What are Biofilms?
Biofilms are collections of microorganisms and the extracellular polymers they secrete, attached to either inert or living substrata.
Microbiologists generally classify bacteria as planktonic (free floating) or sessile (anchored). In medicine, bacterial infections were traditionally considered to be planktonic, and antibiotics were developed with this in mind – it is relatively simple to kill planktonic bacteria. Bronchitis, for example, can be treated quickly and effectively with a course of antibiotics without harming the patient. But many infections are caused by sessile bacteria that form biofilms. An example of this is tuberculosis, in which biofilms of Mycobacterium tuberculosis infect the alveolar surfaces of the lung. Such organized biofilms harbor drug-tolerant cells and are notoriously hard to cure, requiring months or even years of treatment that can be as gruelling for the patient as it is for the infection.
Biofilms are capable of colonizing virtually any surface on earth and they are extremely difficult to kill. In industry, biofilms can be found adhering to surfaces in most aqueous environments, such as those of a pipeline wall or the tubes of a heat exchanger.
Biofilm formation begins when a single planktonic bacterium attaches to a surface by weak Van der Waals forces. As the now sessile bacterium grows and multiplies, it secretes a polysaccharide matrix that anchors it firmly to the substrate. In doing so it offers a more attractive adhesion site to passing bacteria and begins to engage in what is referred to as quorum sensing. This is essentially a means of communicating with planktonic bacteria through the transmission of biochemical messages that encourage them to join and help colonize the surface. Planktonic bacteria are able to assess the density of the transmitting population and are more inclined to join if they sense that the colony is strong.
Established biofilms consist of millions of cells in mats many thousands of layers deep, completely encased in a dense polysaccharide complex that renders them virtually impervious to antibiotics and chemical poisons (biocides). Mature biofilm formations behave like a single living organism, and may move collectively across a surface or detach themselves in clumps as a means to spread and colonize new surfaces.
Microbiologically Induced Pipeline Corrosion
Of particular concern to the oil and gas industry is a class of biofilm composed of one of the hundreds of species of Sulphate Reducing Bacteria (SRB). These biofilms interact with molecular hydrogen present on the surfaces of pipes and produce hydrogen sulfide as a by-product of metabolism. This process breaks down the iron and steel of even heavy-walled pipes, resulting in leaks and catastrophic pipeline failure. Other classes of biofilm can form thick plaques capable of plugging heat exchangers and valve bodies.
Characterizing a biofilm in its early stages allows us to devise a treatment for its eradication while protecting the environment through the responsible use of biocides. Monitoring and controlling biofilms in industry can prevent equipment failures, reduce environmental damage and minimize revenue loss.