Microaerobic dark fermentative hydrogen production by the photosynthetic bacterium, Rhodobacter capsulatus JP91

Abstract

The photosynthetic bacterium Rhodobacter capsulatus produces hydrogen under nitrogen-limited, anaerobic, photosynthetic conditions. The present study examined whether R. capsulatus can produce hydrogen under microaerobic conditions in the dark with limiting amounts of O2 and fixed nitrogen. The relationship between hydrogen production, different O2 concentrations and carbon sources as well as two different N sources, glutamate and ammonium, were studied in batch culture using a Hup strain of R. capsulatus. The effect of different O2 concentrations, ranging from 0.5 to 20%, on hydrogen production was examirrelated (r2 = -0.3). Succinate (25 mM) together with glutamate (3.5 mM) gave the highned in dark batch cultures of R. capsulatus grown on RCV medium. Different carbon sources, e.g. glucose, succinate, lactate, acetate and malate, were used at various concentrations (20-40 mM). Similarly, different concentrations of glutamate and ammonium (2-9 mM) were examined for optimum microaerobic dark hydrogen production. Maximum hydrogen production was observed at an O2 concentration of 4-8%. There was a highly positive correlation between O2 and growth (r2 = 0.67), whereas O2 concentration and hydrogen productivity were negatively coest specific hydrogen productivity [5.61 μmol hydrogen/(mg cell dry weight/ml)]. The maximum average hydrogen yield was 0.6 mol hydrogen/mol malate followed by 0.41 mol hydrogen/mol lactate, 0.36 mol hydrogen/mol succinate, whereas minimum amounts of hydrogen were produced from glucose and acetate (0.16 mol hydrogen/mol and 0.07 mol hydrogen/mol, respectively). The implications for developing a system capable of improved hydrogen production are discussed. © The Author 2012. Published by Oxford University Press. All rights reserved.