# Cascade Responses of Microbial Communities To Alcohols and Organic Acids in a Marine Microcosm Experiment

## TL;DR

This study shows how alcohols and organic acids from pollution affect marine microbes, revealing that even low concentrations can cause significant ecological changes.

## Contribution

The study introduces a novel microcosm approach to observe microbial cascades in response to organic pollutants in marine sediments.

## Key findings

- At 0.5% concentration, 469 microbial variants formed two enrichment cascades.
- At 0.05% concentration, 576 variants formed three cascades with greater functional diversity in late responders.
- Lower pollutant concentrations caused stronger ecological effects, supporting energy-driven diversification theory.

## Abstract

Alcohols and organic acids are major energy-rich components of sewage, and marine environments are significant recipients of these pollutants. However, their effects on marine microbial communities remain poorly understood. Recent theoretical models suggest that high energy inputs can disrupt microbial networks that have evolved under energy-limited conditions. The aim of our study was to determine the community-level effects of two alcohols (ethanol and methanol) and two organic acids (acetate and succinate) using a marine microcosm time-series experiment. We tested three sediment types: one impacted by sewage, one by aquaculture, and one unimpacted. The tested concentrations were 0.05% and 0.5%. At 0.5%, we identified 469 sequence variants (determined from 16 S rRNA gene sequencing) with more than a twofold increase during the experiment, grouped into two enrichment cascades. At 0.05%, 576 sequence variants responded, forming three cascades. Late-appearing sequence variants showed greater inferred functional diversity than early responders. The stronger effects observed at lower concentrations support the theory that energy conservation drives microbial diversification, indicating that even low-level pollution can cause significant ecological changes. These findings highlight the importance of considering microbial community responses in environmental impact assessments of organic pollution in marine ecosystems.

The online version contains supplementary material available at 10.1007/s00284-025-04581-8.