# Bacterial community responses to micropollutants in chemically stressed small rivers in Kenya using environmental DNA

## TL;DR

This study explores how bacterial communities in Kenyan rivers respond to chemical pollution from different land uses.

## Contribution

The study introduces bacterial community composition as a more sensitive indicator of chemical pollution than alpha-diversity in small rivers.

## Key findings

- Bacterial community composition is more sensitive to chemical pollution than alpha-diversity.
- Nutrients and chemical stress explain differences in bacterial communities across land-use types.
- Bacterial degradation potential declines seasonally in all four rivers.

## Abstract

The responses of bacterial communities to changing environmental conditions are manifold but can include structural as well as functional alterations depending on the environmental stressors and toxic chemicals they are exposed to (e.g. pharmaceuticals, personal care products, pesticides, and industrial chemicals). In this study, environmental DNA was extracted from surface water samples collected from four small rivers in the Lake Victoria South Basin (Western Kenya) to (i) evaluate whether alpha- and beta-diversity change in dependency of land-use types, (ii) identify the environmental variables that explain alterations in community structure, (iii) qualitatively and quantitatively assess the consequences of antimicrobial stress on bacterial communities, and (iv) evaluate bacterial functional changes related to the degradation of organic chemicals. Our findings suggest that bacterial community composition is a more sensitive indicator to reflect the impact of chemical pollution derived from different types of land use compared to alpha-diversity. Nutrients and stress from chemical pollution were the variables explaining the dissimilarities between bacterial communities in small, forested, urbanised, and agricultural rivers. Furthermore, an assessment of potential ecological functions associated with the biodegradation of toxic chemicals unveiled a season-specific decline in bacterial degradation potential in all four rivers.

Bacterial community composition in Lake Victoria South Basin rivers proved a more sensitive indicator of chemical pollution from varying land use than alpha-diversity, with nutrients and chemical stress explaining community differences and biodegradation potential showing seasonal declines.