Comparative Physiology of Attached and Free-living Bacteria

Abstract

The environmental conditions at a solid-liquid interface differ from those in the bulk aqueous phase, and, accordingly, the physiological activity of bacteria attached to surfaces may differ from that of free living cells. There are three principal ways in which environmental conditions at a solid surface may influence the physiology of attached cells. First, nutrient concentration and/or accessibility may be different at the interface because of adsorption or irreversible binding of low molecular weight or macromolecular substrates. Second, processes, e.g., substrate transport and energy generation, which are sited in the cell membrane and which are central to all physiological processes, may be modified by elastic deformation of the cell envelope. Third, surfaces provide a site for colonization and the development of a bacterial biofilm, in which cells are embedded in a polymeric matrix. Such a colony microenvironment allows interactions between resident organisms, which frequently include a range of functional types, and affords protection from outside perturbations or lethal agents. Experimental measurements of the effects of solid surfaces on the activity of associated bacteria have varied considerably. The type of result obtained, ranging from promotion to inhibition of activity, has depended upon the type of activity measured, the organism, the substrate and/or its concentration, and the chemical composition of the substratum.