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Human microbiomes are composed of complex and dense bacterial consortia. In these environments, bacteria are able to react quickly to change by coordinating their gene expression at the population level via small signaling molecules. In Gram-positive bacteria, cell-cell communication is mostly mediated by peptides that are released into the extracellular environment. Cell-cell communication based on these peptides is especially widespread in the group Firmicutes, in which they regulate a wide array of biological processes, including functions related to host-microbe interactions. Among the different agents of communication, the RRNPP family of cytoplasmic transcriptional regulators, together with their cognate re-internalized signaling peptides, represents a group of emerging importance. RRNPP members that have been studied so far are found mainly in species of bacilli, streptococci, and enterococci. These bacteria are characterized as both human commensal and pathogenic, and share different niches in the human body with other microorganisms. The goal of this mini-review is to present the current state of research on the biological relevance of RRNPP mechanisms in the context of the host, highlighting their specific roles in commensalism or virulence. [ABSTRACT FROM AUTHOR]

Within Gram-positive bacteria, the expression of target genes is controlled at the population level via signaling peptides, also known as pheromones. Pheromones control a wide range of functions, including competence, virulence, and others that remain unknown. Until now, their role in bacterial gene regulation has probably been underestimated; indeed, bacteria are able to produce, by ribosomal synthesis or surface protein degradation, an extraordinary variety of peptides which are released outside bacteria and among which, some are pheromones that mediate cell-to-cell communication. The review aims at giving an updated overview of these peptide-dependant communication pathways. More specifically, it follows the whole peptide circuit from the peptide production and secretion in the extracellular medium to its interaction with sensors at bacterial surface or re-import into the bacteria where it plays its regulation role. In recent years, as we have accumulated more knowledge about these systems, it has become apparent that they are more complex than they first appeared. For this reason, more research on peptide-dependant pathways is needed to develop new strategies for controlling functions of interest in Gram-positive bacteria. In particular, such research could lead to alternatives to the use of antibiotics against pathogenic bacteria. In perspective, the review identifies new research questions that emerge in this field and that have to be addressed. [ABSTRACT FROM PUBLISHER]

We described a quorum-sensing mechanism in the streptococci genus involving a short hydrophobic peptide (SHP), which acts as a pheromone, and a transcriptional regulator belonging to the Rgg family. The shp/rgg genes, found in nearly all streptococcal genomes and in several copies in some, have been classified into three groups. We used a genetic approach to evaluate the functionality of the SHP/Rgg quorum-sensing mechanism, encoded by three selected shp/rgg loci, in pathogenic and non-pathogenic streptococci. We characterized the mature form of each SHP pheromone by mass-spectrometry. We produced synthetic peptides corresponding to these mature forms, and used them to study functional complementation and cross-talk between these different SHP/Rgg systems. We demonstrate that a SHP pheromone of one system can influence the activity of a different system. Interestingly, this does not seem to be dependent on the SHP/Rgg group and cross-talk between pathogenic and non-pathogenic streptococci is observed. [ABSTRACT FROM AUTHOR]