Objectives
The objectives of this section are:
to give you a glimpse of the wide variety of environments in which
biofilms grow
to give you basic knowledge of the negative effects of biofilms
grown on industry and medicine
to help you understand that biofilms are a naturally occurring and
often beneficial phenomenon on earth
Outcomes
Upon completion of this section students will be able to:
recognize possible biofilm formations in the natural environment
appreciate the effect of harmful biofilms on industry
realize the harmful result of biofilms that grow on medical
equipment and implants.
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Section 2:
Where do biofilms grow?
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Test your
knowledge |
Go to Section
Three |
About Section 2
In this section we provide you with a glimpse of the many places in
which one can expect to find biofilms. The surprising thing is that they
seem to be everywhere. At least everywhere that has the remotest
possibility of sustaining life. Recognizing this fact helps us understand
the nature of biofilms and may help us learn how to treat harmful biofilms
and how to exploit beneficial biofilms for good.
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What a biofilms need to grow
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BIOFILMS grow just about anywhere. All it takes is:
- microorganisms
- moisture
- nutrients
- surfaces
Many, many different organisms, such as bacteria, can form a biofilm
colony. As noted in section 1 of this module, over 500 different
microorganisms have been found in typical dental plaque. Such
microorganisms are all around us, on us, and in us.
What kind of moisture is needed? Biofilms grow in fresh water, salt water,
oil pipelines, in the human body, and, well, you name it. Just about any
kind of naturally occurring moisture will do.
What biofilms feed on is just as varied. Certain biofilms even thrive on
petroleum oil. Interestingly, the capacity of this kind of biofilm to
gobble oil has both a bad and a good side. Oil-eating biofilms can grow in
and clog an oil pipeline; they can also be used to clean up an oil spill.
As discussed in section 1, to form a biofilm, microorganisms must "glue"
themselves to a surface, form colonies, and reproduce. Virtually any
surface will serve the purpose: rocks, countertops, human tissue, and so
forth.
In the remaining subsections below, we identify some specific environments
that support biofilm growth that are of interest to biofilm engineers and
scientists.
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Natural environments
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As we stated above, biofilms grow virtually everywhere, in
almost any environment where there is a combination of moisture,
nutrients, and a surface.
As one might suspect, biofilms grow in rain forests in many
different forms, such as moss, or lichen, on tree trunks. There is,
after all, an abundance of moisture, nutrients and surfaces in a
rain forest. What one might not suspect is that biofilms also grow
in deserts. One common form of desert biofilm is known as "desert
varnish," a term descriptive of the fact that the rocks, canyon
walls, or sometimes entire mountain ranges on which they grow
appear to be varnished with a reddish or other colored stain.
Indeed, petroglyphs left on boulders and cave walls by early desert
dwellers were often formed by scraping through the coating of desert
varnish formations with a hard object.
The wide variety and adaptability of the microorganisms that form
biofilms is evident in the extremes of environments—very hot to
very cold—in which they are found. Microorganisms that thrive in
such extreme environments are known as extremophiles, a
self-descriptive term. Such microorganisms (for example, bacteria)
can, and do, form biofilm colonies even in such environments.
They have been found at the bottom of the ocean
near extremely hot ocean vents. Indeed, they seem to be the first
living things to grow around newly formed vents. Other biofilms have
been found living on glaciers in the Antarctic.
Yellowstone National Park in the United States offers
visitors an amazing display of biofilms that grow as slimy algae in
and around the many geysers, hot springs, and warm streams in the
Park. |
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This streambed in Yellowstone National Park is
coated with biofilm that is several inches thick in places. The
warm, nutrient-rich water provides an ideal home for this biofilm,
which is heavily populated by green algae. The microbes colonizing
thermal pools and springs in the Park give them their distinctive
and unusual colors. More examples of these extremophilic bacterial
communities can be viewed in the slide show below. Photo,
above, courtesy of D. Davies. |
Depending on the water temperature in which they are found,
the algae display a dazzling array of beautiful colors that are the
subject of many a fine photograph. As stream flows change in the
Park, colorful algae formations go dormant and turn a lifeless gray
in dry stream beds. But not to worry. New algae growth springs up in
the new stream beds, lending a dynamic, ever-changing view of the
thermal features.
Biofilms are also an important life link in many ecological
communities. The microorganisms that make up biofilms form the basis
for food webs that nourish larger organisms such as insect larvae,
which are consumed by fish, that are in turn consumed by birds and
other animals.
Even plants can benefit from naturally occurring biofilms. One
beneficial type of plant-biofilm relationship occurs in the plant
roots. Plant roots secrete significant amounts of sugars, amino
acids, vitamins and plant hormones that serve as nutrients for
biofilms to grow on root hairs. This growth may facilitate the
plant's ability to absorb nutrients from the soil. So a mutually
beneficial relationship can exist between plants and biofilms.
You may wonder how biofilms get their start in such diverse
environments. If there aren't any biofilms in a particular area,
but, say, a new thermal feature suddenly develops in an area like
Yellowstone National Park, or a new, hot vent opens up on the floor
of the ocean, how does a biofilm form there? Here's how. It is known
that the entire globe—both above and below ground—is "seeded" with
the microorganisms that form biofilm colonies. They flourish,
disperse, or become dormant depending on changing environmental
conditions. That is, all of the ingredients for biofilm
formation—microorganisms, moisture, nutrients, and surfaces—are
just a natural part of our natural environment.
These ingredients are indeed all around us, on us, and in us.
Back to top
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Slide show to come: Biofilms in natural
environments |
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Manufactured materials and systems
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Whereas biofilms in nature tell a good story that
helps us understand the biology of our world, biofilms in industry
are slime of a different nature. It seems that biofilms are the
culprits in a number of problems faced in industry.
We can relate a few examples of biofilm problems that plague
industry. For example, biofilm contamination and fouling (sometimes
referred to as biofouling) occur in nearly every industrial
water-based process, including water treatment and distribution,
pulp and paper manufacturing, and the operation of cooling towers.
Biofilms are responsible for billions of dollars in lost industrial
productivity, as well as product and capital equipment damage each
year. Biofilms are notorious for causing pipe plugging, pipe
corrosion and water contamination.
Rather than continue with a long list of examples, we will just
present you with a slide show that illustrates instances of
biofouling in industry.
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Slide show: Biofilms affect
manufactured materials and systems |
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Health and the human body
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This may come as something of a shock to you, but
about 90 percent of the cells in a human body are not human! In fact,
the human body is heavily colonized by microbes that have found it a
great place to live. We have communities of microbes living on all
mucous surfaces and in our digestive tract, as well as on and in
layers of our skin. For the most part we all get along; in fact, we
depend on some of our gut microbes to help with digestion.
Sometimes, however, the microbial load causes problems of infection.
Dentists now understand, for instance, that dental caries (cavities)
are the result of bacterial infection (and biofilms!). When the
normal balance of microbial populations is upset or when our immune
system is overwhelmed, we can have a real battle with microbial
opportunists.
In the 1990s, as the
biofilm concept was being introduced to the medical community,
doctors began to make the connection between chronic, low-grade
infections and the biofilm mode of growth. Dental professionals made
the connection easily, as teeth could readily be scraped for
microscopic examination. Internal cases of chronic infection have
taken longer to prove, but testing has shown that many troublesome
diseases have entrenched microbial populations at their core. Peptic
ulcers, once thought to be caused by stress, have been proved to be
caused by bacterial communities of Helicobacter pylori. The
cyclical flare-up and subsidence of otitis media—the most common
cause of children's recurrent earaches—is an example of a typical
biofilm-based infection. Click to see
Table 1-2, a summary of
biofilms in medical contexts, the associated impacts, and journal
references. More detailed
information is available in MODULE 7: BIOFILMS IN MEDICAL
CONTEXTS, to come.
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Test your
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Three |
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Module 1 Intro page
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