Metal stressors consistently modulate bacterial conjugal plasmid uptake potential in a phylogenetically conserved manner

Abstract

The environmental stimulants and inhibitors of conjugal plasmid transfer in microbial communities are poorly understood. Specifically, it is not known whether exposure to stressors may cause a community to alter its plasmid uptake ability. We assessed whether metals (Cu, Cd, Ni, Zn) and one metalloid (As), at concentrations causing partial growth inhibition, modulate community permissiveness (that is, uptake ability) against a broad-host-range IncP-type plasmid (pKJK5). Cells were extracted from an agricultural soil as recipient community and a cultivation-minimal filter mating assay was conducted with an exogenous E. coli donor strain. The donor hosted a gfp-tagged pKJK5 derivative from which conjugation events could be microscopically quantified and transconjugants isolated and phylogenetically described at high resolution via FACS and 16S rRNA amplicon sequencing. Metal stress consistently decreased plasmid transfer frequencies to the community, while the transconjugal pool richness remained unaffected with OTUs belonging to 12 bacterial phyla. The taxonomic composition of the transconjugal pools was distinct from their respective recipient communities and clustered dependent on the stress type and dose. However, for certain OTUs, stress increased or decreased permissiveness by more than 1000-fold and this response was typically correlated across different metals and doses. The response to some stresses was, in addition, phylogenetically conserved. This is the first demonstration that community permissiveness is sensitive to metal(loid) stress in a manner that is both partially consistent across stressors and phylogenetically conserved.

Regulation of conjugative transfer of plasmids and integrative conjugative elements

“…Also, although the general tendency was to decrease transfer, for some specific OTUs transfer did actually increase. Overall, these results indicate a profound effect of metal-caused stress on conjugative transfer, measured as permissiveness, which has been defined as "the ability of a community to receive a plasmid, both in terms of transfer frequency and phylogeny" (Klumper et al, 2017).…”

“…A more recent report of coexistence and possible dissemination of multidrug and metal resistant plasmids was published by Fang et al, (2016). In a very elegant manner, Klumper et al, (2017) have shown that the presence of low concentrations of metal stressors such as Zn, Cd, Cu, Ni and As decreased the transfer of a broad-host-range IncP-type plasmid (pKJK5) to potential recipients extracted from an agricultural soil, however, transconjugants were distributed among 12 different bacterial phyla, indicating that the distribution pattern was unaffected. Also, although the general tendency was to decrease transfer, for some specific OTUs transfer did actually increase.…”

Zinc can counteract selection for ciprofloxacin resistance

“…Metal stress could for 303 example increase the rate at which antibiotic and metal resistance evolves through 304 increased mutation rate (Lemire, Harrison and Turner 2013), which could subsequently be 305 fixed in the population through antibiotic or metal selection. Increased spread of resistance 306 could also result from metals impacting plasmid transfer (Klümper et al 2017(Klümper et al , 2019a. 307…”

Non-antibiotic pharmaceuticals can enhance the spread of antibiotic resistance via conjugation

“…Therefore, these studies on animals or humans support the increase in ROS in the presence of these non-antibiotic pharmaceuticals. In addition to these non-antibiotic pharmaceuticals, biocides (e.g., triclosan) and heavy metals were also demonstrated to increase ROS generation levels, impose stress-response on bacteria, thus enhancing the uptake potential of conjugal plasmids 60–62 . Further studies are required to confirm if other non-antibiotic pharmaceuticals follow this pattern of enhancing intracellular ROS generation and potentially contributing to increased bacterial gene transfer.…”