The Role of Quorum Sensing in Biofilm Development - Antibiofilm Agents: From Diagnosis to Treatment and Prevention - page 96

2 The Connection Between QS and Biofilms
Many factors influence the ability of microbes to construct biofilms. Environmental
conditions such as the availability of nutrients, composition of the microbial
population, surface properties, flow, and other physical forces will all affect the
temporal sequence of biofilm developmental stages. For many microbes, the ability
to “communicate” is advantageous for building biofilms. Intuitively this makes
sense. It would be almost impossible for a team of construction workers to erect a
skyscraper without the ability to communicate with each other. In the biblical
Tower of Babylon story, God thwarted the people's plan to build a tower to heaven
by cursing them with the inability to communicate. Similarly, it is assumed that the
ability of many microbes to build biofilms can also be thwarted if microbial
communication is inhibited.
The first published study that linked QS with biofilm formation demonstrated
that P. aeruginosa lasI mutants, who were unable to synthesize 3OC 12 -HSL,
formed biofilms that were flat, undifferentiated, and less resistant to dispersion
with sodium-dodecyl sulfate than biofilms made by their wild-type parent strain
(Davies et al. 1998 ). In the interim 15 years, many reports have been published that
link QS and biofilm formation by several different organisms (see Table 1 for
examples). Parsek and Greenberg ( 2005 ) proposed that QS and biofilms have been
inextricably linked because both areas of study consider social phenomena
exhibited by bacteria and thus suggested the term “sociomicrobiology” be used to
encompass both. However, while QS and biofilms tend to be lumped together, our
understanding of how, and under what circumstances, QS influences biofilm for-
mation is still very limited. And while it may be intuitive that biofilm formation
relies on bacterial communication, this is not always the case. The QS systems of
several different microorganisms either negatively influence different stages of
biofilm formation (Table 1 ) or have no effect on it. Y. pestis is an example of a
bacterial species whose QS system is apparently not involved in biofilm formation
(Jarrett et al. 2004 ).
3 QS-Dependent Biofilm Processes
It is generally accepted that for many microbes QS plays an important, if not
essential, role in their ability to construct optimal biofilms. This notion is based
on numerous studies with several different microbial species that have demon-
strated altered biofilm formation by QS mutants. However, observing that a mutant
forms a biofilm with less or more biomass, or an altered three-dimensional shape,
than a wild-type strain after a defined amount of time does not tell us what processes
were deficient or what fitness consequences this has for the mutant. The formation
of a biofilm is a dynamic process. In general, biofilm formation involves five
different stages (Stoodley et al. 2002 ) (Fig. 2 ): (1) Reversible attachment of the