Production of H 2 by sulphur‐deprived cells of the unicellular cyanobacteria Gloeocapsa alpicola and Synechocystis sp. PCC 6803 during dark incubation with methane or at various extracellular pH

Aims:  To examine sulphur (S) deprivation in combination with the presence of methane (CH 4 ) and changes in extracellular pH as a method to enhance in situ hydrogen (H 2 ) generation during fermentation in the unicellular non‐diazotrophic cyanobacteria Gloeocapsa alpicola and Synechocystis PCC 6803. Methods and Results:  The level of H 2 production, measured using a gas chromatography, was determined in S‐deprived cells of G. alpicola and Synechocystis PCC 6803 during fermentation. Starvation on S enhanced the rate of H 2 production by more than fourfold in both strains. S‐deprived cyanobacteria were able to maintain maximum rate of H 2 production during at least 8 h of fermentation representing the entire dark period of a day. Increased H 2 production was observed during dark anoxic incubation with a gas phase of 100% CH 4 (up to four times) at lower pH of the medium (5·0–5·5). Conclusions:  S‐deprivation in combination with CH 4 , added or maybe produced by another micro‐organisms, and changes in the pH of the media can be used to further increase the specific capacity of unicellular non‐N 2 ‐fixing cyanobacteria to produce H 2 during fermentation with the overall aim of applying it for outdoor photobiological H 2 production. Significance and Impact of the Study:  S‐deprivation with respect to H 2 production is well studied in the green algae Chlamydomonas reinhardtii while its application for H 2 production in cyanobacteria is novel. Similarly, the stimulation of H 2 generation in the presence of CH 4 opens up new possibilities to increase the H 2 production. Natural gas enriched with H 2 seems to be a perspective fuel and may be an intermediate step on the pathway to the exploitation of pure biohydrogen.