Our
understanding of the microorganisms involved in in
situ biodegradation of xenobiotics, like pesticides, in natural
and engineered environments is poor. On-farm biopurification systems
(BPSs) treat farm-produced pesticide-contaminated wastewater to reduce
surface water pollution. BPSs are a labor and cost-efficient technology
but are still mainly operated as black box systems. We used DNA-stable
isotope probing (DNA-SIP) and classical enrichment to be informed
about the organisms responsible for in situ degradation
of the phenylurea herbicide linuron in a BPS matrix. DNA-SIP identified Ramlibacter, Variovorax, and an unknown Comamonadaceae genus
as the dominant linuron assimilators. While linuron-degrading Variovorax strains have been isolated repeatedly, Ramlibacter has never been associated before with
linuron degradation. Genes and mobile genetic elements (MGEs) previously
linked to linuron catabolism were enriched in the heavy DNA-SIP fractions,
suggesting their involvement in in situ linuron assimilation.
BPS material free cultivation of linuron degraders from the same BPS
matrix resulted in a community dominated by Variovorax, while Ramlibacter was not observed.
Our study provides evidence for the role of Variovorax in in situ linuron biodegradation in a BPS, alongside
other organisms like Ramlibacter, and
further shows that cultivation results in a biased representation
of the in situ linuron-assimilating bacterial populations.