Background: In this study, the detection of nifH and nifD by a polymerase chain reaction assaywas used to screen
the potential photosynthetic bacteria capable of producing hydrogen from five different environmental sources.
Efficiency of photo-hydrogen production is highly dependent on the culture conditions. Initial pH, temperature
and illumination intensity were optimized for maximal hydrogen production using response surface
methodology with central composite design.
Results: Rhodobacter
sp. KKU-PS1 (GenBank Accession No. KC478552) was isolated from the methane
fermentation broth of an UASB reactor. Malic acid was the favored carbon source while Na-glutamate was the
best nitrogen source. The optimum conditions for simultaneously maximizing the cumulative hydrogen
production (H
max) and hydrogen production rate (R
m) from malic acid were an initial of pH 7.0, a temperature
of 25.6°C, and an illumination intensity of 2500 lx. H
max and R
m levels of 1264 ml H
2/l and 6.8 ml H
2/L-h
were obtained, respectively. The optimum initial pH and temperature were further used to optimize the
illumination intensity for hydrogen production. An illumination intensity of 7500 lx gave the highest values of
H
max (1339 ml H
2/l) and R
m (12.0 ml H
2/L-h) with a hydrogen yield and substrate conversion efficiency of
3.88 mol H
2/mol
malate and 64.7%, respectively.
Conclusions: KKU-PS1 can produce hydrogen from at least 8 types of organic acids. By optimizing pH and
temperature, a maximal hydrogen production by this strain was obtained. Additionally, by optimizing the light
intensity, R
m was increased by approximately two fold and the lag phase of hydrogen productionwas shortened.
