Weibel, D. B. | bioRxiv Science

bioRxiv2019

Rcs phosphorelay activation in cardiolipin-deficient Escherichia coli reduces biofilm formation

Biofilm formation is a complex process that requires a number of transcriptional, proteomic, and physiological changes to enable bacterial survival. The lipid membrane presents a barrier to communication between the machinery within bacteria and the physical and chemical features of their extracellular environment, and yet little is known about how the membrane influences biofilm development. We found that depleting the anionic phospholipid cardiolipin reduces biofilm formation in Escherichia coli cells by as much as 50%. The absence of cardiolipin activates the Rcs envelope stress response, which represses production of flagella, disrupts initial biofilm attachment, and reduces biofilm growth. We demonstrate that a reduction in the concentration of cardiolipin impairs translocation of proteins across the inner membrane, which we hypothesize activates the Rcs pathway through the outer membrane lipoprotein RcsF. Our study demonstrates a molecular connection between the composition of membrane phospholipids and biofilm formation in E. coli and suggests that altering lipid biosynthesis may be a viable approach for altering biofilm formation and possibly other multicellular phenotypes related to bacterial adaptation and survival.\n\nImportanceThere is a growing interest in the role of lipid membrane composition in the physiology and adaptation of bacteria. We demonstrate that a reduction in the anionic phospholipid cardiolipin impairs biofilm formation in Escherichia coli cells. Depleting cardiolipin reduced protein translocation across the inner membrane and activated the Rcs envelope stress response. Consequently, cardiolipin depletion produced cells lacking assembled flagella, which impacted their ability to attach to surfaces and seed the earliest stage in biofilm formation. This study provides empirical evidence for the role of anionic phospholipid homeostasis in protein translocation and its effect on biofilm development, and highlights modulation of the membrane composition as a potential method of altering bacterial phenotypes related to adaptation and survival.

microbiology↗

bioRxiv2018

Bacterial swarming reduces Proteus mirabilis and Vibrio parahaemolyticus cell stiffness and increases β-lactam susceptibility

Swarmer cells of the gram-negative pathogenic bacteria Proteus mirabilis and Vibrio parahaemolyticus become long (>10-100 m) and multinucleate during their growth and motility on polymer surfaces. We demonstrate increasing cell length is accompanied by a large increase in flexibility. Using a microfluidic assay to measure single-cell mechanics, we identified large differences in swarmer cell stiffness of (bending rigidity of P. mirabilis, 9.6 x 10-22 N m2; V. parahaemolyticus, 9.7 x 10-23 N m2) compared to vegetative cells (1.4 x 10-20 N m2 and 3.2 x 10-22 N m2, respectively). The reduction in bending rigidity (~3-15 fold) was accompanied by a decrease in the average polysaccharide strand length of the peptidoglycan layer of the cell wall from 28-30 to 19-22 disaccharides. Atomic force microscopy revealed a reduction in P. mirabilis peptidoglycan thickness from 1.5 nm (vegetative) to 1.0 nm (swarmer) and electron cryotomography indicated changes in swarmer cell wall morphology. P. mirabilis and V. parahaemolyticus swarmer cells became increasingly sensitive to osmotic pressure and susceptible to cell wall-modifying antibiotics (compared to vegetative cells)--they were ~30% more likely to die after 3 h of treatment with minimum inhibitory concentrations of the {beta}-lactams cephalexin and penicillin G. The adaptive cost of swarming is offset by the increase in cell susceptibility to physical and chemical changes in their environment, thereby suggesting the development of new chemotherapies for bacteria that leverage swarming for colonization of hosts and survival. ImportanceProteus mirabilis and Vibrio parahaemolyticus are bacteria that infect humans. To adapt to environmental changes, these bacteria alter their cell morphology and move collectively to access new sources of nutrients in a process referred to as swarming. We found that a change in the composition and thickness of the peptidoglycan layer of the cell wall makes swarmer cells of P. mirabilis and V. parahaemolyticus more flexible (i.e., reduced cell stiffness) and increases their sensitivity to osmotic pressure and cell-wall targeting antibiotics (e.g., {beta}-lactams). These results highlight the importance of assessing the extracellular environment in determining antibiotic doses and the use of {beta}-lactams antibiotics for treating infections caused by swarmer cells of P. mirabilis and V. parahaemolyticus.

microbiology↗