Dynamics of IS1071 and Its Accessory Gene Functions During Start-Up of an On-Farm Biopurification System

Insertion sequences (IS) are drivers of bacterial diversification by facilitating recruitment and horizontal transfer of adaptive genes involving composite transposon structures, but their evolutionary role at the community level is rarely addressed. This study explores the dynamics of IS1071 and the cargo of IS1071-associated putative composite transposons in the establishment of a pesticide-degrading microbiome in an on-farm biopurification system (BPS)-which treats pesticide-contaminated wastewater and is considered a hotspot of microbial evolution-during the crucial start-up phase. Pesticide mineralisation assays and quantitative PCR targeting pesticide catabolic genes showed that the microbial community, upon feeding on the pesticide-contaminated wastewater, rapidly evolved into a pesticide-degrading microbiome. Concomitantly, an increase in the relative abundances of several mobile genetic elements, including IS1071, was observed, as well as a striking enrichment of xenobiotic catabolic genes in the cargo of putative IS1071-flanked composite transposons. The IS1071 cargo catabolic genes diversified over time and were mainly of Betaproteobacterial origin. Clear changes in community composition were observed both in the total bacterial community and the Betaproteobacterial community. We conclude that IS1071 supports the rapid establishment of pesticide catabolism in the BPS microbiome, highlighting the contribution of IS elements to microbial community adaptation to environmental changes.