Coevolution of Plasmids in Bacteria Evolved in Biofilm and Chemostat Cultures

Broad-host range (BHR) plasmids are one of the main vectors of the spread of antibiotic resistance across bacteria, a major health concern today. In well-mixed cultures, BHR plasmids can become more persistent in bacterial populations after a short period of co-evolution under plasmid selection. However, these experimental conditions do not mimic those found in 80% of bacterial infections, wherein bacteria grow in biofilms. Biofilms are known to retain genetic diversity within the bacterial population. We hypothesized that when plasmid-host pairs are coevolved in a biofilm, they will exhibit a broader range of persistence level than when coevolved in a well-mixed culture. A BHR plasmid was coevolved in the host Shewanella oneidensis MR1 for 28 days in biofilm and well-mixed culture environments. The persistence of the coevolved plasmid in their host was assessed for 3 clones isolated from each condition. Preliminary data suggests that when coevolved in a biofilm, the plasmid became more persistent than when coevolved in well-mixed environment. In order to confirm this result, more clones from several independent replicate assays are currently under investigation.