ASSESSING MICROBIAL COMMUNITY RESPONSES IN A CHEMICALLY STRESSED FRESHWATER ECOSYSTEM USING ENVIRONMENTAL DNA

Abstract: Microbial communities represent the fundamental cornerstones of riverine ecosystems because they are involved in numerous processes which mediate ecosystem services. However, riverine ecosystems are currently massively altered by a variety of anthropogenic activities which includes changes in landuse and chemical pollution. Particularly, chemicals of emerging concern (CECs) such as pesticides and pharmaceuticals are ubiquitously found in rivers as a consequence of continuous agricultural runoff as well as domestic and industrial sewage discharge. Nonetheless, there is a tremendous lack of knowledge about bacterial communities in lotic environments, especially in developing countries like Kenya. The primary objective of this study was to analyse the structural and functional responses of bacterial communities to environmental parameters, most notably CECs, derived from land-use in five Kenya riverine ecosystems. For this purpose, environmental DNA metabarcoding was applied to take a snapshot of the bacterial community structure in surface water and sediment in two different seasons. Furthermore, to assess the impact of CECs, the antimicrobial toxic stress was calculated for the detected organic chemicals. The main results of this study revealed that the variation in bacterial community structure and functional diversity can primarily be attributed to differences in land-use and their seasonal variability. The measured environmental and chemical parameters, on the other hand, displayed low nutrient load and antimicrobial toxicity in all rivers in both seasons indicating overall uniformity from a chemical perspective. Consequently, antimicrobial stress was unable to adequately explain the significant differences between riverine ecosystems, however, this was mostly attributed to the lack of biological replication, thus statistical power. Ultimately, this study suggests the adaptation of bacterial community composition and ecological functioning to land-use as well as the associated chemical pollution.