Abstract
Electron microscopy previously revealed that Gluconobacter oxydans differentiates by forming quantities of intracytoplasmic membranes at the end of exponential growth. It was also shown that the formation of these membranes appears concurrently with an increased rate of polyol oxidation. In the present study, exponential-phase cells devoid of intracytoplasmic membranes were harvested and the quantity of free lipid was determined. This quantity was compared with that extracted from cells harvested 4 and 16 h into the stationary phase that contained intracytoplasmic membranes. Cells harvested 4 and 16 h into the stationary phase contained 58 and 43% more free lipid per 100 mg of cell weight than found in undifferentiated exponential-phase cells. These same cultures were used to compare the quantity of lipid extracted per cell. This analysis revealed 89 and 142% more lipid per cell in 4 and 16 h stationary-phase cells. Further study demonstrated that cells increased in length and decreased in density with time after they entered the stationary phase. We estimated, however, that intracytoplasmic membrane development in G. oxydans is accompanied by a 57 to 62% increase in free-lipid that cannot be attributed to a change in cell size. These results suggest that the traditional expression of extracted lipid per milligram of cellular dry weight should not be used for comparative purposes during differentiation in gram-negative bacteria, unless it is first established that both cell size and cell density remain constant throughout differentiation.