When less is more: cell size reduction as a metabolic lifeline in Mycoplasma gallisepticum.

INTRODUCTION: How living cells regulate their function and adapt to stress remains a fundamental question in cell biology. In bacteria, stress responses are classically described at the genomic and transcriptomic levels; however, this paradigm does not adequately explain adaptation in mycoplasmas, which are widely regarded as a model of a minimal cell.

METHODS: This study investigated stress adaptation in mycoplasmas by analyzing cellular volume and morphology changes by SEM, DLS, and EPR. Membrane lipid composition was analyzed by mass spectrometry. Intracellular ATP levels were measured using a luciferase‑based assay. Vesicles were isolated by ultracentrifugation and characterized by proteomics, enzyme activity assays, and ATP measurements. Glycolytic flux was assessed in vitro using recombinant enzymes and liposome encapsulation.

RESULTS: Stress adaptation in this minimal cell is primarily achieved through a reduction in cellular volume, mediated by the release of the attachment organelle ("tip") in the form of vesicles. This process triggers metabolic reorganization within the cell and results in the accumulation of ATP. The metabolic adaptation involves changes in the stoichiometric balance of glycolytic enzymes and alterations in local metabolite concentrations under conditions of reduced cell volume, both of which directly influence glycolytic flux. Concurrently, the released vesicles contain VlhA, lipoproteins, adhesins, hydrogen-peroxide-secreting factors, and exhibit peptidase activity.

DISCUSSION: These findings reveal a novel regulatory mechanism in a minimal cell, where physical volume reduction and biochemical adjustments may be related to an energy-efficient stress response. The dual role of vesicle formation-in cellular remodeling and pathogenesis-deepens our understanding of mycoplasma biology and offers insights for synthetic cell design.