BERGE, M. | Search bioRxiv

bioRxiv2026

The broad-spectrum RumC1 bacteriocin targets a transient peptidoglycan intermediate of the nascent cell wall

RumC1 is a structurally unique bacteriocin with broad-spectrum efficacy, including against multidrug-resistant pathogens, yet acting by an undefined mechanism. By integrating genetics, biochemistry, computational modeling and single-cell fluorescence microscopy, we demonstrate that RumC1 is a distinct cell-wall-targeting toxin. First, all RumC1-resistant mutants isolated through a high-rate, genome-wide mutagenic screening exhibited specific impairments in peptidoglycan homeostasis regulation, pinpointing this pathway as critical for RumC1 activity. Second, RumC1 selectively accumulates within neosynthesized peptidoglycan, leading to cell growth arrest and death in a dose-dependent manner. Third, we characterize the RumIc1 immunity protein of the RumC1 biosynthetic cluster as a peptidase acting at the cell surface to protect the cells by trimming the stem peptide crucial for cell-wall assembly. As such, RumIc1 provides cross-protection against vancomycin, while RumC1 is demonstrated to act differently from this glycopeptide antibiotic. Collectively, these findings establish RumC1 as a toxin targeting a key peptidoglycan intermediate of cell wall maturation.

microbiology↗

bioRxiv2025

A toxin/antitoxin system targeting the replication sliding-clamp induces competence in Streptococcus pneumoniae.

Streptococcus pneumoniae is a pathogenic bacterium capable of entering a cellular differentiation state, called competence, which enables it to acquire new genetic functions by natural transformation, as well as physiological functions such as tolerance to a number of antibiotics. The transition to this state is regulated by various environmental or intracellular signals that converge on the comCDE operon, which groups together the competence initiation genes. A fraction of activated cells is sufficient to propagate competence to the whole population via the product of the comC gene, the competence stimulating peptide (CSP). Remarkably, depletion of the essential ClpX/ ClpP AAA+ protease has been shown to induce the comCDE operon. Here we demonstrate that the ClpX-dependent induction of competence relies on the Spr1630 toxin (RipA), part of a Rosmer toxin-antitoxin system. We show that this toxin generates replicative stress by acting on the sliding clamp of replication, inducing transcription of the comCDE operon. Bacteria that produce RipA appear to lose their viability but remain metabolically active and able to produce CSP, thereby transferring competence to viable neighbouring cells. Authors summaryThe environment in which bacteria live puts them under a great deal of stress, forcing them to adapt constantly, either temporarily or permanently. Streptococcus pneumoniae, a pathogenic bacterium implicated in various pathologies such as otitis, meningitis and pneumonia, is also subject to stress, whether from its host, antibiotic treatments or the microbiota in which it lives. In response to this, S. pneumoniae is able to switch to a differentiated state called competence. This allows it to acquire new genetic characteristics through natural transformation, but also to better tolerate stresses such as antibiotics pressure. The underlying signals and signaling pathways of this phenotypic switch remain poorly characterized. In this study, we identified a novel toxin-antitoxin system that, when activated, causes a subset of the population to self-sacrifice by disrupting its own DNA replication. This self-induced arrest serves as a signal that promotes the transition to competence in neighboring cells, thereby improving the capacity for adaptation at the populational level.

microbiology↗