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Abstract
Background: Purple non‑sulfur photosynthetic bacteria (PNSB) are among the potential bio‑hydrogen producers. PNSB can produce a higher hydrogen yield in comparison to dark fermentation by anaerobic bacteria. In this study, the detection of nifH and nifD by a polymerase chain reaction (PCR) assay was used to screen the potential photosynthetic bacteria capable of producing hydrogen from five different environmental sources. Since the efficiency of photo-hydrogen production is highly dependent on the culture conditions, initial pH, temperature and illumination intensity were optimized for maximal hydrogen production. The experiments were designed using response surface methodology (RSM) with central composite design (CCD).
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 (Hmax) and hydrogen production rate (Rm) from malic acid were an initial pH of 7.0, a temperature of 25.6ºC, and an illumination intensity of 2500 lux. Hmax and Rm levels of 1264 mL H2/l and 6.8 mL H2/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 lux gave the highest values of Hmax (1339 mL H2/l) and Rm (12.0 mL H2/l‑h) with a hydrogen yield and substrate conversion efficiency of 3.88 moL H2/moLmalate and 64.7%, respectively.
Conclusions: Rhodobacter sp. KKU-PS1 is an efficient bio-hydrogen producer capable of producing hydrogen from at least eight types of organic acids. A maximal hydrogen production by this strain was obtained by optimizing pH and temperature. Additionally, by optimizing the light intensity, Rm was increased by approximately two fold and the lag phase of hydrogen production was shortened.Upon acceptance of an article by the journal, authors will be asked to transfer the copyright to Electronic Journal of Biotechnology, which is committed to maintain the electronic access to the journal and to administer a policy of fair control and ensure the widest possible dissemination of the information. The author can use the article for academic purposes, stating clearly the following: "Published in Electronic Journal of Biotechnology at DOI:10.2225/volXX-issueX-fulltext-XX".
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