Hydrogen in metabolism of purple bacteria and prospects of practical application

Purple bacteria are able to use H 2 for photoautotrophic, photomixotrophic, and chemoautotrophic growth, exhibiting high metabolic lability. Depending on the type of metabolism, hydrogen may be consumed with release of energy and/or reductive equivalents. Purple bacteria may also release H 2 as a terminal electron acceptor or in the course of dinitrogen fixation. Thus, hydrogen metabolism in purple bacteria is diverse; these bacteria are often used as models for investigation of the metabolic traits and interrelation of the metabolic pathways involving molecular hydrogen. In this review, the present-day state of investigation of hydrogen metabolism in purple bacteria is reflected and its possible practical applications are discussed. Nitrogenase and hydrogenase, the major key enzymes of hydrogen metabolism, are discussed in brief. A generalized scheme of H 2 role in the metabolism of purple bacteria is presented. Experimental approaches for investigation of the rates of hydrogen production are discussed. Immobilized systems are noted as the most promising approach for development of model systems for hydrogen production.