Gre factors protect against phenotypic diversification and cheating in Escherichia coli populations under toxic metabolite stress

Abstract

Nitric oxide ({middle dot}NO) is one of the toxic metabolites that bacteria can be exposed to within phagosomes. Gre factors, which are also known as transcript cleavage factors or transcription elongation factors, relieve back-tracked transcription elongation complexes by cleaving nascent RNAs, which allows transcription to resume after stalling. Here we discovered that loss of both Gre factors in E. coli, GreA and GreB, significantly compromised {middle dot}NO detoxification through a phenotypic diversification of the population. Under normal culturing conditions, both wild-type and {Delta}greA{Delta}greB synthesized protein uniformly. However, treatment with {middle dot}NO led to bimodal protein expression in {Delta}greA{Delta}greB, whereas wild-type remained unimodal. Interestingly, exposure to another toxic metabolite of phagosomes, hydrogen peroxide (H2O2), produced similar results. We found that the diversification in {Delta}greA{Delta}greB cultures required E. coli RNAP, occurred at the level of transcription, and could produce cheating where transcriptionally-deficient cells benefit from the detoxification activities of the transcriptionally-proficient subpopulation. Collectively, these results indicate that Gre factors bolster bacterial defenses by preventing phenotypic diversification and cheating in environments with fast-diffusing toxic metabolites. ImportanceToxic metabolite stress occurs in a broad range of contexts that are important to human health, microbial ecology, and biotechnology; whereas Gre factors are highly conserved throughout the bacterial kingdom. Here we discovered that the Gre factors of E. coli prevent phenotypic diversification under toxic metabolite stress. Such conformist regulation improves populationwide removal of those stressors and protects against cheating, where one subpopulation commits resources to counter a threat, and the other subpopulation does not, yet both subpopulations benefit.