Biofilm is a complex community of microorganisms that attach to surfaces submerged in water. This natural phenomenon is widespread, occurring across diverse aquatic environments from natural streams to engineered water systems. Biofilm is often recognized as the slippery accumulation found on wet surfaces.
Understanding Biofilm
Biofilm is a structured community of microorganisms, including bacteria, fungi, algae, and protozoa, encased within a self-produced matrix. This matrix, known as extracellular polymeric substances (EPS), acts as a protective “slime” that adheres the microbial community to a surface. EPS primarily consists of polysaccharides, proteins, nucleic acids, and lipids, providing structural integrity and protecting the embedded cells. This protective layer also facilitates nutrient exchange and communication among the microorganisms.
The Formation Process
The development of biofilm typically occurs in several stages. It begins with the initial attachment of free-floating (planktonic) microorganisms to a submerged surface, a reversible process influenced by factors like surface properties, water conditions, and microbial motility. Subsequently, attached cells produce extracellular polymeric substances (EPS), leading to irreversible adhesion. As microorganisms reproduce and recruit other planktonic cells, the biofilm grows and matures into a complex, three-dimensional structure. Mature biofilms can then release new planktonic cells, capable of colonizing other surfaces and spreading.
Common Locations of Biofilm
Biofilm is ubiquitous in water environments, forming on various surfaces across both natural and human-made systems. In engineered settings, it commonly appears on the interior surfaces of water pipes, within water tanks, and on heat exchange equipment. Cooling towers and filtration systems also provide suitable environments. In residential contexts, biofilm can be found in showerheads, drains, and pet water bowls. Biofilms also naturally occur in aquatic environments, such as on stones in streambeds or within sediments in rivers and lakes.
Effects on Water Systems
Biofilms in water systems can lead to several impacts, particularly in engineered environments. Accumulation can reduce water flow in pipes and increase pressure within distribution systems. Biofilm also contributes to microbiologically influenced corrosion (MIC), damaging steel, copper, and galvanized pipes, which can lead to pinhole leaks and pipe blockages.
Biofilms serve as a protective niche for various microorganisms, including harmful pathogens. Pathogens like Legionella pneumophila (causing Legionnaires’ disease) and Escherichia coli can thrive within biofilms, becoming more resistant to disinfectants. This allows them to persist and potentially contaminate water supplies, posing public health risks. Biofilms can also cause aesthetic problems, leading to unpleasant tastes, odors, and discoloration of water. In natural environments, however, biofilms play beneficial roles in nutrient cycling and bioremediation, helping break down pollutants.
Strategies for Biofilm Control
Controlling biofilm in water systems often involves a combination of methods. Physical approaches include mechanical cleaning, such as scrubbing or high-pressure water jetting, to dislodge biofilm from surfaces. Regular flushing of water systems also helps prevent accumulation and remove loose biofilm. Ultrasonic cleaning, which uses high-frequency sound waves, can disrupt biofilm structures.
Chemical treatments use disinfectants like chlorine dioxide (ClO2) and other biocides to kill microorganisms within the biofilm matrix. Chlorine dioxide is effective as it can penetrate the biofilm and destabilize its structure. Biological strategies involve using enzymes to degrade the EPS matrix, making microbes more susceptible to disinfectants. Other advanced methods explore beneficial microorganisms or compounds that interfere with bacterial communication (quorum sensing inhibitors) to prevent biofilm formation.