House of biofilm cells

The EPS Matrix: The “House of Biofilm Cells”
J. Bacteriol. 2007, 189(22):7945. DOI: 10.1128/JB.00858-07.
Hans-Curt Flemming, Thomas R. Neu and Daniel J.
Wozniak

This paper was written as a
summary of discussions about EPS (extracellular polymeric substances) of
biofilms between some leading researchers. EPS determines the biofilm cells
immediate environment by affecting porosity, density, water content, charge,
sorption properties,
hydrophobicity, and mechanical stability. It is made up of polysaccharides,
proteins, glycoproteins, glysolipids and extracellular DNA (e-DNA). However
there may be much more as it is very difficult to separate the EPS from the
cells and analysis of complex carbohydrates is also difficult.

Sorption properties of the EPS help in
attatchment to a surface and attracts particulates from the environment for
food. EPS is often a preferred food source than the cells themselves to
preditors and therefore provides protection. Within Biofilms easy exchange of
genetic material, that maintains a large gene pool, is possible as cells are
kept close together and are able to move around. Cellulose has been
found to be a component of EPS in amoebae, algae and bacteria. It is important
in infectious processes when co-expressed with curli fimbriae. E-DNA was thought to be a remnant of lysed cells but now seems to have
a structural role and could be used by cells as nanowires to move along. It was
also speculated that they might be used for electron transfer or communication.
There must be good uses of the e-DNA molecules to warrant the expense of
producing them.

The concept of an active matrix is that the EPS
retains enzymes and membrane vesicles that carry genetic material and enzymes
that provide nutrition and maybe resistance to inimical agents. They also play
apart in the biological warfare that goes on in the matrix containing lytic
enzymes and virulence factors.

The paper warned that although
much research on biofilms uses P. aeruginosa, because it is the first to
colonize cystic vibrosis patients, it is not suitable for extrapolation to
general biofilms. Environmental biofilms differ in that they contain less
alginate and charged polysaccharides. Natural biofilms can also follow cyclic
patterns. The complexity of EPS makes modelling difficult and many aspects
remain to be addressed such as the EPS function in biocide resistance and how
the cells maintain the matrix with species dynamics being crucial. Further understanding requires more
sensitive and less-destructive new methods to allow for the investigation of
biofilm processes in situ over time. The concept that the biofilm is a tissue
(Costerton and Irvin 1981) is not a stupid one.