Iron-dependent production of a heat-modifiable, 23,000-Mr outer membrane protein in Paracoccus denitrificans

Role of the cell envelope in bacterial adaptation to growth in vivo in infections

To establish an infection, a pathogenic bacterium must adapt to growth in the hostile environment encountered in vivo in host tissues. The cell envelope plays a crucial role in this adaptive process, since it is involved in promoting adhesion to and colonisation of host tissues, in the acquisition of essential nutrients and in conferring resistance to host defences and to antibiotics. Its properties are ultimately determined by the information stored within the genome, which also contains the potential to respond to environmental change. The macromolecular structure and function of the cell envelope are largely determined by the growth environment and, in particular, specific nutrient limitation, growth rate, growth temperature and replication in suspension or within a surface-associated biofilm. Bacteria growing in vivo will manufacture envelopes characteristic of that environment and which will differ markedly in physiology, biochemistry and immunogenicity from those of cells grown in a standard laboratory medium. In vivo, the ability to withhold iron is an important component of the host's defence and iron deprivation has a pronounced effect on the metabolism and cell envelope properties of pathogenic bacteria. The phenotypic plasticity of the bacterial cell surface plays an important role in determining susceptibility to host defences and antibiotics and has important implications for the design and evaluation of new therapeutic strategies for the treatment and prevention of bacterial infections.

Increased outer membrane ornithine-containing lipid and lysozyme penetrability of Paracoccus denitrificans grown in a complex medium deficient in divalent cations

Paracoccus denitrificans grown in a complex medium was highly susceptible to lysozyme, in contrast to cells grown in a complex medium supplemented with Mg2+ and Ca2+ or in a succinate-salts medium. The complex medium was deficient in divalent cations needed for optimum outer membrane stability. The major change in molecular compositions of outer membranes isolated from cells grown under the different conditions was a higher ratio of ornithine-containing lipid to phospholipid in complex-medium-grown cells (0.63) than in cells grown in complex medium with Mg2+ and Ca2+ (0.22) or in succinate-salts medium (0.14). We suggest that the dipolarionic ornithine-containing lipid is less dependent than acidic phospholipids on divalent cations for its incorporation into the outer membrane.