Seduk, F. | bioRxiv Science

bioRxiv2026

Cardiolipin constrains lipid unsaturation during anaerobic adaptation in Escherichia coli

Membrane lipids play a crucial role in cellular adaptation; though their specific functions in bacterial adaptation to oxygen limitation are not yet fully elucidated. Cardiolipin (CL), a signature phospholipid in energy-transducing membranes and a key organizer of mitochondrial respiration, has an unclear role in bacterial anaerobic physiology. Here, genetics, quantitative lipidomics and proteomics, enzymology, and fluorescence imaging were combined to explore how CL facilitates hypoxia adaptation in Escherichia coli. ClsA emerged as the predominant CL synthase under anaerobic conditions, and CL deficiency selectively impaired nitrate-dependent growth, while fermentation and fumarate respiration remained largely unaffected. CL depletion triggered extensive lipidome rewiring during the aerobic-to-anaerobic transition, including increased levels of phosphatidylglycerol, phosphatidic acid, and diacylglycerol, along with a broad enrichment of more unsaturated lipid species. In parallel, proteome remodeling linked CL loss to reduced abundance of proteins involved in anoxic respiration and nitrosative stress management, alongside the induction of membrane stress responses. Interestingly, CL deficiency did not markedly affect cell morphology, nor the spatial distribution or stability of respiratory complexes. This suggests a specialized role in optimizing membrane protein function rather than providing generic structural support. Wild-type lipidome profiling further showed that anaerobiosis induces a shift of lipid species toward higher unsaturation, with only modest class-level changes. Collectively, these results connect lipid remodeling to functional outcomes in vivo, offering mechanistic insights into how bacteria adapt their membranes to maintain energy conservation in fluctuating environments.

microbiology↗

bioRxiv2023

Spatio-temporal dynamics of the proton motive force on single bacterial cells

Electrochemical gradients established across biological membranes are fundamental in the bioenergetics of all forms of life. In bacteria, the proton motive force (PMF), the electrochemical potential associated to protons, powers an impressive array of fundamental processes, from ATP production to motility. While far from equilibrium, it has classically been considered homeostatic in time and space. Yet, recent experiments have revealed rich temporal dynamics at the single cell level and functional spatial dynamics at the scale of multicellular communities. Lateral segregation of supramolecular respiratory complexes begs the question of whether spatial heterogeneity of the PMF exists even at the single cell level. By using a light-activated proton pump as a spatially and temporally modulatable source, and the bacterial flagellar motor as a local electro-mechanical gauge, we both perturb and probe the PMF on single cells. Using global perturbations, we resolve temporal dynamics on the ms time scale and observe an asymmetrical capacitive response of the cell. Using localized perturbations, we find that the PMF is rapidly homogenized along the entire cell, faster than proton diffusion can allow. Instead, the electrical response can be explained in terms of electrotonic potential spread, as found in passive neurons and described by cable theory. This implies a global coupling between PMF sources and consumers in the bacterial membrane, excluding a sustained spatial heterogeneity while allowing for fast temporal dynamics. SignificanceStoring energy in the form of a proton gradient across a membrane is a fundamental feature of living systems. In mitochondria, spatial compartmentalization separates electrically distinct regions. In bacteria, it is unclear how this energy reservoir, the proton motive force, behaves at the single cell level: can it be heterogeneous in space as in mitochondria? How fast can it change in time? Using a light-driven proton pump and the flagellar motor as a local electro-mechanical gauge, we find that the bacterial proton motive force can change in a few tens of milliseconds, and that it is instantaneously homogenized along the membrane. This electrophysiological response is surprisingly similar to electrotonic voltage spread in passive neurons.

biophysics↗