Gut microbiota dynamics associated with the tolerance of chironomid larvae to Microcystis aeruginosa stress

Lei Cao¹Shuqin Yang¹Wenping Wang^1,2*Kun Zhang¹Lei Ji¹Deng Daogui^1*

• ¹School of Life Sciences, Huaibei Normal University, Huaibei, China
• ²State Key Laboratory of Lake and Watershed Science for Water Security, Nanjing, China

Microcystis aeruginosa, a dominant cyanobacterial species in freshwater blooms, produces toxins that pose serious threats to aquatic organisms and human health. However, the role of gut microbiota in mediating chironomid larval tolerance to cyanobacterial stress remains unclear. This study investigated the physiological and gut microbial changes in Propsilocerus akamusi larvae exposed to M. aeruginosa at environmentally relevant densities commonly observed during cyanobacterial blooms (1.0 × 106/107/108/109 cells L-1). The results showed that exposure to M. aeruginosa at 1.0 × 109 cells L-1 significantly suppressed chironomid larvae activity and led to high mortality, while the chironomid larvae exhibited certain tolerance at lower densities, with notably enhanced tolerance at 1.0 × 108 cells L-1, suggesting that this density may effectively trigger the tolerance mechanism of chironomid larvae to M. aeruginosa. High-throughput sequencing of 16S rRNA revealed a significant increase in the diversity of gut microbiota in chironomid larvae under lower densities of M. aeruginosa stress, especially 1.0 × 108 cells L-1. Combined with interaction network analysis, it was demonstrated that key bacterial genera (e.g., Cutibacterium, Epulopiscium, Methylobacterium and Sphaerotilus) associated with processes like toxin degradation, maintenance of intestinal homeostasis, and regulation of stress responses were significantly associated with tolerance of chironomid larvae to cyanobacterial stress, and there may be a synergistic effect among these key bacterial genera. Conversely, gas-producing, toxigenic, and pathogenic bacterial taxa (e.g., Carnobacterium, Clostridium and Aeromonas) increases were significantly correlated with the mortality of chironomid larvae under cyanobacterial stress. Furthermore, interactions between eukaryotic microorganisms (e.g., Opisthokonta and Alveolata) and Paucibacter may also participated in the regulation for chironomid larvae tolerance to M. aeruginosa. These findings provide new insights into the gut microbiome-mediated adaptive responses of benthic invertebrates to cyanobacterial blooms, and highlight the potential of keystone microbial taxa as ecological indicators or targets for microbiome-based management strategies in bloom-affected aquatic systems. This study also provide a data support for further mechanistic investigations into microbe-mediated host tolerance and the development of microbial-assisted ecological restoration approaches.