Purple Bacteria: electron acceptors and donors

ABSTRACT: Purple bacteria form a heterogeneous group of microorganisms capable of growing under anoxic conditions by anoxygenic photosynthesis. They can be divided in purple non-sulfur bacteria, which are able to grow both phototrophically and in darkness, and purple sulfur bacteria, all of them capable to grow in the light but only few of them in the dark. They are characterized by a remarkable complexity in the metabolism, most of them being able to grow switching from chemotrophy to phototrophy, from organotrophy to litotrophy, from heterotrophy to autotrophy. In this article, the main electron acceptors and donors involved in the photosynthetic and in the respiratory electron transport chains are described, pointing out the crucial role of the quinone pool for the energetic processes in the cell.