Photosynthesis and Hydrogen Production in Purple Non Sulfur Bacteria: Fundamental and Applied Aspects

Light-dependent hydrogen production by purple non sulfur bacteria (PNSB) has been studied for several decades. However the exact route that energy takes from the moment a photon is absorbed to the formation of a molecule of hydrogen is quite complex. The aim of this chapter is to review the researches carried out on the metabolic processes related to hydrogen production in PNSB, in particular stressing the issues related with the efficiency in the conversion of the energy deriving from the light in the energy-rich H2 molecule produced. The metabolic processes that bring form the light capturing to hydrogen production are described, with the relative bottlenecks and hurdles. The information currently available on the light distribution in various kind of photobioreactors are also reviewed, mainly focusing on the photosynthetic efficiency and on the efficiency in substrate conversion to H2 obtained in laboratory and outdoor experiments. From these data, it comes out how many different cellular processes can interact and affect photosynthetic efficiency and how complex is the route that brings from light energy to hydrogen energy.