THE PHYSIOLOGICAL-ACTIVITY OF BACTERIA ATTACHED TO SOLID-SURFACES

The chapter discusses the physiological activity of bacteria attached to solid surfaces. One of the most fundamental principles of microbial physiology is that cellular processes are influenced by environmental factors. The bacteria attached to surfaces often appear to differ physiologically from their freely suspended counterparts. Conditions at a solid surface can differ from those in the bulk phase, because of the special physical, chemical, and hydrodynamic characteristics of solid–liquid interfaces. The two most important features of the solid–liquid interface from the standpoint of an attached bacterium are —namely, (1) hydrodynamic conditions are different from the bulk phase and (2) there is a tendency for dissolved solutes and particles to be adsorbed at the surface. Together these factors affect concentration of substrates and the flux of nutrients and metabolic products between the interface and the bulk phase. The chapter presents the effects of surfaces on microbial activity in laboratory investigations. One of the most common ways of assessing activity has been measurement of assimilation of substrates such as low-molecular weight-organics like sugars, amino acids, and organic or fatty acids. There are numerous indications that immobilization on a surface offers the bacteria some protection from disadvantageous or potentially toxic conditions in the bulk phase. There are probably at least three reasons for such promotion of survival. First, the bacteria are often in microcolonies or biofilms, where the cells are embedded in a gel matrix, rather like a microbial “tissue”. This may foster homeostatic interactions among the various members of the biofilm community. Secondly, the biofilm polymers may help to protect cells by retarding penetration of biocides or antibiotics. Finally, it is also possible that intracellular homeostatic mechanisms are sometimes more effective for immobilized cells. © 1991 Academic Press Inc.