Many kinds of microorganisms produce hydrogen under favorable conditions. Biologically produced hydrogen, or biohydrogen in short, is attractive due to the mild operating conditions, as well as the potential of using renewable sources and nutrients such as sunlight and agricultural feedstock. The Biohydrogen Group of the Middle East Technical University investigates the conditions, methods and solutions to improve biohydrogen production in order to ultimately achieve a technically and economically feasible route for biohydrogen.

Among several paths to produce biohydrogen, our group focuses on biohydrogen using dark fermentative and photofermentative pathways. The present work illustrates highlights from studies directed to the latter pathway, i.e. photobiological hydrogen production using light energy and organic substrates. Purple non-sulfur bacteria (PNSB) are convenient microorganisms for this metabolic route, due to their versatile metabolism and ability to utilize a large portion of the solar spectrum.

Our work started more than 20 years ago with identifying favorable conditions for photofermentative hydrogen production using PNSB and understanding the basic metabolic routes involved. The potential for production using various nutrients, optimization of parameters such as the carbon-to-nitrogen ratio of the nutrients, and engineering of the bioreactors and the use of immobilization are mostly empirical approaches that we employed to enhance hydrogen production. Our studies of the genomic response of the bacteria to stimulants such as light and heat, and the investigation of the carbon fluxes in PNSB on the other hand, complemented our macroscopic experimental data by providing insight into the behavior of this bacteria. Examples from our recent results, based on work directed towards operational improvement and possible valorization of byproducts such as PHB, will be presented.