The Energy Flow in Bacteria: The Main Free Energy Intermediates and Their Regulatory Role

Bacteria require for growth and survival chemical free energy, which is derived from catabolic substrates. In phototrophic bacteria light energy can be the main source of this chemical free energy. The energy supplied by these energy sources is usually not directly applied for the synthesis of cell material, or for other energy requiring processes, but is first translated into other forms of metabolic energy. Generally, three main types of “metabolic energy intermediates” can be distinguished. With these energy intermediates, energy-requiring metabolic processes can be driven and/or the energy can be transduced into other energy intermediates. These three main metabolic energy intermediates are phosphorylation potentials, redox potentials, and transmembrane (e1ectro)chemical potentials. The important role of transmembrane electrochemical potentials is to serve as metabolic energy intermediates. This chapter discusses the current notion of energy flow in bacteria with special emphasis on the regulation exerted by the components of the three main free energy intermediates on the microbe's metabolism.