Final Scientific/Technical Report

Pakrasi, Himadri B.¹ 

[1] Washington University

关键词: CYANOBACTERIA;    HYDROGEN;    BIOFUELS;    PHOTOSYNTHESIS;    RESPIRATION Cyanobacteria;    hydrogen;    biofuel;    photosynthesis;    respiration;   

DOI  :  10.2172/1168828
RP-ID  :  DOE-WUSTL-64694
PID  :  OSTI ID: 1168828

美国|英语

来源: SciTech Connect

【 摘 要 】

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. In this project, we have shown that the cyanobacterium Cyanothece sp. ATCC 51142 has the capacity for highly efficient H2-production under natural aerobic conditions. The marine cyanobacterium 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 to occur, including N2-fixation and H2-production. We developed a two-stage approach to monitor H2-production by Cyanothece 51142. In the first stage, we grew the bacteria aerobically in an alternating 12 hour light/dark cycle. A second ???incubation??? stage was then carried out in which we took cells from the end of a 12 hour light growth period and incubated them in air-tight vials for a further 12 hours under continuous illumination. Analysis of the headspace in the vial revealed high specific rates of H2-production (>150 ??mol of H2 per mg chlorophyll per hour) during this incubation period. Furthermore, the rate of H2-production could be enhanced by growing the cells in the presence of high levels of CO2 or glycerol. We also confirmed that H2-production was mediated by the nitrogenase system found in these Cyanothece cells. Interestingly, in the absence of molecular N2, nitrogenase systems channel all available electrons towards H2-production. Accordingly, when we incubated glycerol-supplemented Cyanothece 51142 cells in the absence of N2, the rate of H2-production increased up to 467 ??mol of H2 per mg chlorophyll per hour, which is an order of magnitude greater than those 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 51142 is a potentially viable system for producing biohydrogen as a renewable fuel source. During this project, we have conducted a detailed systems level analysis of this interesting cyanobacterial system, and have created a rich knowledgebase for the use of Cyanothece cells as efficient biohydrogen producers in large scale.