Mild Stress Conditions during Laboratory Culture Promote the Proliferation of Mutations That Negatively Affect Sigma B Activity in Listeria monocytogenes
Duarte N. Guerreiro, Jialun Wu, Charlotte Dessaux, Ana H. Oliveira, Teresa Tiensuu, Diana Gudynaite, Catarina Marinho, Aoife Boyd, Francisco Garcı́a-del Portillo, Jörgen Johansson, Conor O’Byrne
Abstract
In the present study, we investigated a collection of Listeria monocytogenes strains that all carried sigB operon mutations. The mutants all had reduced σ B activity and were found to have a growth advantage under conditions of mild heat stress (42°C). In mixed cultures, these mutants outcompeted the wild type when mild heat stress was present but not at an optimal growth temperature. An analysis of 22,340 published L. monocytogenes genome sequences found a high rate of premature stop codons present in genes positively regulating σ B activity. Together, these findings suggest that the occurrence of mutations that attenuate σ B activity can be favored under conditions of mild stress, probably highlighting the burden on cellular resources that stems from deploying the general stress response.