Pond slime is sometimes helpful, sometimes harmful. A research group at NUI Galway is exploring the finer points of bacterial biofilms. Dick Ahlstrom reports
Bacteria love company and if left to their own devices will happily form colonies that join together dozens of species. These colonies, also known as biofilms, are a scourge in medicine but have many useful applications in the treatment of polluted water.
"A biofilm is a slime of bacterial cells. They float around and when they find a suitable surface they stick and build colonies," explains Dr Vincent O'Flaherty who chairs a new interdisciplinary group at NUI Galway. The team includes seven academics and 50 postgraduate students working in two existing campus centres, the National Centre for Biomedical Engineering Science and the Environmental Change Institute.
He modelled the research cluster on a similar group in Montana. "The strength of our research is that it is multi-disciplinary, drawing on the expertise of scientists, clinicians and engineers," he says. "What we are finding is expertise in one area can be useful in another. It is the interaction of linkages and ideas."
Biofilms are made up of common bacteria that act in an unusual way when they join to form a film. "They behave very differently than non-attached microbes. They are actually quite organised colonies that can communicate and act like multicelled organisms."
A film typically would include a whole range of species collected together. "They can act cooperatively in that they can help one another, for example, break down food sources." Pebbles on a riverbed often form mats of slime and the plaque on your teeth is a similar collection of sticky microbes. "They are examples of biofilms," says O'Flaherty. Being able to stick to a surface is a key survival strategy for bacteria, he says. "If it finds itself in a nutrient-rich place it wants to put down roots and stick. Virtually all wild-type organisms will stick. When you bring them out of the wild and into the lab they tend to lose this characteristic."
This simple fact obscured the fact that bacteria living comfortable and stress-free lives in petrie dishes in the lab behaved differently from bacteria in the wild. For scientists to have ignored this property "has to have been one of the biggest mistakes that microbiology has made in 350 years", says O'Flaherty.
"One of the first things the bug does when it sticks is switch on a number of genes," he explains. It begins to express "extracellular polymeric substances", sticky, long chain sugar molecules. "That helps them stick and helps other organisms to stick and grow."
Biofilms can be harmful or helpful depending on their context, he says. They are a particular problem with any medical device implanted in a human from catheters and drips to artificial heart valves and joints. "Once you put an artificial surface in a human, bacteria find it very easy to attach to it."
The films grow rapidly in ideal conditions and cause serious infections. "For patients in intensive care, bacterial infection can be extremely dangerous and may even lead to death," says O'Flaherty. "It acts like a constant source of infection, seeding around the body." They are difficult infections to treat and also strongly resist treatment with antibiotics as the long chain sugar molecules protect the cells.
Biofilms have an upside, however, in waste water treatment. "The main advantages are because they are an immobilised bunch of cells you can get the cells to work for you," says O'Flaherty.
The main problem with waste water is dissolved organic material. "If you pass the waste water over a biofilm they sieve or filter the organic material from solution," he explains. The bacteria use the nutrients to grow and the water is left cleaner. "The bottom line is you get the biofilm to work for you to clean up the water."
The research team is looking into a wide range of targeted bacterial properties as a way to clean up foul water, pesticide residues, metal pollution and pharmaceutical waste streams. "Our approach is to select for a specific property", with bacteria chosen for the ability to lift out specific types of pollutants.
Nature tends to take care of its own, however, and a useful way to get the right collection of biofilm bacteria to grow is simply to give them time, space and food. You inoculate a gravel bed or trickle filter with a standard mix of bacteria but the colony that emerges will include species most suited to the waste material being treated. They will have an affinity for the most plentiful target pollutant.