Impact of salinity shifts on microbial communities from the Warnow River

Several studies investigated the effect of salinity on the distribution and composition of bacterial communities and came to the result that salinity is the most influential factor shaping microbial community composition in natural systems. However, only a few studies have examined the effect of direct salt addition to bacterial freshwater communities. Here I provide the analysis of the effect of three different salinities (4, 8 and 11 PSU) to the freshwater bacterial community of the Warnow River for a duration of three weeks. The bacterial communities of the different treatments and the untreated controls were analyzed using high throughput sequencing data of the 16S DNA processed with the SILVAngs pipeline to examine their composition and diversity. Bacterial community composition showed an increasing abundance of Proteobacteria with rising salinity, contrary Actinobacteria declined at higher salinity levels. Bacteroidetes had a high abundance, unaffected by different salinity levels. Shannon-diversity and evenness increased with rising salinity, whereas species richness had an opposite trend. Additionally, general bacterial abundance and bacterial production were examined using flow cytometry and 3H-thymidine incorporation, respectively. Both were positively affected by increasing salinity on the first days of the experiment, however, no major differences between the treatments could be observed. Altogether, this study supports previous findings that salinity has a strong effect on the composition of bacterial communities and is a shaping factor for bacterial abundance.