Biology subjects

Delaby, M.

Publications and source records attributed to Delaby, M..

3 recordsLinked to original sources

bioRxiv2026

MreB is dispensable for viability but critical for rod shape, motility and biofilm fitness in Pseudomonas aeruginosa

Despite growing interest in the MreBCD morphogenetic complex as a potential antimicrobial target, its function in Pseudomonas aeruginosa remains poorly understood. While previous studies using the MreB inhibitor A22 have established its role in cell shape maintenance and pilus regulation, the impact of mreB deletion has not been comprehensively investigated. Using genetic and microscopy-based approaches, we show that deletion of mreB is viable in P. aeruginosa, but results in spherical cells that lose all forms of motility despite retaining flagella. Importantly, we uncover a previously overlooked polar effect of the in-frame mreB deletion on the downstream mreCD genes and show, using CRISPRi-mediated silencing, that mreCD expression is essential for viability.{Delta} mreB mutants also display increased sensitivity to {beta}-lactam antibiotics and enhanced initial surface attachment, yet form more compact biofilms with reduced dispersal. In mixed-culture biofilms, spherical{Delta} mreB cells are outcompeted by rod-shaped wild-type cells and remain confined to the biofilm base. The identification of natural P. aeruginosa isolates carrying truncated mreB alleles further indicates that loss of MreB function can be tolerated in natural populations. Together, our findings reveal important contributions of the MreBCD system to viability, morphogenesis, motility and biofilm development in P. aeruginosa, providing new insights into bacterial adaptation and informing the development of targeted antimicrobial strategies.

microbiology↗

bioRxiv2024

Phenotypic plasticity in bacterial elongation among closely related species

Cell elongation is a fundamental component of the bacterial cell cycle and has been studied over many decades, in part owing to its mechanisms being a target of numerous antibiotic classes. While several distinct modes of cell elongation have been described, these studies have largely relied on a handful of model bacterial species. Therefore, we have a limited view of the diversity of cell elongation approaches that are employed by bacteria, and how these vary in response to evolutionary and environmental influences. Here, by employing fluorescent D-amino acids (FDAAs) to track the spatiotemporal dynamics of elongation, we reveal previously unsuspected diversity of elongation modes among closely related species of the Caulobacteraceae, with species-specific combinations of dispersed, midcell and polar elongation that can be either unidirectional or bidirectional. Using genetic, cell biology, and phylogenetic approaches, we demonstrate that evolution of unidirectional-midcell elongation is accompanied by changes in the localization pattern of the peptidoglycan synthase PBP2 and infer that elongation complexes display a high degree of phenotypic plasticity, both among the Caulobacteraceae and more widely among the Alphaproteobacteria. Demonstration that even closely related bacterial species employ highly distinct mechanisms of cell elongation reshapes our understanding of the evolution and regulation of bacterial cell growth, with broad implications for bacterial morphology, adaptation, and antibiotic resistance.

microbiology↗

bioRxiv2019

Bacterial cell cycle and growth phase switch by the essential transcriptional regulator CtrA

Many bacteria acquire dissemination and virulence traits in G1-phase. CtrA, an essential and conserved cell cycle transcriptional regulator identified in the dimorphic alpha-proteobacterium Caulobacter crescentus, first activates promoters in late S-phase and then mysteriously switches to different target promoters in G1-phase. We uncovered a highly conserved determinant in the DNA-binding domain (DBD) of CtrA uncoupling this promoter switch. We also show that it reprograms CtrA occupancy in stationary cells inducing a (p)ppGpp alarmone signal perceived by the RNA polymerase beta subunit. A simple side chain modification in a critical residue within the core DBD imposes opposing developmental phenotypes and transcriptional activities of CtrA. A naturally occurring polymorphism in the rickettsial DBD resembles a mutation that drives CtrA towards activation of the dispersal (G1-phase) program in Caulobacter. Hence, we propose that this determinant dictates promoter reprogramming during the growth transition of obligate intracellular rickettsia differentiating from replicative cells into dispersal cells.

microbiology↗