Three major proteases, elastase B (LasB), protease IV (PIV),
and elastase A (LasA) expressed in Pseudomonas aeruginosa
play important roles in infections and pathogeneses. These
are activated by a proteolytic cascade initiated by the activation
of LasB. In this study, we investigated whether LasB
could be inhibited using its propeptide (LasBpp). Although
LasA and PIV were inhibited by their propeptides, LasB was
not inhibited by purified LasBpp because LasB degraded LasBpp.
To address this problem, mutant LasBpp variants were constructed
to obtain a mutant LasBpp resistant to LasB degradation.
A C-terminal deletion series of LasBpp was tested in
vivo, and two positive candidates, T2 and T2-1, were selected.
However, both caused growth retardation and were unstably
expressed in vivo. Since deleting the C-terminal end of LasBpp
significantly affected its stable expression, substitution mutations
were introduced at the two amino acids near the
truncation site of T2-1. The resulting mutants, LasBppE172D,
LasBppG173A, and LasBppE172DG173A, significantly diminished LasB
activity when overexpressed in vivo and were stably expressed
in MW1, a quorum sensing mutant that does not produce
LasB. In vitro analysis showed that purified LasBppE172DG173A
inhibited LasB activity to a small extent. Summarizing, Cterminal
modification of LasBpp profoundly affected the stable
expression of LasBpp, and little enhanced the ability of
LasBpp to resist degradation by LasB.
Streptococcus gordonii, a Gram-positive commensal bacterium,
is an opportunistic pathogen closely related to initiation
and progression of various oral diseases, such as periodontitis
and dental caries. Its biofilm formation is linked
with the development of such diseases by enhanced resistance
against antimicrobial treatment or host immunity. In the
present study, we investigated the effect of short-chain fatty
acids (SCFAs) on the biofilm formation of S. gordonii. SCFAs,
including sodium acetate (NaA), sodium propionate (NaP),
and sodium butyrate (NaB), showed an effective inhibitory
activity on the biofilm formation of S. gordonii without reduction
in bacterial growth. SCFAs suppressed S. gordonii
biofilm formation at early time points whereas SCFAs did
not affect its preformed biofilm. A quorum-sensing system
mediated by competence-stimulating peptide (CSP) is known
to regulate biofilm formation of streptococci. Interestingly,
SCFAs substantially decreased mRNA expression of comD
and comE, which are CSP-sensor and its response regulator
responsible for CSP pathway, respectively. Although S. gordonii
biofilm formation was enhanced by exogenous synthetic
CSP treatment, such effect was not observed in the
presence of SCFAs. Collectively, these results suggest that
SCFAs have an anti-biofilm activity on S. gordonii through
inhibiting comD and comE expression which results in negative
regulation of CSP quorum-sensing system. SCFAs could
be an effective anti-biofilm agent against S. gordonii for the
prevention of oral diseases.
Citations
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