Fecha de publicación: -- Fuente: PubMed "swarm" Microbiol Res. 2026 Nov 3;315:128812. doi: 10.1016/j.micres.2026.128812. Online ahead of print.ABSTRACTBiofilm are spatially structured microbial communities where environmental gradients impose stress that drive bacterial adaptation. In this study, we show that the RelA-mediated stringent response orchestrates pleomorphism and stress resilience in Bacillus subtilis biofilm at acidic pH. Acidic conditions increased membrane fluidity and induced depolarization, which led to the upregulation of relA and the repression of cytoskeletal genes, thereby reducing cell size. Supplementation with Mg2+, an essential cofactor for RelA, reduced cell size, suppressed dispersal pathways, and stimulated extracellular matrix production, ultimately enhancing biofilm integrity. In contrast, ΔrelA mutants failed to mount a stringent response and displayed aberrant morphology, reduced swarming motility and impaired pellicle formation. Moreover, this mutation led to a defect in adaptation to acid stress and was correlated with altered expression of the SigD regulon. These findings establish the RelA-mediated stringent response as the central switch coupling acidic pH sensing to morphological plasticity, membrane remodelling, and collective stress tolerance. By coordinating pleomorphic transitions with biofilm stabilization, RelA enables bacterial populations to withstand hostile microenvironments while maintaining structural cohesion. This study shows that the stringent response is an important factor in bacterial survival and identifies RelA as a key regulator of biofilm pleomorphism and stress tolerance, which could be targeted to interfere with biofilm persistence in clinical, industrial and ecological contexts.PMID:42994042 | DOI:10.1016/j.micres.2026.128812