Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Biofilm formation and dynamic behavior

67

•

and to develop new biodegradable compounds to replace haz-

ardous chemicals in industrial activity. Research is, therefore,

aimed at bioremediation, which could identify biological

agents that rapidly degrade existing pollutants in the environ-

ment, such as heavy metals and toxic chemicals in soil and

water, explosive residues, or spilled petroleum. Crude oil

however, is naturally biodegradable, and species of hydrocar-

bon-degrading bacteria are responsible for an important reduc-

tion of petroleum levels in reservoirs, especially at

temperatures below 176° F (80° C). The selection, culture,

and even genetic manipulation of some of these species may

lead to a bioremediation technology that could rapidly degrade

oil accidentally spilled in water.

The search for a biodegradable substitute for plastic

polymers, for instance, is of high environmental relevance,

since plastic waste (bags, toys, plastic films, packing material,

etc.) is a major problem in garbage disposal and its recycling

process is not pollution-free. In the 1980s, research of polyhy-

droxybutyrate, a biodegradable thermoplastic derived from

bacterial metabolismwas started and then stalled due to the

high costs involved in fermentationand extraction. Starch is

another trend of research in the endeavor to solve this prob-

lem, and starch-foamed packing material is currently in use in

many countries, as well as molded starch golf tees. However,

physical and chemical properties of starch polymers have so

far prevented its use for other industrial purposes in replace-

ment of plastic. Some scientists suggest that polyhydroxybu-

tyrate research should now be increased to benefit from new

biotechnologies, such as the development of transgenic corn,

with has the ability to synthesize great amounts of the com-

pound. This corn may one day provide a cost-effective

biodegradable raw material to a new biodegradable plastics

industry.

Another field for biodegradable substances usage is the

pharmaceutical industry, where biomedical research focuses

on non-toxic polymers with physicochemical thermo-sensitiv-

ity as a matrix for drug delivering. One research group at the

University of Utah at Salt Lake City in 1997, for instance, syn-

thesized an injectable polymer that forms a non-toxic

biodegradable hydro gel that acts as a sustained-release matrix

for drugs.

Transgenic plants expressing microbial genes whose

products are degradative enzymesmay constitute a potential

solution in the removal of explosive residues from water and

soils. A group of University of Cambridge and University of

Edinburgh scientists in the United Kingdom developed trans-

genic tobacco plants that express an enzyme (pentaerythritol

tetranitrate reductase) that degrades nitrate ester and nitro aro-

matic explosive residues in contaminated soils.

Another environmental problem is the huge amounts of

highly stable and non-biodegradable hydrocarbon compounds

that are discarded in landfills, and are known as polyacry-

lates. Polyacrylates are utilized as absorbent gels in dispos-

able diapers, and feminine hygieneabsorbents, as well as

added to detergents as dispersants, and are discharged

through sewage into underwater sheets, rivers, and lakes. A

biodegradable substitute, however, known as polyaspartate,

already exists, and is presently utilized in farming and oil

drilling. Polyaspartate polymers are degradable by bacteria

because the molecular backbone is constituted by chains of

amino acids; whereas polyacrylates have backbones made of

hydrocarbon compounds.

The main challenge in the adoption of biodegradable

substances as a replacement for existing hazardous chemicals

and technologies is cost effectiveness. Only large-scale pro-

duction of environmental friendly compounds can decrease

costs. Public education and consumer awareness may be a cru-

cial factor in the progress and consolidation of “green” tech-

nologies in the near future.

See alsoAmino acid chemistry; Biotechnology; Economic

uses and benefits of microorganisms; Transgenics; Waste

water treatment

BIOFILM FORMATION AND DYNAMIC

BEHAVIORBiofilm formation and dynamic behavior

Biofilms are populations of microorganismsthat form follow-

ing the adhesion of bacteria, algae, yeast, or fungito a surface.

These surface growths can be found in natural settings, such

as on rocks in streams, and in infections, such as on catheters.

Both living and inert surfaces, natural and artificial, can be

colonized by microorganisms.

Up until the 1980s, the biofilm mode of growth was

regarded as more of a scientific curiosity than an area for seri-

ous study. Then, evidence accumulated to demonstrate that

biofilm formation is the preferred mode of growth for

microbes. Virtually every surface that is in contact with

microorganisms has been found to be capable of sustaining

biofilm formation.

The best-studied biofilms are those formed by bacteria.

Much of the current knowledge of bacterial biofilm comes

from laboratory studies of pure cultures of bacteria. However,

biofilm can also be comprised of a variety of bacteria. Dental

plaqueis a good example. Many species of bacteria can be

present in the exceedingly complex biofilm that form on the

surface of the teeth and gums.

The formation of a biofilm begins with a clean, bacte-

ria-free surface. Bacteria that are growing in solution (plank-

tonic bacteria) encounter the surface. Attachment to the

surface can occur specifically, via the recognition of a surface

receptor by a component of the bacterial surface, or non-

specifically. The attachment can be mediated by bacterial

appendages, such as flagella, cilia, or the holdfast of

Caulobacter crescentus.

If the attachment is not transient, the bacterium can

undergo a change in its character. Genes are stimulated to

become expressed by some as yet unclear aspect of the sur-

face association. This process is referred to as auto-induction.

A common manifestation of the genetic change is the produc-

tion and excretion of a large amount of a sugary material.

This material covers the bacterium and, as more bacteria

accumulate from the fluid layer and from division of the sur-

face-adherent bacteria, the entire mass can become buried in

womi_B 5/6/03 1:09 PM Page 67