An Oak Ridge National Laboratory (ORNL) bioengineer has created designer transgenic algae that can photosynthetically produce hydrogen from water in a bioreactor much more efficiently than can wild algae.
Today's electrolytically produced hydrogen costs around $30 per million British thermal units (Btu); by comparison, natural gas costs about $3 per million Btu, and gasoline costs about $9 per million Btu. So the economic barriers to hydrogen production are formidable.
FIG. 1 illustrates an algal system for photosynthetic production of hydrogen (H2) from water using a wild-type alga such as Chlamydomonas reinhardtii.
Today's electrolytically produced hydrogen costs around $30 per million British thermal units (Btu); by comparison, natural gas costs about $3 per million Btu, and gasoline costs about $9 per million Btu. So the economic barriers to hydrogen production are formidable.
FIG. 1 illustrates an algal system for photosynthetic production of hydrogen (H2) from water using a wild-type alga such as Chlamydomonas reinhardtii.
ORNL bio-scientist James Weifu Lee (Knoxville, TN) manipulated the DNA of algae to design a switchable photosystem-II designer algae for photobiological hydrogen (H2) production. Lee also designed a photo-bioreactor and gas-product separation and utilization system to produce photobiological H2from the switchable PSII designer algae.
According to Lee in U.S. Patent 7,642,405, the designer algae and photobioreactor solve all the six major problems that currently challenge those in the field of photosynthetic hydrogen production.
The molecular structure (and thus the DNA sequence) of a polypeptide proton channel is designed according to certain natural proton-channel structures at nanometer scale. The designer transgenic algae includes at least two transgenes for enhanced photobiological H2 production wherein a first transgene serves as a genetic switch that can controls photosystem II (PSII) oxygen evolution and a second transgene encodes for creation of free proton channels in the algal photosynthetic membrane.
In one embodiment, the algae includes a DNA construct having polymerase chain reaction forward primer, a inducible promoter, a PSII-iRNA sequence, a terminator, and a PCR reverse primer. In other embodiments, the PSII-iRNA sequence is replaced with a CF1-iRNA sequence, a streptomycin-production gene, a targeting sequence followed by a proton-channel producing gene, or a PSII-producing gene.
The following lists the six technical problems that currently challenge researchers and investors in the field of photosynthetic H2 production and solved by Lee: (1) drainage of electrons by O2, (2) poisoning of the hydrogenase enzyme by O2, (3) the mixed H2 and O2 gas-product separation and safety issues, (4) restriction of photosynthetic H2 production by accumulation of a proton gradient, (5) competitive inhibition of photosynthetic H2 production by CO2, and (6) requirement for bicarbonate binding at photosystem II (PSII) for efficient photosynthetic activity.
In wild-type algae as illustrated in FIG. 1, photosynthetic water splitting under anaerobic condition can result in simultaneous production of H2 and O2 in the same cell. Therefore, the gas products in this case are a dangerous mixture of H2 and O2 that requires safe separation (problem 3). Furthermore, the O2 produced in the alga can inhibit H2 production by two mechanisms: acting as an electron acceptor [possibly through the RuBisco (which is also a known oxygenase) enzyme at the Calvin cycle] that drains the electrons away from the Fd/hydrogenase H2 production pathway (problem 1), and poisoning the hydrogenase enzyme directly (problem 2).
Incorporation of a proton channel helps eliminate the four proton-gradient-related problems (1, 4, 5, and 6), while use of the switchable PSII solves the three O2-related problems (1, 2, 3). Therefore, the combination of a switchable PSII with a proton channel in the switchable PSII designer alga (FIGS. 4B and 4C) ensures to solve all the six technical problems that currently challenge those in the field of photobiological H2 production: (1) drainage of electrons by O2, (2) poisoning of the hydrogenase enzyme by O2, (3) the mixed H2 and O2 gas-product separation and safety issues, (4) restriction of photosynthetic H2 production by accumulation of a proton gradient, (5) competitive inhibition of photosynthetic H2 production by CO2, and (6) requirement for bicarbonate binding at photosystem II (PSII) for efficient photosynthetic activity.
FIG. 4B illustrates the photobiological H2 production pathway in a switchable-PSII designer alga when the designer PSII-iRNA (and/or PSII-inhibitor such as streptomycin) gene and the designer CF1-iRNA gene are expressed upon induction of the hydrogenase.
Incorporation of a proton channel helps eliminate the four proton-gradient-related problems (1, 4, 5, and 6), while use of the switchable PSII solves the three O2-related problems (1, 2, 3). Therefore, the combination of a switchable PSII with a proton channel in the switchable PSII designer alga (FIGS. 4B and 4C) ensures to solve all the six technical problems that currently challenge those in the field of photobiological H2 production: (1) drainage of electrons by O2, (2) poisoning of the hydrogenase enzyme by O2, (3) the mixed H2 and O2 gas-product separation and safety issues, (4) restriction of photosynthetic H2 production by accumulation of a proton gradient, (5) competitive inhibition of photosynthetic H2 production by CO2, and (6) requirement for bicarbonate binding at photosystem II (PSII) for efficient photosynthetic activity.
FIG. 4B illustrates the photobiological H2 production pathway in a switchable-PSII designer alga when the designer PSII-iRNA (and/or PSII-inhibitor such as streptomycin) gene and the designer CF1-iRNA gene are expressed upon induction of the hydrogenase.
FIG. 4C illustrates the photobiological H.sub.2 production pathway in a switchable-PSII designer alga when the designer PSII-suppressor (and/or inhibitor) gene and the designer proton-channel producing gene are expressed upon induction of the hydrogenase; and
FIG. 5 illustrates one embodiment of a photo-bioreactor and gas-product separation and utilization system.
The CO2 and H2 produced in the anaerobic reactor 506 are pulled through a H2 separation membrane 510 by a vacuum pump 508. The CO2 on one side of the membrane 510 is transferred to the aerobic reactor 502 via line 522. The H2 on the opposite side of the membrane 510 is transferred to a H2 storage tank 512 and the fuel cell 514.
The algal culture 518 in the anaerobic reactor 506 is transferred to the aerobic reactor 502 via line 526 when the algal culture 518 is exhausted. The algal culture 520 in the aerobic reactor 502 is transferred to the anaerobic reactor 506 via line 524 when the algal culture 520 is ready for H2 production.
