As mentioned above, QS is used as a signal for the cell to
form biofilms, which represent the prevalent microbialmode
of existence in nature (Flemming & Wingender, 2010). Such
structures confer protection against environmental stresses
as well as antibiotics and play critical roles in microbial
pathogenesis. In addition, the formation of biofilms (switching
from the planktonic to the surface-associated mode of
growth) requires complex regulatory cascades. In E. coli, the
two sRNAs CsrB and CsrC (already known to interact with
CsrA, see ‘sRNA and cellular metabolism’ above) activate
FlhDC (encoding a flagellar master regulator) and downregulate
the expression of the pga operon, encoding a poly-
N-acetyl-D-glucosamine extracellular matrix, one of the
biofilm components (Mika & Hengge, 2013).