance went down through the water column and the minimum level was recorded in the hypolimnion (28%). Proteobacteria (18%) was the second abundant phylum in the epilimnion followed by Bacteroidetes (12%) and Verrucomicrobia (9%). Proteobacteria became dominant in the hypolimnion and 46% of the bacterial community was represented by Proteobacteria species. Among the classified bacterial families, the majority of the total reads were assigned to Sporichthyaceae, Ilumatobacteraceae, Burkholderiaceae, and Microbacteriaceae in all three samples. The diversity and evenness of the bacterial communities were increased through the water column. This work contributes to existing knowledge of bacterial diversity of stratified lakes by providing high throughput data from a unique alkaline environment.