# Stress-induced enrichment of Pseudomonas sp. stimulates the adaptive response of Auxenochlorella pyrenoidosa and antibiotic-resistant proliferation

## TL;DR

This study shows how stress from pollutants promotes a mutualistic relationship between algae and bacteria, especially Pseudomonas, through vitamin B6.

## Contribution

Discovers a vitamin B6-mediated mutualism between algae and antibiotic-resistant bacteria under pollutant stress.

## Key findings

- A. pyrenoidosa's growth and metabolism were enhanced under florfenicol and PLA MPs stress.
- Pseudomonas enrichment promoted ARG transmission without horizontal gene transfer.
- Vitamin B6 secreted by Pseudomonas supports algal survival under stress.

## Abstract

The phycosphere is an important ecological niche for bacteria and antibiotic resistance genes (ARGs). However, whether and how the interaction between microalgae and bacteria changed, and its further effect on the transmission of ARGs under pollutant stress remains enigmatic. Here, Auxenochlorella pyrenoidosa was co-cultured with bacteria screened from lake water to explore the algal–bacteria interaction and ARGs’ transmission in the presence of florfenicol (FF) and polylactic acid microplastics (PLA MPs).

Our study demonstrated that the growth and metabolism of A. pyrenoidosa were promoted under FF treatment or co-treatment with PLA MPs, validated by phenotypic, transcriptome, and metabolome analyses. In contrast, the abundance of phycospheric bacteria was decreased as a result of niche competition. Nonetheless, the transmission of ARGs in the phycosphere was promoted due to the enrichment of antibiotic-resistant bacteria, especially Pseudomonas, rather than horizontal gene transfer. The algal-bacteria co-culture experiment further suggested that vitamin B6 secreted by Pseudomonas sp. likely contributes to underpinning A. pyrenoidosa’ survival under FF and PLA MPs stress.

These findings underscore the dynamic interplay and co-evolution between algae and bacteria under pollutant exposure, and reveal a potential mechanism of vitamin B6-mediated mutualism. This study provides new insights into the assembly of phycospheric bacterial communities and the adaptive strategies of microalgae in contaminated aquatic environments.

Video Abstract

Video Abstract

The online version contains supplementary material available at 10.1186/s40168-026-02335-7.