Poly-beta-hydroxybutyrate membrane structure and its relationship to genetic transformability in Escherichia coli

Abstract

The effects of competence-inducing treatments on the composition and organization of membrane lipids in Escherichia coli K-12, DH1, DH5, HB101, and RR1 were investigated for two widely used protocols in which transformability is developed at low temperatures in Ca2+ buffers. At stages during each procedure, the lipid compositions of the cells were determined, and the thermotropic lipid phase transitions were observed in whole cell culture by fluorescence assay with the hydrophobic probe N-phenyl-1-naphthylamine. Competence was evaluated by determining transformation efficiencies with plasmid pBR322 DNA. The competence-inducing procedures effected only slight changes in phospholipid compositions which did not correlate with transformability. However, the induction of competence was coincident with de novo synthesis and incorporation of poly-beta-hydroxybutyrate into the cytoplasmic membranes and with the appearance of a sharp lipid phase transition above physiological temperatures. Transformation efficiencies correlated with poly-beta-hydroxybutyrate concentrations and with the intensity of the new phase transition. Transformability, poly-beta-hydroxybutyrate synthesis and the new phase transition were not significantly affected by inhibition of protein synthesis with chloramphenicol or inhibition of respiration or ATP synthesis with azide, cyanide, arsenate, or 2,4-dinitrophenol; however, when poly-beta-hydroxybutyrate synthesis was inhibited with acetaldehyde, the new phase transition was not observed, and competence failed to develop. These studies suggest that genetic transformability in E. coli may be physiologically regulated.