The Effect of Solid Surfaces upon Bacterial Activity

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Abstract
Solid surfaces promote the growth of bacteria in dilute nutrient solns. Minute but demonstrable quantities of organic nutrients are adsorbed on glass surfaces in sea water. The organic nutrients enhance bacterial activity. Many bacteria found in the sea are sessile, growing exclusively or preferentially attached to a solid surface. Most of the sessile bacteria appear to exude a mucilaginous holdfast. A few have stalks. The beneficial effect of solid surfaces is most evident in solns. having a nutrient conc. of < 10 mgm./l. Besides concentrating nutrients by adsorption and providing a resting place for sessile bacteria, solid surfaces apparently retard the diffusion of exoenzymes and hydrolyzates away from the cell, thereby promoting the assimilation of nutrients which must be hydrolyzed extracellularly prior to ingestion. To be most effective, the solid surface must be distributed throughout the dilute nutrient soln. Glass, plastics, porcelain, sand, kieselguhr and other inert particulate materials are beneficial. To be beneficial the surface area must be larger than the bacteria; particles smaller than bacteria sometimes are harmful. Hydrophobic or non-wettable surfaces are less beneficial than hydrophilic ones. Positively charged surfaces promote the attachment of bacteria. Neither color, plane nor the degree of smoothness of a surface seems to influence the attachment of bacteria.

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