Host infection selects for sRNA variants that drive bacterial social cheating

Here we show that arcZ, encoding a conserved Hfq-dependent sRNA in the plant pathogen Dickeya solani, undergoes recurrent single-nucleotide mutations during potato tuber infection. Five distinct arcZ alleles define a graded series of ArcZ functional impairment in which antifungal and protease activities are progressively reduced while virulence is compromised only in a subset of alleles.

All five variants gain a fitness advantage exclusively during co-infection with wild-type arcZ1 cells, an advantage that is strongest when variants are rare, declines as cheater frequency increases, and correlates with declining total bacterial productivity, the canonical signature of social cheating and a tragedy of the commons.[kp1.1] No fitness benefit is detected in vitro. Transcriptomic profiling of five arcZ variants identifies a conserved core of 132 downregulated genes enriched in secreted and diffusible functions.