Objective This study aimed to isolate the potential thiamethoxam-degrading bacteria from coral and to analyze their degradation-related characteristics.

Method Coral samples were used as the experimental material, the symbiotic microorganisms from corals were enriched and cultured for three rounds in a medium with thiamethoxam served as the sole carbon source. The diversity, richness, and community composition of the enriched microbial cultures were analyzed using high-throughput sequencing. The potential thiamethoxam-degrading strains were isolated, identified, and their thiamethoxam-degrading ability was evaluated to determine the target thiamethoxam-degrading strains. The degradation-related characteristics of thiamethoxam of the target strain by identifying degradation products of thiamethoxam and predicting their toxicity.

Result Following three rounds of enrichment culture with thiamethoxam, coral symbionts that could utilize thiamethoxam as the sole carbon source were obtained high-throughput sequencing analysis of the enriched cultures revealed that their community structure of coral symbiotic thiamethoxam-degrading microorganisms.gained complexity with time. Further analysis revealed that within three rounds of enrichment, Proteobacteria, Firmicutes, Bacteroidota and Actinobacteriota were the dominant phyla; γ- and α-Proteobacteria were the predominant classes; Vibrio, Alteromonas and Epibacterium emerged as the preeminent genera. In total, 27 potential thiamethoxam-degrading strains were isolated from the third enrichment culture. Of these, four strains including GXU 22002, GXU 22003, GXU 22031, and GXU 22040 were screened morphologically. By comparing the 16S rRNA sequences, they were identified as Serratia marcescens, Vibrio sagamiensis, V. neocaledonicus and V. alginolyticus, respectively. The thiamethoxam-degradation ability tests indicated that these strains exhibited varying levels of degradation activity. S. marcescens GXU 22002, V. sagamiensis GXU 22003, V. neocaledonicus GXU 22031, and V. alginolyticus GXU 22040 had degradation rates of 14.7%, 16.3%, 20.7%, and 9.9%, respectively, after 7 days. An analysis of the thiamethoxam-degradation products by GXU 22003 confirmed the presence of four main degradation products: TMX-urea, TMX-NH, H-CLO-tri, and CLO-tri. An assessment by the ECOSAR software showed that the acute toxicity of the products against three aquatic organisms (fish, daphnia, and green algae) was weaker than that of the parent compound, thiamethoxam.

Conclusion This study isolated potential thiamethoxam-degrading bacteria from coral samples, and determined their degradatio--associated characteristics, thereby providing valuable resource strains and a theoretical foundation for the control of pesticide pollution.