No Microbe is an Island: Biofilms
As I mentioned in my previous post, no microbe is an island, microbes are everywhere and will always be cohabitating with other microbes, be it with similar microbes as with a bacterium with a different species of bacterium, or with completely different microbes as with a bacterium and a virus. This is seen everywhere in our life filled world where different animals and life forms must live in the same habitat all the time.
The prevailing microbial lifestyle is for microbes to form biofilms. These are often composed of bacteria in a multispecies community, but can also be composed of other types of microbes. The bacterial biofilms are the most well known and studied, so in this post, from here on I will refer to the bacterial biofilm. In a biofilm, the bacteria will live together, stay or leave with purpose, communicate and share information in response to their environment and fill distinct niches within the community to the benefit of the bacteria involved. A biofilm is often compared to a city where people live in dense populations, share resources, communicate and have different jobs, all of which keep the city and its members functioning.
A biofilm is a microbial city, but to our naked eyes, these microscopic organisms appear as a coating or sludge when they are formed in a biofilm. Some biofilms include the plaque on our teeth, they are on the hulls of ships, on the inside of pipes, can form on indwelling devices in hospital patients and, of course, include pond scum on the surfaces of ponds such as on rocks. There are a huge number of different compositions of biofilms depending on the environment. One interesting example is the bacteria in a biofilm that developed a beneficial relationship with ants. This type of bacteria are called Actinobacteria, they are provided protection by the ants and in return will help maintain pathogen free fungal gardens for the ants (Currie 2001).
Figure 1: The highly structured biofilm formed by the bacteria Bacillus subtillus on the surface of a liquid in a beaker on the left and as a colony on the right.
The formation of a biofilm amongst bacteria is a complex series of events. First, the bacterium will slow down as it approaches a surface and it will form a transient association allowing it a chance to search for a place to settle down. Then, it will migrate to other bacteria and will form a more stable attachment to the surface amongst these other bacteria. This is when the bacteria form a very small colony or a microcolony to start the formation of the biofilm. This step in the process is likened to the bacterium choosing a neighbourhood in which to live. Finally, the buildings of the microbial city go up. These are made by the bacteria and are formed from complex sugars. The sugars making the buildings in the microbial cities are the reason why biofilms often seem slimy. Sugars allow for the retention of water. Once a biofilm is formed, bacteria may stay or leave according to their particular conditions. They may leave to start up other biofilms, or may even move within the biofilm much as commuters will amongst a city.
Figure 2: The formation of a biofilm. In the first cell the bacterium initially approaches a surface as a free swimming bacterium. Then, in the second cell, the bacterium slows its motility and forms a transient association with the surface. In the third cell, the bacterium will aggregate with other bacteria and form a microcolony. In the fourth cell, the bacteria form the biofilm structures from complex sugars they produce. In the final cell, a bacterium may detach from a biofilm to move and form other biofilms.
As I mentioned earlier, there are advantages for bacteria when in a biofilm. Since a biofilm constitutes a large number of bacteria and complex structures formed from sugars, biofilms offer protection and insulation from the environment. There is protection in numbers and in the biofilm structures. The structures will insulate the bacteria from getting swept away to a less favourable environment as well as prevent the diffusion of harmful substances to the bacteria from outside. For example, it is well known that bacteria in biofilms are more resistant to antibiotics, chlorine and detergents. Actually, many scientists believe that many of the antimicrobials such as antibiotics were made in response to the competition of microbes in the environment when they are amongst biofilms (Durrett and Levin, 1997). Antimicrobials prevent some microbes from entering or establishing a biofilm while giving the advantage to the microbes producing these products to colonize. As I mentioned before, in the microbial city of the biofilm, communication occurs frequently as with members of any city. This is no exception to the biofilm. Bacteria will “communicate” in response to their environment by means of producing molecules that will diffuse and be absorbed by other members of the biofilm, which will in turn affect bacterial activity. One example of this communication which I described in the previous blog post is how many bacteria will transfer a genetic trait responsible for conferring resistance to certain antibiotics to other bacteria which will not present this trait. This, in the end, will allow a formerly susceptible bacterium to become resistant to the antibiotic in question and the bacterium, in turn, can transfer the resistance trait to yet more bacteria. The transfer of antibiotic resistance is known to occur frequently in biofilms. This is yet another reason to limit the usage of antimicrobials since bacteria most often exist in biofilms. Also, antimicrobials most often act on replicating bacteria and since bacteria in biofilms share limited resources, they replicate less frequently, which is another limitation of the antimicrobial when acting on biofilms. In fact, some evidence indicates that using antimicrobials may even encourage the formation of biofilms in some instances (Hoffman et al. 2005).
Even if I did recommend the usage of antimicrobials for biofilms, they are not efficacious due to the nature of these structures. Biofilms, however, when seen in your pond, can be rather unsightly. So how does one deal with biofilms? Biofilms are structures that protect bacteria from the environment and help a bacterial colony adhere to a surface. Therefore, one of the ways to remove a biofilm is to remove the moisture and employ good old elbow grease to clean them off. Proper amounts of bleach and detergents must be used for proper amounts of time since bacteria in a biofilm tend to be harder to kill with these products (This will be elaborated in my next post “How to Properly Use a Cleaner”) This will ensure maximum results in combination with scrubbing. In the first post, there was mention of microbes, when left to their own devices, being able to form a proper ecosystem or environment in a pond. This applies to biofilms too, and we at Village Pond and Garden can help this along. We employ the use of probiotics to ensure proper microbial growth in a pond. That is, in order to limit the formation of biofilms and to ensure that bacteria better suited for the healthy ecology of a pond predominate in a biofilm that does form. We add beneficial bacteria to outnumber the bad ones and only certain sugars and metabolites that will ensure the growth of good bacteria in your pond.
• The prevailing lifestyle of microbes is to form biofilms. These are like microbial cities, but appear to us often as a slimy film.
• Biofilms are diverse and ubiquitous. They form on our teeth (plaque), on the hulls of ships, in pipes, on indwelling devices in hospital patients, and include pond scum.
• The formation of a biofilm is a complex series of events involving the aggregation of bacteria into microcolonies and the formation of the biofilm structures out of complex sugars.
• Biofilms offer many advantages to the microbes that comprise it. It offers protection from being swept away from the surface of attachment, and from harmful substances such as antibiotics, chlorine and detergents. Biofilms also offer the opportunity to exchange information with regards to its environment to assist in microbial adaptation.
• One such communication/transfer that takes place in biofilms is the transmission of traits responsible for antibiotic resistance. Therefore, the spread of antibiotic resistance can occur in biofilms.
• The best way to deal with biofilms is not to use antimicrobials but to employ the right amount of cleaner for the right amount of time. Probiotics are also useful because, by encouraging only the growth of some bacteria, they limit the formation of biofilms and ensure that the biofilms that do form are comprised of microbes that are good for your pond.
Currie CR. 2001. A community of ants, fungi, and bacteria: A multilateral approach to studying symbiosis. Annu Rev Microbiol 55: 357–380.
Durrett, R., and S. Levin. 1997. Allelopathy in spatially distributed populations. J. Theor. Biol. 185:165–171.
Kolter, R. 2010. Biofilms in lab and nature: a molecular geneticist’s voyage to microbial ecology. International Microbiology. 13:1-7.
Lopez, D., Vlamakis, H., and Kolter, R. 2010. Biofilms. Cold Springs Harbor Perspectives in Biology.
Watnick, P., and Kolter, R. Biofilm, City of Microbes. Journal of Bacteriology. 182(10):2675-2679.