Bacteria elicit a phage tolerance response subsequent to infection of their neighbors

Abstract

Plaque occurrence on a bacterial lawn manifests successive rounds of bacteriophage infection. Yet, mechanisms evolved by bacteria to limit plaque spread have been hardly explored. Here we investigated the dynamics of plaque development by lytic phages infecting the bacterium Bacillus subtilis. We report that plaque expansion is followed by a constriction phase owing to bacterial growth into the plaque zone. This phenomenon is caused by an adaptive process, herein termed "phage tolerance response", elicited by non-infected bacteria located at the plaque rim upon sensing infection of their neighbors. The temporary phage-tolerance is executed by the stress response RNA polymerase sigma factor {sigma}X, primarily through activation of the dlt operon, encoding enzymes that catalyze D-alanylation of cell wall teichoic acid polymers, the major attachment sites for phages infecting Gram-positive bacteria. D-alanylation impedes phage binding and hence infection, thus enabling the uninfected bacteria to form a protective shield opposing plaque spread.