Gram-positive bacteria use peptides as auto-inducing (AI) signals to regulate adaptive
processes such as production of public goods (extracellular molecules that can be
shared by the community). ComX is an AI peptide, mostly known for its role in the
regulation of bacterial competence and surfactin production in Bacillus subtilis. These
two traits are regulated accordingly to the bacterial population size, thus classifying
ComX as a quorum sensing (QS) signal. We used this peptide-based AI system (the
ComQXPA system), as a model to explore the links between cell-cell communication,
exoprotease production and biofilm matrix production. The positive regulation of
public goods (e.g. biofilm matrix components and exoproteases) by AI molecules in
bacteria has been implied by several existing theories and experiments. In order to
further corroborate these assumptions, we tested two hypotheses, predicting that the
inactivation of the B. subtilis cell-cell communication system will have a negative
impact on the production of exoproteases and biofilm matrix components. We also
investigated the potential of ComX regulated proteases to degrade the ComX AI
peptide. Obtained results confirmed that ComX plays an important role in exoprotease
synthesis. Additionally, we confirmed that the ComX regulated exoproteases can
degrade this signaling peptide. However, we also observed that the ComQXPA QS
system slows down the overall production of biofilm matrix components and promotes
sporulation. The floating biofilms of ComX deficient mutants produce more matrix
components, more cells but less spores at an early stage of biofilm formation and
exhibit a more synchronous induction into sporulation at the later stage. These results
suggest that the ComQXPA QS system serves as a switch that down modulates
investment into growth and biofilm formation and assures early investment into
sporulation and aforementioned late growth adaptations.
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