2. BASIC PRINCIPLE
BASIC PRINCIPLE
FORMATION OF BIOFILMS, STRUCTURE AND
BEHAVIOUR OF BIOFILMS
3. BIOFILMS
Biofilms are assemblages of microbial cells attached to
each other and/or to a surface, encased within a self-
produced matrix.
The matrix consists of microbial biopolymers including
proteins, exopolysaccharides and extracellular DNA,
creating a distinct microenvironment. Thus, for many
microbes (including bacteria and archaea, as well as
unicellular eukaryotes such as amoeba, flagellates,
diatoms and unicellular algae), biofilm formation protects
the microbial community from environmental stressors
4. IN ENVIRONMENT
Microorganisms well adapted to processes in
environmental biotechnology are almost always found in
naturally occurring aggregates. Engineers exploit natural
aggregation as means to separate the microorganisms
from the effluent water, thereby providing a good
effluent quality while concurrently retaining a large
bionlass concentration in the treatment system.
The two types of aggregates Suspended flocs
Attached biofilms.
Flocs and biofilms differ in that biofilms adhere to a solid
substratum, while flocs are formed without a solid
substratum.
.
5. Biofilms are ubiquitous and play critical
roles in natural and anthropogenic
environments. Biofilm communities are
important for ecosystem functioning,
driving biogeochemical processes, nutrient
cycling and bioremediation.
6. NATURE OF BIOFILM
Biofilms represent a sessile developmental stage in
the life of unicellular microbial organisms. Based on
this view, biofilm-forming organisms undergo a life
cycle that involves both sessile and motile stages.
In this life cycle, biofilm formation is initiated by the
attachment of cells to a substratum, followed by the
proliferation and recruitment of cells from the
surrounding environment. Cells in the biofilm then
form microcolonies, which mature, and eventually
disperse as motile cells and/or cell aggregates
released from microcolonies. These spread and
serve as inocula for new biofilm initiation and
development.
7.
8. Image at the right shows pitting and
corrosion of a stainless steel surface. This
was caused by a biofilm, whose presence
influenced how and how fast minerals were
deposited on the surface. This, in turn,
modified the electrochemical properties of
the stainless steel, which caused the pitting
corrosion of this seemingly impervious metal.
9. CHARACTERISTICS COMMON TO ALL
OBSERVED BIOFILMS
:
biofilms are dynamic and responsive to their environment; that
is, they can adapt to changes in their environment.
A phenomenon known as detachment seems to be common
among all biofilms. Bacterial cells can detach from their biofilm
colony individually or in clumps.
When individual microorganisms detach from a biofilm, these
isolated microorganisms are relatively easy to kill with
chemicals designed for this purpose.
when microorganisms detach from their biofilm colony in
clumps, the clumps are pieces of the biofilm that are at the
moment not attached to a surface; in this case they maintain
the protective properties of the original biofilm and are thus
much more difficult to kill.
In the right conditions, biofilms can migrate across surfaces
over a period of time in a variety of ways,.
11. HABITATS
Biofilms are ubiquitous in organic life. Nearly every
species of microorganism have mechanisms by
which they can adhere to surfaces and to each
other. Biofilms will form on virtually every non-
shedding surface in non-sterile aqueous or humid
environments.
Biofilms can grow in the most extreme
environments: from, for example, the extremely hot,
briny waters of hot springs ranging from very acidic
to very alkaline, to frozen glaciers.
12. HABITATS
Mats of bacterial biofilm color the hot
springs in Yellowstone National Park. The
longest raised mat area is about half a
meter long.
Biofilms can be found on rocks and
pebbles at the bottoms of most streams
or rivers and often form on the surfaces
of stagnant pools of water. Biofilms are
important components of food chains in
rivers and streams and are grazed by
the aquatic invertebrates upon which
many fish feed.
13. CHARACTRISTICS /BEHAVIOUR OF
BIOFILMS
Biofilm cells can coordinate behavior via intercellular
"communication" using biochemical signaling molecules
Another characteristic of cells found in a biofilm is that they
can communicate with each other. Really, in order for any
community to succeed, there must be good communication
among its members. Biofilm communities appear to be no
different One of the fascinating aspects of bacterial community
living is that it provides a setting for bacteria to communicate
using chemical signals. There is evidence that some of these
chemical signals, produced by cells and passed through their
outer membranes, may be interpreted not just by members of
the same cell species, but by other microbial species that are
part of the same biofilm community — and perhaps even by
more complex organisms in some cases. The sensing of
these chemical signals by neighboring cells in the biofilm can
cause the neighboring cells to behave differently.
14. Different strains of bacteria must live together in obligate
consortia for substrate transport or some other synergistic
relationships;the close juxtaposition of cells in a biofilm is
necessary for the exchanges.
The biofilms create an internal environment (e.g., pH,
that is more hospitable than the bulk liquid. In other words,
the biofilm generates unique, self-created microenvironments
that benefit the cells.
The surface itself creates a unique microenvironment, such
as by adsorption of toxins or corrosive release of Fe2+,
which is an electron donor
16. IMORTANCE IN ENVIRONMENT
. Biofilms, which are naturally immobilized cells,
occur ubiquitously in nature and are increasingly
important in engineered processes
used in pollution control, such as trickling filters,
rotating biological contactors, and anaerobic filters
Biofilm processes are simple, reliable, and stable
because natural immobilization allows excellent
biomass retention and accumulation without the
need for separate solids-separation devices.
20. ATTACHMENT
The formation of a biofilm begins with the attachment of free-
floating microorganisms to a surface
The first colonist bacteria of a biofilm may adhere to the surface
initially by the weak van der Waals forces and hydrophobic
effects.[
If the colonists are not immediately separated from the surface,
they can anchor themselves more permanently using cell
adhesion structures such as pili. A unique group of Archaea that
inhabit anoxic groundwater have similar structures called hami.
Each hamus is a long tube with three hook attachments that are
used to attach to each other or to a surface, enabling a
community to develop
Hyperthermophilic archaeon Pyrobaculum calidifontis produce
bundling pili which are homologous to the bacterial TasA
filaments, a major component of the extracellular matrix in
bacterial biofilms, which contribute to biofilm stability
TasA homologs are encoded by many other archaea, suggesting
mechanistic similarities and evolutionary connection between
bacterial and archaeal biofilms
21. CONDITIONING
A clean surface is immediately covered with a
conditioning film of organic molecules and
macromolecules.
Transport of molecules and small particles is rapid
and as a result adsorption of conditioning film
occurs instantaneously •
The presence o f the condiionig film alters the
characteristics of the substratum.
