Differential expression of a prophage-encoded glycocin and its immunity protein suggests a mutualistic strategy of a phage and its host

Emma L Denham,Ewoud Reilman,Jan Maarten Van Dijl,Marcus C De Goffau,Sjouke Piersma,Marleen Rinket

doi:10.1038/s41598-019-39169-3

Abstract

Sublancin 168 is a highly potent and stable antimicrobial peptide secreted by the Gram-positive bacterium Bacillus subtilis. Production of sublancin gives B. subtilis a major competitive growth advantage over a range of other bacteria thriving in the same ecological niches, the soil and plant rhizosphere. B. subtilis protects itself against sublancin by producing the cognate immunity protein SunI. Previous studies have shown that both the sunA gene for sublancin and the sunI immunity gene are encoded by the prophage SPβ. The sunA gene is under control of several transcriptional regulators. Here we describe the mechanisms by which sunA is heterogeneously expressed within a population, while the sunI gene encoding the immunity protein is homogeneously expressed. The key determinants in heterogeneous sunA expression are the transcriptional regulators Spo0A, AbrB and Rok. Interestingly, these regulators have only a minor influence on sunI expression and they have no effect on the homogeneous expression of sunI within a population of growing cells. Altogether, our findings imply that the homogeneous expression of sunI allows even cells that are not producing sublancin to protect themselves at all times from the active sublancin produced at high levels by their isogenic neighbors. This suggests a mutualistic evolutionary strategy entertained by the SPβ prophage and its Bacillus host, ensuring both stable prophage maintenance and a maximal competitive advantage for the host at minimal costs.

Highlights

The fitness of bacterial cells and populations belonging to a particular species is critically dependent on their ability to compete with other organisms
Expression of sunA and production of active sublancin on Lysogeny Broth (LB) are determined by the transcriptional regulators Abh, AbrB, Rok, Spo0A, σM and σX
LB was selected for these analyses, because little if any active sublancin is produced when cells are grown on minimal media within the 17 h time frame of our experiments

Summary

Introduction

The fitness of bacterial cells and populations belonging to a particular species is critically dependent on their ability to compete with other organisms. As shown through recent systems biological analyses, B. subtilis has an intricate regulatory architecture that allows it to rapidly and effectively adapt to changing conditions[1,2] This organism has mastered the art of adapting to a wide range of environmental stresses and insults[3,4] and, on top of that, B. subtilis secretes a cocktail of antimicrobial compounds into its environment that is deadly for a wide range of other microbes[5,6]. We show that while multiple regulators influence the levels of sunA expression, the heterogeneity of the sunA promoter (PsunA) activity is controlled by only three of them, namely Spo0A, AbrB and Rok. through analysis of the sunI-GFP promoter fusion we found that the immunity gene sunI is homogeneously expressed in all cells of the investigated population, which will protect them from the toxic effects of sublancin

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