Environmental modulation of lipopolysaccharide chain length alters the sensitivity of Escherichia coli to the neutrophil bactericidal/permeability-increasing protein.

We have shown previously that the sensitivity of Escherichia coli to the neutrophil bactericidal/permeability-increasing protein (BPI) depends mainly on the polysaccharide chain length of outer membrane lipopolysaccharides (LPS) (J. Weiss, S. Beckerdite-Quagliata, and P. Elsbach, J. Clin. Invest. 65:619-628, 1980). Thus, rough strains of E. coli producing only short-chain LPS are more sensitive to BPI than smooth strains that produce LPS with varied chain lengths. We now show that changes in the bacterial growth environment can modify BPI sensitivity of smooth E. coli as much as 30-fold depending on the bacterial strain and the growth conditions examined. Changes in BPI sensitivity paralleled differences in binding affinity of E. coli for BPI and closely correlated with changes in the chain length of LPS produced under different growth conditions, as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. No concomitent changes in either the number of LPS molecules per cell or the bacterial protein profile were detected. Rough strains showed little or no growth-dependent variation in BPI sensitivity, further indicating that subtle alterations in bacterial constituents other than LPS do not significantly affect bacterial sensitivity to BPI. Thus, the BPI sensitivity of E. coli can be modulated not only by the genotypic conversion of the LPS phenotype, but also by environmental effects on LPS-polysaccharide formation in wild-type strains.