Concentration dependent glycine effect on the photosynthetic growth and bio-hydrogen production by Rhodobacter sphaeroides from mineral springs

The effect of glycine as nitrogen source on growth and H2 production by purple non-sulfur bacterium Rhodobacter sphaeroides MDC 6521 (isolated from mineral springs in Armenia) in the presence of succinate as the carbon source was investigated. Growth rate, light absorption spectra, medium pH and oxidation-reduction potential (ORP) variation during bacterial anaerobic growth upon illumination were examined. At the presence of glycine the specific growth rate decreased significantly in comparison with control (∼25% for 5 mol m−3 or 7 mol m−3 glycine and ∼60% for 10 mol m−3 glycine). The culture initial pH 7.0 increased to ∼8.3, when 5 mol m−3 glycine was used. At the presence of 7 mol m−3 or 10 mol m−3 glycine pH was not changed much: pH raises to ∼7.6. ORP of R. sphaeroides gradually decreased to negative (−580 mV ± 20 mV) value during the growth at the presence of 5 mol m−3 glycine, indicating H2 production. 10 mol m−3 glycine did not provide H2 production (ORP decreased to −40 mV ± 5 mV). The results point out the concentration dependent glycine effect: 5 mol m−3 glycine can serve as nitrogen source for growth and H2 production by R. sphaeroides; however 10 mol m−3 glycine suppressed growth and H2 production. This might be applied when glycine or other amino acids are used as nitrogen sources in bio-hydrogen technology with photosynthetic bacteria.

► The results point out concentration dependent glycine effects on Rhodobacter sphaeroides.
► 5 mol m−3 glycine can serve as nitrogen source for growth and H2 production.
► 10 mol m−3 glycine suppressed growth and H2 production by R. sphaeroides.