1887

Abstract

Capsule depolymerase (CapD) is a -glutamyl transpeptidase and a product of the capsule biosynthesis operon. In this study, we examined the effect of modulating expression on capsule phenotype, interaction with phagocytic cells and virulence in guinea pigs. Transcriptional fusions of were made to the genes encoding heat-shock protein 60 () and elongation factor Tu (), and to a capsule biosynthesis gene. Translation signals were altered to improve expression of , including replacing the putative ribosome-binding site with a consensus sequence and the TTG start codon with ATG. CapD was not detected by immunoblotting in lysates from wild-type Ames but was detected in strains engineered with a consensus ribosome-binding site for . Strains overexpressing at amounts detected by immunoblotting were found to have less surface-associated capsule and released primarily lower-molecular-mass capsule into culture supernatants. Overexpression of increased susceptibility to neutrophil phagocytic killing and adherence to macrophages and resulted in reduced fitness in a guinea pig model of infection. These data suggest that may have evolved weak expression resulting in optimized capsule-mediated virulence.

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2010-05-01
2020-01-20
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