Characterisation of intracellular gas bubbles in Saccharomyces

The yeast fermentation process is well established. However, until recently no sign of intracellular gas bubbles had been reported. A paradigm shift emanated when intracellular gas bubbles were discover using various microscopy techniques thereby resolving the missing link between CO2 production and eventual release from the cells. The lack of membranes around the gas bubbles served as a distinguishing feature of the bubbles. However, there had been other non-enveloped structure that had been reported as either lipid droplets or vacuole fragments. This study, using organelle-specific fluorescent probes, shows that intracellular gas bubbles, lipid droplets and vacuole fragments are separate inclusions that can coexist in the cell. Considering that intracellular gas bubbles compress and deform organelles, coupled to the fact that yeast cells have an internal pressure of 2.1 MPa and that pressurised CO2 has been reported to have adverse effects on microorganisms warranted an investigation into the effect of intracellular gas bubbles on cell function. This study concludes that the formation of intracellular gas bubbles did not have a negative effect on mitochondrial activity. The observation of fermenting S. pastorianus cells (more gas bubbles) having lower lipid content than respiring cells (few gas bubbles) indicates that the gas bubble formation plays a role in controlling the buoyant cell density of fermenting in this strain. This suggests that the influence of bubble formation may be limited and strain dependent.