1887

Abstract

Summary: The ability of a bacterial pathogen associated with dental caries, to tolerate rapid drops in plaque pH (acidurance), is considered an important virulence factor. To study this trait, Tn mutants of strain JH1005 which display acid sensitivity have been isolated and partially characterized. In this paper, the characterization of one of these mutants, AS17, is reported. Preliminary sequence analysis revealed that the transposon insertion in AS17 occurred in the intergenic region of a two-gene locus which has been named for cretion and acid lerance. This locus displays a high degree of homology to the operon of The locus was cloned by complementation of a conditional mutant with an genomic library. Sequencing of the complementing clone identified the intact and genes as well as a partial ORF with homology to the gene of which encodes the binding protein of the ProU/OpuA osmoregulated glycine betaine transport system. RNA dot blot experiments indicated steady-state levels of mRNA in the mutant that were approximately eightfold lower compared to parental levels. This suggests a partial polar effect of the ::Tn mutation on expression. Upon acid shock (pH 5), wild-type mRNA levels were found to increase approximately four- to eightfold compared to unstressed (pH 7·5) levels. Mutant levels remained unaltered under the same conditions. Experiments designed to investigate the origins of the acid-sensitivity of the mutant revealed a lack of an acid-adaptive/tolerance response. Assays of proton-extruding ATPase (H/ATPase) specific activity measured with purified membranes derived from acid-shocked AS17 showed twofold lower levels compared to the parent strain. Also, AS17 was found to be unable to ferment sorbitol although it was able to grow in glucose and a variety of other sugar substrates. These findings suggest that Ffh may be involved in the maintenance of a functional membrane protein composition during adaptation of to changing environmental conditions.

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/content/journal/micro/10.1099/13500872-145-2-357
1999-02-01
2019-10-15
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