Bentazone stress resistance in Methylocystis-Tetradesmus symbiosis: Biochemical and communicative exchanges

Methane-oxidizing bacteria (MOB)-microalgae symbiosis is vital for greenhouse gas and carbon regulation in shallow aquatic ecosystems (e.g., rice paddies). However, the effects of pesticide exposure on these non-target species and their stress-induced microbial interactions remain poorly understood. In this study, the widely used pesticide bentazone (BTZ), known to occur at concentrations ranging from background levels to higher values (e.g., up to 100 mg/L) in specific contaminated scenarios like agricultural wastewater, was employed as a model stressor to investigate its effects on the symbiotic system formed by Methylocystis bryophila (M. bryophila) and Tetradesmus obliquus (T. obliquus). Results showed that while BTZ exposure (tested at 10-30 mg/L) inhibited key processes like cell proliferation, methane oxidation, and photosynthesis in individual species, the symbiotic system exhibited significantly enhanced resilience. This resilience stemmed from synergistic interactions, including: facilitated gas exchange promoting metabolic recovery; altered metabolic coupling (e.g., MOB porphyrin supporting algal chlorophyll, algal use of MOB-derived acetate); enhanced intercellular exchange of nutrients and protective extracellular polymeric substances formation; and strengthened physical association via algal metabolites promoting bacterial aggregation and mass transfer. This study elucidates key biochemical and communication mechanisms driving enhanced stress tolerance in MOB-microalgae symbiosis, highlighting the crucial role of microbial interactions in mitigating pesticide impacts in aquatic environments.