Credit: BRANDX

The potential for developing commercially viable microbial H2 production systems as a renewable source of biofuel has been limited by the need for an anaerobic environment to enable photobiological H2 production in capable bacterial and algal species. Writing in Nature Communications, Bandyopadhyay et al. now show that the cyanobacterium Cyanothece sp. ATCC 51142 is capable of highly efficient H2 production under natural aerobic conditions.

Cyanothece sp. ATCC 51142 is a potentially viable system for producing biohydrogen as a renewable fuel source.

The marine bacterium Cyanothece sp. ATCC 51142 has a diurnal metabolic cycle: photosynthesis and carbon fixation occur during daylight hours, and then at night high rates of respiration create a suboxic intracellular environment that enables O2-sensitive processes, including N2 fixation and H2 production. The authors developed a two-stage approach to monitor H2 production by Cyanothece sp. ATCC 51142. In the first stage, they grew the bacteria aerobically in an alternating 12-hour light–dark cycle. A second 'incubation' stage was then carried out, in which the authors took cells from the end of a 12-hour light period and incubated them in air-tight vials for a further 12 hours under continuous illumination. Analysis of the head space at the top of the vial revealed high rates of H2 production (>150 μmol H2 per mg chlorophyll per hour) during this incubation period. Furthermore, the rate of H2 production could be enhanced by growing the cells with high levels of CO2 or glycerol.

The authors confirmed that H2 production was mediated by the nitrogenase system found in the bacterium. Interestingly, in the absence of molecular N2, nitrogenase systems channel all available electrons towards H2 production. Accordingly, when the authors incubated glycerol-supplemented Cyanothece sp. ATCC 51142 cells in the absence of N2, the rate of H2 production increased to up to 467 μmol H2 per mg chlorophyll per hour, which is an order of magnitude greater than the rates previously observed in other wild-type H2-producing model photosynthetic microorganisms under anaerobic conditions.

As glycerol and CO2 are both abundantly available as industrial waste products, the fact that they substantially enhance aerobic H2 production suggests that Cyanothece sp. ATCC 51142 is a potentially viable system for producing biohydrogen as a renewable fuel source.