INTERACTIONS BETWEEN BIOFILMS AND THE ENVIRONMENT

The surfaces of bacteria are highly interactive with their environment . Whether the bacterium is Gram-negative or Gram-positive, most surfac es are charged at neutral pH because of the ionization of the reactive chemical groups which stud them. Since prokaryotes have a high surfac e area-to-volume ratio, this can have surprising ramifications. For ex ample, many bacteria can concentrate dilute environmental metals on th eir surfaces and initiate the development of fine-grained minerals. In natural environments, it is not unusual to find such bacteria closely associated with the minerals which they have helped develop. Bacteria can be free-living (planktonic), but in most natural ecosystems they prefer to grow on interfaces as biofilms; supposedly to take advantage of the nutrient concentrative effect of the interface, although there must also be gained some protective value against predators and toxic agents. Using a Pseudomonas aeruginosa model system, we have determin ed that lipopolysaccharide is important in the initial attachment of t his Gram-negative,bacterium to interfaces and that this surface moiety subtly changes during biofilm formation. Using this same model system , we have also discovered that there is a natural tendency for Gram-ne gative bacteria to concentrate and package periplasmic components into membrane vesicles which bleb-off the surface. Since some of these com ponents (e.g., peptidoglycan hydrolases) can degrade other surrounding cells, the vesicles could be predatory; i.e., a natural system by whi ch neighboring bacteria are targeted and lysed, thereby liberating add itional nutrients to the microbial community. This obviously would be of benefit to vesicle-producing bacteria living in biofilms containing mixed microbial populations.