Respiration, oxidative phosphorylation and yields in aerobic bacteria.

in effluent-treatment processes, the major concern is with biomass production, whereas in many microbial processes it is important to produce an extracellular product, e.g. amino acid, organic acid or polysaccharide. For microbial-product formation there must often be a diversion of energy, reductant and carbon away from biomass production into product formation, and a possible energy-dependent transport of the product out of the cell. These are largely unresearched areas, and although some of the rationale behind the production of ‘overflow’ metabolites is now understood (Neijssel & Tempest, 1975, 1976), little work has been done on the transport of compounds out of the microbial cell compared with the vast literature that exists on transport of compounds into the microbial cell. Finally, the projected use of entrapped microbial cells for chemical conversions has opened up a new area of microbial physiology concerned with carbon, energy and reductant flow in non-growing microbial cells. This is an area of great potential industrial interest and is in contrast to the many recent studies with growing and dividing cells in batch or continuous culture. This introduction is of necessity very sketchy and has not touched topics such as microbial photosynthesis or metal leaching, but these topics, as well as other areas of interest, will be discussed by the following speakers. I only wish to emphasize that the introduction of new microbial processes and the updating and refinement of traditional processes (Perlman, 1977, 1978) with modern process-control techniques and the use of immobilized or continuous cultures of microbial cells require a good basic knowledge of microbial physiology and growth energetics.