Even soil microorganisms effectively live in water, although this may be as little as a film of water. A large proportion of microorganisms occur in microenvironments and in biofilms. Microorganisms distribute themselves in the appropriate pocket as dictated by their physiological requirements. The anaerobic center is colonized by obligate anaerobes. The aerobic surface is colonized by obligate aerobes.
Facultative aerobes appear throughout the particle.
Biofilms Biofilms are habitats consisting of layers of slime containing excreted polysaccharides. Examples include rocks in rivers and teeth. Allows microorganisms to aggregate. Plaque on teeth is actually a biofilm where bacteria live. Cavities in teeth are the result of attack by lactic acid produced via fermentation by Streptococcus bacteria that live in the teeth biofilm.