Before we delve into the life cycle of a biofilm, it's important to get a sense of what's usually found in these cell clusters. Microorganisms, or organisms too small to see with the naked eye, are the building blocks for biofilms. Different species of bacteria, protozoans, algae, yeasts and fungi can form biofilms. With most biofilms ranging from a few microns to hundreds of microns (one micron being one-millionth of a meter) in thickness, it's no wonder scientists prefer to use microscopes for the job.
So what's needed to start a biofilm?
Generally, all you need is a hydrated surface submerged in water or some other aqueous solution, microorganisms and favorable conditions. It's not that simple, though. Not all biofilms grow at the same rate or even require similar conditions to survive -- each type of microbe has its own needs. Still, there are some factors that can affect biofilm attachment and growth regardless of species:
- The availability of nutrients in the hydrated sample
- The physical and chemical characteristics of the surface, including its polarity
- The thickness of the conditioning layer, or material already attached to the surface
- pH levels
- The amount of shear, or rate of water flow, in the sample
- Antimicrobial levels in the sample
- The number of species in the sample
- Whether the microorganisms can move on their own
- The cellular structures of the microbe (appendages)
- The types of metabolic interactions between cells
Ultimately, it's essential to understand that microorganisms don't necessarily "think" while forming a biofilm; it just happens if the conditions are favorable. If a microbe is pushed by water flow or accidentally bumps into a surface, it may or may not attach the first time, or even at all for that matter. It's unclear what causes a cell to attach to a surface, and some researchers say a combination of factors -- including shear rates, electrostatic forces, conditioning layers (debris already on the surface) and nutrients available to the microorganism -- is more influential than a single factor [source: Sturman].
With microorganisms often at the mercy of their environments, it's amazing how something as small as a bacterium can hold on to a surface to settle in its new home.
Read on to understand why starting a biofilm is a slimy affair.