A single mutation in rapP induces cheating to prevent cheating in Bacillus subtilis by minimizing public good production

Abstract

Cooperation is beneficial to group behaviors like multicellularity, but is vulnerable to exploitation by cheaters. Here we analyze mechanisms that protect against exploitation of extracellular surfactin in swarms of Bacillus subtilis. Unexpectedly, the reference strain NCIB 3610 displays inherent resistance to surfactin-non-producing cheaters, while a different wild isolate is susceptible. We trace this interstrain difference down to a single amino acid change in the plasmid-borne regulator RapP, which is necessary and sufficient for cheater mitigation. This allele, prevalent in many Bacillus species, optimizes transcription of the surfactin operon to the minimum needed for full cooperation. When combined with a strain lacking rapP, NCIB 3610 acts as a cheater itself—except it does not harm the population at high proportions since it still produces enough surfactin. This strategy of minimal production is thus a doubly advantageous mechanism to limit exploitation of public goods, and is readily evolved from existing regulatory networks.

Transcriptional Regulation and Mechanism of SigN (ZpdN), a pBS32-Encoded Sigma Factor in Bacillus subtilis

“…pBS32 is a large, 84-kb, low-copy-number plasmid that has a separate replication initiation protein and a high-fidelity plasmid partitioning system (6, 8–10). Moreover, pBS32 has been shown to encode an inhibitor of competence for DNA uptake (ComI) (7) and an inhibitor of biofilm formation (RapP) that regulates cell physiology (11–13). In addition, approximately one-third of the pBS32 sequence encodes a cryptic prophage-like element, and cell death is triggered in a pBS32-dependent manner following treatment with the DNA-damaging agent mitomycin C (MMC) (7, 14–17).…”

Multiple and Overlapping Functions of Quorum Sensing Proteins for Cell Specialization in Bacillus Species

“…subtilis 168 has 11 QS-Rap proteins paralogs encoded in the chromosome (RapA through RapK) (reviewed in reference 16). Other Rap proteins encoded in plasmids (RapP, Rap40, Rap50, Rap60, and LS20) have been described in different strains (29)(30)(31)(32). These Rap proteins modulate at least three signal transduction pathways, sporulation, integrative and conjugative transfer elements (ICEs), and competence (16,(29)(30)(31) (Fig.…”

“…However, some efforts have been recently made to assess the impact of proteins that target the Spo0A phosphorelay in more realistic, ecologically relevant settings, in contrast to classic, unrealistic experiments in liquid medium. For example, coinoculation experiments using B. subtilis strains showed that RapP is involved in maintaining a low production of surfactin to avoid subsequent cheating in swarms of B. subtilis (30). Also, in B. thuringiensis, the loss of NprR causes only slight delays in sporulation initiation in liquid medium (23), but this protein is essential for necrotrophism and sporulation in insect hosts (88); therefore, this QS system may provide a fitness advantage to the bacterial population in nature.…”

Cheaters shape the evolution of phenotypic heterogeneity in Bacillus subtilis biofilms

“…Recent studies showed that in well-mixed environment, cooperators adapt to cheats by reducing cooperation [ 14 , 15 , 33 ]. Such reduction could be achieved by various strategies, for instance decrease in motility [ 15 ], downregulation or minimal production in public goods [ 14 , 15 , 33 ], upregulation of other alternative public goods [ 14 ], or bi-stable expression in virulence gene [ 2 ]. Interestingly, populations of cooperators often exhibit phenotypic heterogeneity at the single-cell level [ 34 , 35 ].…”