ADHESION OF BACTERIA AND DIATOMS TO SURFACES IN THE SEA - A REVIEW

The initial event in biofilm formation on marine surfaces is the adsorption of an organic layer. This is followed usually by microorganisms and more developed forms, but there appears to be no obligatory order in this succession. The influence of the substratum chemistry on the rate and the extent of adhesion of microorganisms is still not fully agreed because many types of organisms in differing physiological states have been used, making consensus difficult. Sometimes the surface chemistry of the substratum was not established, which further clouds the picture. Genetic evidence now supports the idea that surface proximity promotes the induction of new metabolic capabilities in microorganisms, however the environmental signal responsible for this is not agreed. We propose that restricted diffusion at a surface plays a role in the process. Support for the hypothesis that the biofilm matrix polymers are not the adhesives involved in the initial attachment of cells to surfaces is growing. Diatom adhesion is a more complicated process than that for bacteria and requires glycoprotein and protein synthesis as well as metabolic energy, i.e. it is not a passive process. Bacteria can utilize surface-bound substrates and it is possible that diatoms attached to sediment grains can exploit their attached existence also by moving along concentration gradients of dissolved organic substances in adjacent pore waters. Practical interest in the adhesion of marine microorganisms derives from their role in the degradation of man-made structures. A film of organisms only a few microns in thickness causes the hydrodynamic drag on a ship to increase considerably. Investigations of the means by which marine microorganisms adhere to surfaces have been taking place for more that 50 yr, yet we still do not understand completely the mechanisms involved.