Insights into the Function and Horizontal Transfer of Isoproturon Degradation Genes () in a Biobed System.

Biobeds, designed to minimize pesticide point source contamination, rely mainly on biodegradation processes. We studied the interactions of a biobed microbial community with the herbicide isoproturon (IPU) to explore the role of the gene, encoding the large subunit of an -demethylase responsible for the initial demethylation of IPU, via quantitative PCR (qPCR) and reverse transcription-PCR (RT-qPCR) and the effect of IPU on the diversity of the total bacterial community and its active fraction through amplicon sequencing of DNA and RNA, respectively. We further investigated the localization and dispersal mechanisms of in the biobed packing material by measuring the abundance of the plasmid pSH (harboring ) of the IPU-degrading sp. strain SH (previously isolated from the soil used in the biobed) compared with the abundance of the gene and metagenomic fosmid library screening. abundance and expression increased concomitantly with IPU mineralization, verifying its major role in IPU transformation in the biobed system. DNA- and RNA-based 16S rRNA gene sequencing analysis showed no effects on bacterial diversity. The -harboring plasmid pSH showed a consistently lower abundance than , suggesting the localization of in replicons other than pSH. Metagenomic analysis identified four -carrying fosmids. In three of these fosmids, the genes were organized in a well-conserved operon carried by sphingomonad plasmids with low synteny with pSH, while the fourth fosmid contained an incomplete cassette localized in a genomic fragment of a strain. Further analysis suggested a potentially crucial role of IS and IS in the transposition and activation of the operon. Our study provides novel insights into the interactions of IPU with the bacterial community of biobed systems, reinforces the assumption of a transposable nature of IPU-degrading genes, and verifies that on-farm biobed systems are hot spots for the evolution of pesticide catabolic traits.