Abstract Hydrogen is the fuel for the future, mainly due to its recyclability and nonpolluting nature. Bio- logical hydrogen production processes are operated at ambient temperature and atmospheric pressures, thus are less energy intensive and more environmentally friendly as compared to thermochemical and electro- chemical processes. Biohydrogen processes can be broadly classified as: photofermentation and dark fer- mentation. Two enzymes namely, nitrogenase and hydrogenase play an important role in biohydrogen production. Photofermentation by Purple Non-Sulfur bacteria (PNS) is a major field of research through which the overall yield for biological hydrogen pro- duction can be improved significantly by optimization of growth conditions and immobilization of active cells. The purpose of this paper is to review various pro- cesses of biohydrogen production using PNS bacteria along with several current developments. However, suitable process parameters such as carbon and nitro- gen ratio, illumination intensity, bioreactor configura- tion and inoculum age may lead to higher yields of hydrogen generation using PNS bacteria. Keywords Purple non-sulfur (PNS) bacteria Biohydrogen Photofermentation Bioreactor Nitrogenase Hydrogenase Nomenclature B.C.-I Bacteriochlorophyll-I Cyt Cytochrome E eff Efficiency of light energy conversion (%) Fd (ox) Ferredoxin (oxidized form) Fd (red) Ferredoxin (reduced form) DG o ¢ Gibb’s free energy (kJ mol –1 ) k c Apparent specific growth rate (h –1 ) LH-I Light harvesting I antenna complex MSW Municipal solid wastes PVA Polyvinyl alcohol RC Reaction center t Time (h) x Cell dry mass conc (g l –1 ) dx/dt Rate of change of cell dry mass conc (g l –1 h –1 ) x max Maximum cell dry mass conc (g l –1 ) Greek letters l Specific growth rate (h –1 ) l e Specific growth rate constant in exponential phase (h –1 ) Introduction In the present global scenario, the utilization of fossil fuels as major sources of energy (about 80% of the present demand) is reducing the fossil energy re- sources day by day. Hydrogen gas is considered as a future energy carrier by virtue of the fact that it is renewable and does not cause the ‘‘greenhouse N. Basak (&) Department of Leather Technology, Dr. B. R. Ambedkar National Institute of Technology, Jalandhar 144011, Punjab, India e-mail: basakn812@yahoo.com D. Das N. Basak Department of Biotechnology, Indian Institute of Technology, Kharagpur 721302, India 123 The prospect of purple non-sulfur (PNS) photosynthetic bacteria for hydrogen production: the present state of the art Nitai Basak Debabrata Das Received: 22 April 2005 / Accepted: 21 April 2006 / Published online: 18 June 2006 Ó Springer Science+Business Media B.V. 2006