Investigating the horizontal transmissibility of bacterial metaldehyde and metazachlor-degrading genes

The molluscicide metaldehyde and the herbicide metazachlor have been detected in surface waters previously, posing risks to drinking water quality and the health of humans and wildlife. Soil-derived bacterial strains can degrade metaldehyde, a trait which was acquired by inferred horizontal gene transfer. The metaldehyde-degrading genes and plasmids responsible could be further disseminated to other bacterial strains by horizontal gene transfer. Novel pathways for the metaldehyde biodegradation process were also said to exist. In comparison, much less was known about the microbial biodegradation of metazachlor; however, it was predicted to occur in soils facilitated by bacterial glutathione conjugation by glutathione transferases. In vitro and soil microcosm-based facilitated horizontal gene transfer, selective enrichment, whole genome sequencing and bioinformatics approaches were employed to investigate the hypothesis that horizontal gene transfer processes could be harnessed experimentally to identify novel metaldehyde and metazachlor-degrading organisms, genes and metabolic pathways, and to demonstrate the horizontal transmissibility of metaldehyde and metazachlor-degrading genes. Two novel metaldehyde-degrading Acinetobacter calcoaceticus strains, 5.1 and 6.6, were isolated from allotment soils inoculated with the non-degrading bacterial strain Acinetobacter calcoaceticus RUH 2202. Two candidate metaldehyde-degrading genes, 15 and 2947, were identified in both strains. Additionally, three novel metazachlor-degrading Pseudomonas strains, 4.2.2, 4.5.2 and 6.4.2, were isolated from agricultural soils. Glutathione transferase enzymes, gstB_1, gstB_2, yibF, 4164, 3838 and 4909, were identified as candidate metazachlor-degrading genes. These findings lay the groundwork for further investigations into microbial biodegradation and bioremediation of metaldehyde and metazachlor. The methodological approach used could also provide valuable insights for future research on microbial xenobiotic biodegradation and horizontal gene transfer.