Cellular incorporation of poly-beta-hydroxybutyrate into plasma membranes of Escherichia coli and Azotobacter vinelandii alters native membrane structure.

Under growth-limiting conditions or conditions which mediate genetic transformation, Escherichia coli and Azotobacter vinelandii incorporate poly-beta-hydroxybutyrate into their plasma membranes. Genetic transformation competence of both bacteria increased in proportion to the concentration of membrane poly-beta-hydroxybutyrate. The effects of this lipid polymer on membrane structure were investigated by freeze-fracture electron microscopy. Before poly-beta-hydroxybutyrate incorporation, freeze-fracture revealed a typical mosaic of particles and pits on both concave and convex surfaces of the plasma membrane. As the cells incorporated the lipid polymer into the membrane, transformability developed and small semiregular plaques which possessed shallow particles were seen. These plaques grew in size and frequency as the membrane poly-beta-hydroxybutyrate concentrations and transformability increased.