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Abstract:
Production of an extracellular matrix is essential for biofilm
formation, as this matrix both secures and protects the cells it
encases. Mechanisms underlying production and assembly of matrices are
poorly understood.Vibrio cholerae, relies heavily on biofilm formation
for survival, infectivity, and transmission. Biofilm formation
requiresVibriopolysaccharide (VPS), which is produced
byvpsgene-products, yet the function of these products remains unknown.
Here, we demonstrate that thevpsgene-productsvpsOandvpsUencode
respectively for a tyrosine kinase and a cognate tyrosine phosphatase.
Collectively, VpsO and VpsU act as a tyrosine phosphoregulatory system
to modulate VPS production. We present structures of VpsU and the kinase
domain of VpsO, and we report observed autocatalytic tyrosine
phosphorylation of the VpsO C-terminal tail. The position and amount of
tyrosine phosphorylation in the VpsO C-terminal tail represses VPS
production and biofilm formation through a mechanism involving the
modulation of VpsO oligomerization. We found that tyrosine
phosphorylation enhances stability of VpsO. Regulation of VpsO
phosphorylation by the phosphatase VpsU is vital for maintaining native
VPS levels. This study provides new insights into the mechanism and
regulation of VPS production and establishes general principles of
biofilm matrix production and its inhibition.
Author summary The biofilm life style protects microbes from a plethora
of harm, to increase their survival and pathogenicity.
Exopolysaccharides are the essential glue of the microbial biofilm
matrix, and loss of this glue negates biofilm formation and renders
cells more sensitive to antimicrobial agents. Here, we show that a
tyrosine phosphoregulatory system controls the biosynthesis and
abundance ofVibrioexopolysaccharide (VPS), an essential biofilm
component of the pathogenVibrio cholerae. The phosphorylation state of
the tyrosine autokinase VpsO, mediated by the tyrosine phosphatase VpsU,
directly modulates VPS production and also affects the kinase's own
degradation, to regulate VPS production. This study provides new
insights into the mechanisms ofV.choleraebiofilm formation and
consequently ways to combat pathogens more broadly, due conservation of
tyrosine phosphoregulatory systems among exopolysaccharide producing
bacteria.
