Conjugal transfer of catabolic plasmids by damaged bacterial cells: Rescuing genes for pesticide biodegradation

Bacterial conjugative plasmids could carry genes involved in pesticide biodegradation. However, its conjugal transfer is affected by stressors such as metals. Our aim was to determine if bacterial cells exposed to copper can transfer by conjugation the catabolic plasmid pRO101 and assessed the expression of traK gene. Cupriavidus pinatubonensis AEO106 and Pseudomonas putida KT2440 were used as donor and recipient strains, respectively. Mating assays were carried out in presence of Cu²⁺ (0.3, 0.8, 1.6, 3.9 or 7.9 mM) or H₂O₂ (0.1, 0.2, 0.5, 1, 2 or 5 mM). The expression of traK gene and the effect of Cu²⁺ on donor cells was determined by RTqPCR and flow cytometry, respectively. Cytoplasmic membrane of 90% of donor cells was damaged by Cu²⁺, but the transference of pRO101 plasmid occurred at a proportion similar to the control. Moreover, traK gene expression was reduced (c.a. 50%) by Cu²⁺. This demonstrated that damaged donor cells were still able to transfer the pRO101 plasmid, allowing a rescue of these genetic material and contribute to self-purifying processes in the environment. Although without ruling out the possibility that transformation occurred, the expression of the traK gene suggested that conjugation occurred between damaged donor cells and recipient cells.