| Summary: | 碩士 === 長庚大學 === 生物醫學研究所 === 105 === Streptococcus salivarius is the major ureolytic microbe in the human
mouth, and the expression of urease in strain 57.I is upregulated at acidic
growth pH and under glucose excess. Earlier studies indicate that the
enzyme II (EIIMan) of the phosphoenolpyruvate: mannose
phosphotransferase system (Man-PTS), the enzyme I of PTS and CcpA all
participate in urease regulation. This study revealed that CcpA repressed
manL expression, gene encoding the light form of EIIMan in cells grown in
galactose, suggesting that CcpA regulates urease expression, at least in part,
by controlling manL expression. By using the chemostat culture system
and a manL- and a manL-manH (encoding the heavy form of EIIMan) double
knockout derivatives of S. salivarius 57.I, and a manH-deficient derivative
of the codY-deficient S. salivarius, it was found that, in the absence of codY,
ManL and ManH repress the urease activity in cells grown at neutral pH,
indicating that Man-PTS only fine tunes urease expression. As both acidic
pH and excess lactose upregulated non-phosphorylated ManH production,
it is suggested that when less amount of phosphorylated ManH is available
for regulation, the repression by Man-PTS on urease is greatly reduced.
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