Influence of Biofilms on Porous Media Hydrodynamics - Porous Media: Applications in Biological Systems and Biotechnology - page 175

acknowledged with the republication of a “vintage article” along with a
commentary in biotechnology and bioengineering (Characklis and Bryers
2008).
It took until 1990 for the first topic on biofilms to appear. Two of the
pioneers in biofilm research, Kevin Marshall and Bill Characklis coedited
Biofilms , a topic still very worthwhile for the beginning biofilm engineer
or microbiologist (Characklis and Marshall 1990). Over the past 20 years,
numerous topics on biofilms have been published, and the interested reader is
encouraged to consult those for more detail (Characklis and Marshall 1990;
Lappin-Scott and Costerton 1995; Bryers 2000; Evans 2000; Ghannoum and
O'Toole 2004; Costerton 2007; Lewandowski and Beyenal 2007). In addition,
the Center for Biofilm Engineering at Montana State University is spearhead-
ing an effort to develop the “Biofilm Hypertextbook,” which can currently be
accessed at http://www.biofilmbook.com/.
Biofilms are complex three-dimensional microbial communities attached
to a surface (Figure 5.1). There is no one commonly accepted definition for
the term “biofilm,” although it is generally agreed upon that a biofilm is
an aggregate of microorganisms, such as bacteria, algae, fungi, or protozoa,
attached to a surface and embedded in a self-produced matrix of EPS. Biofilms
can be found on various surfaces and in various industrially, environmentally,
and medically relevant systems. They form in completely saturated as well
as unsaturated environments such as pipelines, soils, medical implants, blood
vessels, biomaterials, tissues, biofilters, cooling towers, ship hulls, river rocks,
and a variety of other environments. One of the major differences between
suspended cells and biofilms is the commonly large amount of EPS present in
biofilms, which, among other potential roles, provides biofilms with structural
support. Biofilm communities have been argued to be the predominant form
of microbial life in many environments (Costerton et al . 1995; Stoodley et al .
2002b; Costerton 2007), and especially in systems with high surface area to
volume ratios, such as porous media, biofilm communities can be expected to
dominate (VanLoosdrecht et al . 1990; Bouwer et al . 2000).
The biofilm mode of growth can have significant competitive advantages.
Immobilized organisms (e.g., a biofilm on soil particles) in a continuous-flow
system (e.g., flowing groundwater containing growth substrates) will have a
continuous supply of substrates and nutrients from the flowing fluid or the
porous medium itself.
In general, three stages of biofilm development are to be considered:
(1) Microbial transport and attachment, (2) biofilm growth, and (3) micro-
bial detachment and propagation. Two animations (Movies 7 and 8) were
published as supplementary materials to “The Biofilm Primer” at http://
www.springer.com/life+sciences/microbiology?SGWID=0-10037-12-322199-0
(Costerton 2007) and are recommended to be viewed by the novice in this
field.