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

Abstract

In bacterial populations, quorum sensing (QS) systems participate in the regulation of specialization processes and regulate collective behaviors that mediate interactions and allow survival of the species. In Gram-positive bacteria, QS systems of the RRNPP family (Rgg, Rap, NprR, PlcR, and PrgX) consist of intracellular receptors and their cognate signaling peptides. Two of these receptors, Rap and NprR, have regained attention in Bacillus subtilis and the Bacillus cereus group. Some Rap proteins, such as RapH and Rap60, are multifunctional and/or redundant in function, linking the specialization processes of sporulation and competence, as well as global expression changes in the transition phase in B. subtilis. NprR, an evolutionary intermediate between Rap and RRNPP transcriptional activators, is a bifunctional regulator that modulates sporulation initiation and activates nutrient scavenging genes. In this review, we discuss how these receptors switch between functions and connect distinct signaling pathways. Based on structural evidence, we propose that RapH and Rap60 should be considered moonlighting proteins. Additionally, we analyze an evolutionary and ecological perspective to understand the multifunctionality and functional redundancy of these regulators in both Bacillus spp. and non-Bacillus Firmicutes. Understanding the mechanistic, structural, ecological, and evolutionary basis for the multifunctionality and redundancy of these QS systems is a key step for achieving the development of innovative technologies for health and agriculture.

A native conjugative plasmid confers potential selective advantages to plant growth-promoting Bacillus velezensis strain GH1-13

“…During the exponential phase of cell growth, expression of comA that is transcriptionally regulated by a distinct Rap-Phr system 27 was not detected in any variant of strains GH1-13 an FZB42. Overall, these expression patterns appear to play a role in the QS-regulated expression of rap and phr genes involved in multiple and overlapping directions for cell specialization 28 . In the genome of strain GH-13, the PhrF2 sequence was not previously found owing to the usage of the alternative translation initiation site in the rapF2 cassette and a lack of similarity between the propeptide sequence and any known sequences in gram-positive bacteria 29 .…”

Peptidomimetics as Potential Anti-Virulence Drugs Against Resistant Bacterial Pathogens

“…In this system, AIP is translated, exported, and internalized again for target interaction ( Perez-Pascual et al, 2016 ). It is also involved in intra- and interspecific communications ( Verdugo-Fuentes et al, 2020 ). Unlike the pathway of the two-component system, previously mentioned, this system imports the respective AIP to target intracellular factors ( Perez-Pascual et al, 2016 ; McBrayer et al, 2020 ).…”

Pyrones Identified as LuxR Signal Molecules in Photorhabdus and Their Synthetic Analogues Can Alter Multicellular Phenotypic Behavior of Bacillus atropheaus

“…QS plays a role in biofilm development and swarming motility in B. subtilis, 33,45,46 with AI-2 signaling recently reported eliciting a biofilm-dependent response through the LuxS receptor under specific environmental conditions. 47 A LuxR-type receptor−ligand interaction, such as that described for the pyrones in Photorhabdus, would equally be complex and likely multifaceted.…”