Marine bacterial fouling: A scanning electron microscope study

Abstract

A range of substrates has been examined in order to determine the types of attachment mechanism employed by marine bacteria. Use of the scanning electron microscope (SEM) has also allowed an investigation of the initimate relationship between an antifouling paint matrix and its attached bacterial community. Plastic (Thermanox) and glass coverslips, together with Cu2O-based and TPTF-based antifouling paints and their respective empty-matrix analogues have been used in this study. Observations over periods of up to 4 wk have shown that extensive bacterial communities can develop. A variety of bacteria have been found: cocci; various rods; stalked forms; and prosthecate types. These bacteria also exhibit a range of attachment mechanisms. Initial attachment is by simple stickiness of cell walls, flagella, pili (fimbriae) or stalks. This stickiness can be attributed to an actual adhesive, electrostatic forces, electrical double-layer phenomena or to London/van der Waals forces. Often, attachment is subsequently improved by the secretion of insoluble, high molecular weight, polysaccharidic material. This material is found in the form of strands, pads, sheets or capsules and acts to bridge the space between the cell wall and substrate or adjacent cells. Thus, stalked forms are found attached by basal pads of mucilage whilst cocci and rods are often found enmeshed in mucilage strands and sheets, but less often attached by pads and capsules. Initially, single bacterial cells attach and give rise to colonies by cell division. Continuing growth of adjacent colonies leads to the development of confluent films over the substrate surface. Further growth results in thickening until eventually the entire surface is coated with a dense community of mixed bacteria together with their adhesive mucilage. In the case of antifouling paints, the porous nature of the matrix allows invasion by bacteria and the possibility of pore blockage by adhesive polysaccharides. This problem is discussed with reference to the paint's loss of antifouling efficiency.