Loss of the Rhodobacter capsulatus serine acetyl transferase gene, cysE1, impairs GTA gene transfer and biofilm phenotypes

Biofilms are ubiquitous in the environment where they allow bacterial species to survive adverse conditions. Cells in biofilm are densely packed, and this proximity is likely to increase the frequency of horizontal gene transfer. Gene transfer agents (GTAs) are domesticated viruses with the potential to spread any gene between bacteria. GTA production is normally restricted to a small sub-population of bacteria and regulation of GTA loci is highly coordinated, however, the environmental conditions that favour GTA production are poorly understood. Here, we identify a serine acetyltransferase gene, cysE1, in Rhodobacter capsulatus that is required for optimal receipt of GTA DNA, accumulation of extracellular polysaccharide and biofilm formation. The cysE1 gene is directly downstream of the core RcGTA structural gene cluster and upregulated in a RcGTA overproducer strain, although it expressed on a separate transcript. The data we present suggest that GTA production and biofilm are co-regulated, which could have important implications for the study of rapid bacterial evolution and understanding the full impact of GTAs in the environment.