Beneficial biofilm grows on all surfaces in water
Putting new surface-area into water attracts the benefical microbes that carry out nature’s cleaning processes.
If you have ever slipped on a river rock, or picked up a slimy stick to throw for your dog, you've encountered biofilm. That "icky slime" teems with microscopic life invisible to the human eye. It is both the foundation of the aquatic food web and the natural system for cleansing water. As oxygen is to water chemistry, biofilm is to aquatic biology. When there's plenty of both, clean healthy water is enjoyed.
Plant matter – phytoplankton – will stick to biofilm and form periphyton, those dangly green fronds that you see drifting below the water surface. Periphyton harbors myriad life forms. Under a microscope, you’ll see a jungle alive with tiny “lions and tigers”, all eating each other and being eaten, absorbing nutrients as they grow and feeding the next layer of the food web. It is constantly being renewed. Biofilm and periphyton are ofter referred to interchangeably.
Periphyton begins to form on this biofilm-coated surface of BioHaven matrix
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Under the microscope, you can see a jungle of teeming life-forms within the biofilm / periphyton
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BioHaven Floating Island matrix has a tremendous amount of surface area on which biofilm can grow - bio-reactive surface area - that is more approachable, affordable and less intense than highly engineered mechanical bioreactors. Yet it does the same thing: provides surface area for the growth of biofilm for cleaning up water.
Dr Mark Reinsel, PE, a graduate of Montana State University’s Center for Biofilm Engineering is FII’s Process Engineer and has worked in the field of water remediation using biofilm reactors for several decades. He wrote the following paragraphs as an online course to help non-scientists gain an understanding of biofilm.
What Is A Biofilm?
A biofilm is a community of microorganisms attached to a solid surface. A biofilm community can include bacteria, fungi, yeasts, protozoa and other microorganisms.
Biofilms form when these microorganisms attach to surfaces exposed to water, and begin to excrete a slimy, glue-like substance (called extracellular polymer substances or EPS). Colonies of biofilm bacteria carry out a variety of detrimental or beneficial reactions that affect all of us daily.
While it may seem that microbiologists are always striving for pure cultures (containing only one species of bacteria), nearly all of the bacteria in the world live in micro-ecosystems filled with hundreds of different kinds of other microorganisms. Most of the microorganisms are not free-floating (as we may imagine in a test tube); rather, they attach themselves to surfaces in complex communities called biofilms.
A biofilm is a community of microorganisms attached to a solid surface. A biofilm community can include bacteria, fungi, yeasts, protozoa and other microorganisms.
Biofilms form when these microorganisms attach to surfaces exposed to water, and begin to excrete a slimy, glue-like substance (called extracellular polymer substances or EPS). Colonies of biofilm bacteria carry out a variety of detrimental or beneficial reactions that affect all of us daily.
While it may seem that microbiologists are always striving for pure cultures (containing only one species of bacteria), nearly all of the bacteria in the world live in micro-ecosystems filled with hundreds of different kinds of other microorganisms. Most of the microorganisms are not free-floating (as we may imagine in a test tube); rather, they attach themselves to surfaces in complex communities called biofilms.
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Why and How Do These Biofilms Form?
Bacteria become attracted to surfaces for a number of reasons. One may be gravity—organisms may just settle out and end up resting on a surface. Or bacteria (which often have a negative charge associated with their outer envelope) may be attracted to the positive charges on some inorganic surfaces. But there is evidence that biofilm formation is much more than random physical forces. Many surfaces attract and concentrate nutrients, and many bacteria have the capacity to detect and move toward high concentrations of nutrients (an ability called chemotaxis). |
Here is a schematic showing biofilm formation during the processes of attachment, colonization and growth. “Planktonic” cells are free-floating, while “sessile” cells are attached (Schematic courtesy of P. Dirckx, Center for Biofilm Engineering)
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Biofilm forms when bacteria adhere to surfaces in aqueous environments and begin to excrete a slimy, glue-like substance that can anchor them to all kinds of material – such as metals, plastics, soil particles, medical implant materials and tissue. A biofilm can be formed by a single bacterial species (pure culture) but more often, biofilms consist of many species of bacteria, as well as fungi, algae, protozoa, debris and corrosion products. Essentially, biofilm may form on any surface exposed to bacteria and some amount of water. Once anchored to a surface, biofilm microorganisms carry out a variety of detrimental or beneficial reactions (by human standards), depending on the surrounding environmental conditions.
How Do Bacteria Develop into a Teeming, Activity Community?
Some cells are able to produce large amounts of polysaccharides (extracellular polymer substances or EPS), which act as mucus layers and hold the cells to the surface. These cells are called the primary colonizers. The external slime produced by the primary colonizers captures other bacteria (secondary colonizers), which live and grow off the waste products produced by the primary colonizers. Soon there is an extensive and complex microbial community, all contained inside the polysaccharide slime. This is the biofilm.
Some cells are able to produce large amounts of polysaccharides (extracellular polymer substances or EPS), which act as mucus layers and hold the cells to the surface. These cells are called the primary colonizers. The external slime produced by the primary colonizers captures other bacteria (secondary colonizers), which live and grow off the waste products produced by the primary colonizers. Soon there is an extensive and complex microbial community, all contained inside the polysaccharide slime. This is the biofilm.
What Are the Advantages of Living in a Biofilm?
1. Protection from Antibiotics
Scientists have shown that much higher concentrations of antimicrobial agents (antibiotics or biocides) are needed to kill bacteria in biofilms, compared to free-floating bacteria. Biofilm bacteria are called “attached” or “sessile” organisms, while free-floating bacteria are called “suspended” or “planktonic” organisms. Originally, it was assumed that the biofilm provided a physical barrier against the antimicrobial agent; scientists believed that the agent could not penetrate the biofilm. This may play a role in providing protection.
However, recent evidence suggests that the nature of the colonies themselves provides protection. By growing in microcolonies, the outer cells protect the inner cells from the antimicrobial agent that does penetrate the biofilm, leaving the inner cells to grow and multiply.
2. Concentration of Nutrients
Because negative charges are often associated with the biofilm matrix, many nutrients (particularly those with a positive charge, called cations) are attracted to the biofilm surface. In addition, nutrients with negative charges (anions) can exchange with ions on the surface. This provides bacterial cells within the biofilm with high concentrations of nutrients compared to the surrounding water. Therefore, attached cells have an inherent biological advantage over suspended cells.
1. Protection from Antibiotics
Scientists have shown that much higher concentrations of antimicrobial agents (antibiotics or biocides) are needed to kill bacteria in biofilms, compared to free-floating bacteria. Biofilm bacteria are called “attached” or “sessile” organisms, while free-floating bacteria are called “suspended” or “planktonic” organisms. Originally, it was assumed that the biofilm provided a physical barrier against the antimicrobial agent; scientists believed that the agent could not penetrate the biofilm. This may play a role in providing protection.
However, recent evidence suggests that the nature of the colonies themselves provides protection. By growing in microcolonies, the outer cells protect the inner cells from the antimicrobial agent that does penetrate the biofilm, leaving the inner cells to grow and multiply.
2. Concentration of Nutrients
Because negative charges are often associated with the biofilm matrix, many nutrients (particularly those with a positive charge, called cations) are attracted to the biofilm surface. In addition, nutrients with negative charges (anions) can exchange with ions on the surface. This provides bacterial cells within the biofilm with high concentrations of nutrients compared to the surrounding water. Therefore, attached cells have an inherent biological advantage over suspended cells.
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The image shows the geometry of the biofilm, with an inert substratum at the bottom and the bulk liquid at the top, separated from the growing biofilm by a mass transfer boundary layer at a constant height above the biofilm. The substrates (nutrients) diffuse downward from the bulk liquid through the boundary layer into the biofilm (courtesy of Cardiff School of Biosciences, Wales, UK)
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3. Microbial Communities
No bacterium is an island—that is, nearly all bacteria live with, and depend upon, other microorganisms for energy, carbon and other nutrients. The biofilm physically contains substances that are released by microorganisms, making them more available to other microbes in the biofilm.
A classic example of this is provided by the degradation of cellulose. Cellulytic microbes are able to break the cellulose into sugar monomers, which fermenting bacteria can use. Their fermentation products are smaller organic acids, carbon dioxide and hydrogen gas, which methanogenic (methane-producing) or sulfate-reducing bacteria can use as their carbon and energy sources. Therefore, cellulose-utilizing, fermenting, methanogenic and sulfate-reducing bacteria can all exist in a single biofilm.
Another example is aerobic versus anaerobic bacteria in a biofilm. Aerobic bacteria require oxygen, so they will be present in the outer layer of a biofilm which is exposed to oxygenated water. These aerobic bacteria will consume oxygen as the oxygenated water diffuses through the biofilm, so that the middle and inner layers of the biofilm may be anoxic (low oxygen concentration) or anaerobic (essentially zero oxygen). In this deeper section of the biofilm, one may expect to find nitrate-reducing, sulfate-reducing or methanogenic bacteria. Thicker biofilms will tend to have a wider diversity of microorganisms, as they support a vast array of microenvironments.
In addition to food (carbon) and energy sources, genetic material can be more easily exchanged within the confines of the biofilm. This increases the potential that new, better-adapted, strains of bacteria will evolve within the biofilm.
No bacterium is an island—that is, nearly all bacteria live with, and depend upon, other microorganisms for energy, carbon and other nutrients. The biofilm physically contains substances that are released by microorganisms, making them more available to other microbes in the biofilm.
A classic example of this is provided by the degradation of cellulose. Cellulytic microbes are able to break the cellulose into sugar monomers, which fermenting bacteria can use. Their fermentation products are smaller organic acids, carbon dioxide and hydrogen gas, which methanogenic (methane-producing) or sulfate-reducing bacteria can use as their carbon and energy sources. Therefore, cellulose-utilizing, fermenting, methanogenic and sulfate-reducing bacteria can all exist in a single biofilm.
Another example is aerobic versus anaerobic bacteria in a biofilm. Aerobic bacteria require oxygen, so they will be present in the outer layer of a biofilm which is exposed to oxygenated water. These aerobic bacteria will consume oxygen as the oxygenated water diffuses through the biofilm, so that the middle and inner layers of the biofilm may be anoxic (low oxygen concentration) or anaerobic (essentially zero oxygen). In this deeper section of the biofilm, one may expect to find nitrate-reducing, sulfate-reducing or methanogenic bacteria. Thicker biofilms will tend to have a wider diversity of microorganisms, as they support a vast array of microenvironments.
In addition to food (carbon) and energy sources, genetic material can be more easily exchanged within the confines of the biofilm. This increases the potential that new, better-adapted, strains of bacteria will evolve within the biofilm.
Where Are Biofilms Found?
The short answer is: everywhere. In nature, biofilms are found on most moist surfaces, on plant roots, and within nearly every living animal. They can be detrimental to humans by growing within human bodies (causing infections and other problems), and by growing on surfaces within aquatic systems (such as in pipelines, on the surface of heat exchangers and on the bottoms of boats). Often biofilms can be used to mankind’s advantage in a number of industrial processes. Primarily, biofilms help native bacteria do what they do best—grow and recycle all of the carbon and nutrients that other organisms produce, and provide humans with the type of environment to which we have become acclimated.
The short answer is: everywhere. In nature, biofilms are found on most moist surfaces, on plant roots, and within nearly every living animal. They can be detrimental to humans by growing within human bodies (causing infections and other problems), and by growing on surfaces within aquatic systems (such as in pipelines, on the surface of heat exchangers and on the bottoms of boats). Often biofilms can be used to mankind’s advantage in a number of industrial processes. Primarily, biofilms help native bacteria do what they do best—grow and recycle all of the carbon and nutrients that other organisms produce, and provide humans with the type of environment to which we have become acclimated.
Here is biofilm in a stream in Yellowstone National Park. Biofilms can grow in all temperatures of water, from psychrophilic (cold) to thermophilic (hot) environments (courtesy of D. Davies, Center for Biofilm Engineering)
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Biofilms are responsible for tooth decay. Here is a photo showing the presence of a biofilm on human teeth. Human dental plaque has been exposed to a five percent sucrose (sugar) solution for five minutes, after which an iodine stain was applied. The sucrose solution was applied to the left central incisor (which appears on the right), while the right central incisor served as a control (photo courtesy of American Society for Microbiology)
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This microbial mat in a roadside puddle formed quickly during the height of summer in Pennsylvania. It demonstrates that it is not necessary to travel to exotic locations in order to study complex and interesting biofilm communities (photo courtesy of Biofilms: Online Manual, American Society for Microbiology)
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How Thick Are Biofilms?
A biofilm consisting of a single layer of bacteria (monolayer) may be as thin as one micron (10-6 m). However, such biofilms are rare. Even anaerobic biofilms will generally be several cells thick (several microns). Biofilms in oxygenated environments may be as thick as several centimeters (10-2 m). Microbial mats are specialized microbial communities composed mainly of photosynthetic bacteria. As the name suggests, these mats may become quite thick. |
Adverse Effects of Biofilms
Biofilms are responsible for diseases, such as otitis media, bacterial endocarditis (infection of the inner surface of the heart and its valves), cystic fibrosis and Legionnaire’s disease. They may be responsible for a wide variety of hospital-acquired infections, form the surfaces of catheters, medical implants, wound dressings, or other types of medical devices. They colonize household surfaces, including toilets, sinks, countertops and cutting boards. Poor disinfection practices and ineffective cleaning products may increase the incidence of illnesses associated with pathogenic organisms associated with normal household activity.
Biofilms are highly resistant to antibiotics. Consequently, very high and/or long-term doses are often required to eradicate biofilm-related infections.
Microbial biofilms on surfaces cost billions of dollars in each year in equipment damage, product contamination, energy losses and medical infections. For example, biofilms are notorious for causing pipe plugging, corrosion and water contamination. Biofilm contamination and fouling occurs in nearly every industrial-based process, including water treatment and distribution, pulp and paper manufacturing, and the operation of cooling towers.
Biofilms are responsible for diseases, such as otitis media, bacterial endocarditis (infection of the inner surface of the heart and its valves), cystic fibrosis and Legionnaire’s disease. They may be responsible for a wide variety of hospital-acquired infections, form the surfaces of catheters, medical implants, wound dressings, or other types of medical devices. They colonize household surfaces, including toilets, sinks, countertops and cutting boards. Poor disinfection practices and ineffective cleaning products may increase the incidence of illnesses associated with pathogenic organisms associated with normal household activity.
Biofilms are highly resistant to antibiotics. Consequently, very high and/or long-term doses are often required to eradicate biofilm-related infections.
Microbial biofilms on surfaces cost billions of dollars in each year in equipment damage, product contamination, energy losses and medical infections. For example, biofilms are notorious for causing pipe plugging, corrosion and water contamination. Biofilm contamination and fouling occurs in nearly every industrial-based process, including water treatment and distribution, pulp and paper manufacturing, and the operation of cooling towers.
Beneficial Aspects of Biofilms
Some reactors designed to promote biofilm growth [such as BioHaven matrix] are very effective for treating environmental wastes such as sewage, industrial waste streams or contaminated groundwater. Bacterial processes using both attached bacteria (biofilms) and suspended bacteria are the primary method for treating sewage. Biofilm reactors are also increasingly used to treat contaminants in water such as nitrate, perchlorate and methyl tertiary butyl ether (MTBE), because they completely degrade the contaminant and are usually cost-effective.
Biofilms attached to particles of contaminated soils and aquatic sediments help degrade soil-bound contaminants occurring from accidental chemical releases into the environment. This process is called in situ bioremediation, and has become an accepted and increasingly important method for cleaning up soils and groundwater contaminated from oil spills and other chemical releases.
Biofilms attached to plant roots - both floating and in-ground - help cycle nutrients to and from the plant, resulting in increased growth and productivity. One such plant microbe association is called the rhizosphere, and is a relationship between the plant roots/hairs and a complex microbial community. The rhizosphere association is mutualistic, meaning that it benefits both the bacteria and the plant. Plant roots secrete significant amounts of sugars, amino acids, vitamins and plant hormones, which vastly stimulate microbial growth in the immediate vicinity of the root. This relationship may also be important to the plant in that the microbial population may increase the nutrient absorption by the plant from the water or soil it grows in.
Several international research groups are dedicated to better understanding biofilms. These groups include:
• The Center for Biofilm Engineering, Montana State University
• The University of Calgary Biofilm Engineering Research Group (BERG)
Some reactors designed to promote biofilm growth [such as BioHaven matrix] are very effective for treating environmental wastes such as sewage, industrial waste streams or contaminated groundwater. Bacterial processes using both attached bacteria (biofilms) and suspended bacteria are the primary method for treating sewage. Biofilm reactors are also increasingly used to treat contaminants in water such as nitrate, perchlorate and methyl tertiary butyl ether (MTBE), because they completely degrade the contaminant and are usually cost-effective.
Biofilms attached to particles of contaminated soils and aquatic sediments help degrade soil-bound contaminants occurring from accidental chemical releases into the environment. This process is called in situ bioremediation, and has become an accepted and increasingly important method for cleaning up soils and groundwater contaminated from oil spills and other chemical releases.
Biofilms attached to plant roots - both floating and in-ground - help cycle nutrients to and from the plant, resulting in increased growth and productivity. One such plant microbe association is called the rhizosphere, and is a relationship between the plant roots/hairs and a complex microbial community. The rhizosphere association is mutualistic, meaning that it benefits both the bacteria and the plant. Plant roots secrete significant amounts of sugars, amino acids, vitamins and plant hormones, which vastly stimulate microbial growth in the immediate vicinity of the root. This relationship may also be important to the plant in that the microbial population may increase the nutrient absorption by the plant from the water or soil it grows in.
Several international research groups are dedicated to better understanding biofilms. These groups include:
• The Center for Biofilm Engineering, Montana State University
• The University of Calgary Biofilm Engineering Research Group (BERG)
Sources for More Information
A lot of information on biofilms is available through Internet sources, courses and textbooks. Good sources include:
• The Center for Biofilm Engineering
• Biofilms II: Process Analysis and Applications. J.D. Bryers, 2000.
• Microbial Biofilms. Lappin-Scott and Costerton, 1995.
• Structure and Function of Biofilms. W.G. Characklis, 1989.
• Biofilms: Recent Advances in Their Study and Control. L.V. Evans, 2000.
A lot of information on biofilms is available through Internet sources, courses and textbooks. Good sources include:
• The Center for Biofilm Engineering
• Biofilms II: Process Analysis and Applications. J.D. Bryers, 2000.
• Microbial Biofilms. Lappin-Scott and Costerton, 1995.
• Structure and Function of Biofilms. W.G. Characklis, 1989.
• Biofilms: Recent Advances in Their Study and Control. L.V. Evans, 2000.
How Do BioHavens And Biofilms Relate?
How Scientists Describe It
BioHaven matrix is a bio-reactor, a bio-reactive surface area for attachment of biofilms. Complex microbial communities (biofilm) also assemble on, and throughout, the root mass below the water surface, and contribute to water treatment processes through adhesion, filtration, nutrient uptake (direct use by plants), and sequestration (Bribie Island).
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A FTW [BioHaven Floating Island] consists of emergent wetland vegetation growing on a mat or structure floating on the surface of a pond-like water body. The plant stems remain above the water level, while their roots grow down through the buoyant structure and into the water column. In this way, the plants grow in a hydroponic manner, taking their nutrition directly from the water column in the absence of soil. Beneath the floating mat, a hanging network of roots, rhizomes and attached biofilms is formed. This hanging root-biofilm network provides a biologically active surface area for biochemical processes as well as physical processes such as filtering and entrapment. Thus, a general FTW design objective is to maximize the contact between the root-biofilm network and the polluted water passing through the system.
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The coverage of pond surface provided by the floating mat minimizes light penetration into the water column, thereby limiting the potential for algae growth. This will also have an impact on the composition of the biofilm community that develops within the network of roots under the floating mat. With the exception of the edges of the floating mats where there will be some light penetration, biofilms will be composed predominantly of non-photosynthetic bacterial communities. This will have an effect on the physico-chemical conditions that develop in the water column (e.g. dissolved oxygen and pH) and some of the biogeochemical processes affecting treatment within the FTW (e.g. the role played by algae in nutrient and element cycling).
Tanner & Headley 2008 11th International Conference on Wetland Systems for Water Pollution Control, in reference to the relatively large BioHaven in the Auckland field trial shown below.
Tanner & Headley 2008 11th International Conference on Wetland Systems for Water Pollution Control, in reference to the relatively large BioHaven in the Auckland field trial shown below.
Field trial in Auckland, NZ, conducted in 2013, to measure the effects of a BioHaven FTW on highway runoff compared to a control
The same island with mature plant growth
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The [2013] field trial undertaken in New Zealand suggested that the main factors contributing to the overall increased pond performance in presence of an FTW are as follows :
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More About Biofilm And BioHavens
We have coined the term "concentrated wetland effect" to describe the biofilm attachment surface provided by BioHaven matrix. Within one cubic foot of matrix there are 375 square feet of surface area. The fabrication and coatings that go into producing the matrix involve sophisticated engineering processes to make the surface area as resilient as the biofilms themselves.
Biofilm Reduces Microplastics
The BioHaven and hanging root-biofilm network provide a biologically active surface area for biochemical processes as well as physical processes such as filtering and entrapment. In other words, organic and inorganic particulates stick to the biofilm and are filtered out from the water column. This includes microplastics. BioHavens are part of the solution.
What Impact do Nanobubbles Have on Biofilms?
You may have read that nanobubbles are used in some industries to destroy pathogens. This is not the case in aquatic applications. The nanobubbles we disperse in water add dissolved oxygen quickly and support the aerobic bacteria that keep water healthy. They support removal of phosphorus, methane and the nitrification process. They also allow fish to thrive throughout the water column, and encourage the development of periphyton to revive the food web.
Do they inhibit denitrification? Our research shows that, once denitrifying bacteria are present, they are not inhibited by the presence of oxygen.
Do they inhibit denitrification? Our research shows that, once denitrifying bacteria are present, they are not inhibited by the presence of oxygen.
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In this extended interview with Erik van Lennep, Bruce Kania explores in depth the impact of biofilm in the natural context of pond management and lake stewardship (Designers of Paradise series).
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