| Summary: | 碩士 === 長庚大學 === 基礎醫學研究所 === 96 === Streptococcus parasanguinis is one of the primary colonizers of tooth surface and an opportunistic cause of subacute endocarditis. Fimbriae-associated protein 1 (Fap1) is the structural subunit of S. parasanguinis FW213 long fimbriae, and glycosylation of Fap1 is required for adherence and biofilm formation in FW213. Genes encoding Fap1 and proteins for Fap1 glycosylation are located in a pathogenicity island. Previous studies revealed that the amount of fimbriation varies along the development of growth stages, but the mechanism governs the differential expression is not yet defined. In this study, a recombinant fap1 promoter (pfap1)-cat fusion strain was constructed and grown in continuous chemostat under various conditions to evaluate the impact of growth parameters on pfap1 expression. A higher level of pfap1 expression and genes involved in glycosylation of Fap1 was observed in cells grown at acidic pH under glucose excess condition. The up-regulation by acidic pH was not related to growth phase, as a decline in pfap1 activity was detected along with the development of growth in a batch-grown, pH 7.5 culture, thus the pH, carbohydrate concentration and growth phase affect the synthesis of fimbriae. The up regulation of fimbriae synthesis also agrees with the optimal biofilm formation under such growth conditions. Furthermore, the amount of secreted-Fap1 was higher under natural pH condition, regardless the glucose concentration, suggesting S. parasanguinis could promote its survival by titrating antibody specific for Fap1 in the circulatory system. By using a sortase A (srtA)-deficient mutant, it was found that the anchoring of Fap1 was catalyzed by SrtA. Further analysis indicated that the expression of srtA was down-regulated at neutral pH, thus it is likely that SrtA regulated directly the amount of secreted Fap1 at various pH. Thus, the differential regualtion of fimbria synthesis will ensure a successful initial adherence and subsequent biofilm formation. Such regulation will allow for the optimal binding and pathogenic capacity of FW213.
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