Engineering photosynthetic light capture: impacts on improved solar energy to biomass conversion.
The main function of the photosynthetic process is to capture solar energy and to store it in the form of chemical 'fuels'. Increasingly, the photosynthetic machinery is being used for the production of biofuels such as bio-ethanol, biodiesel and bio-H2. Fuel production efficiency is directly dependent on the solar photon capture and conversion efficiency of the system. Green algae (e.g. Chlamydomonas reinhardtii) have evolved genetic strategies to assemble large light-harvesting antenna complexes (LHC) to maximize light capture under low-light conditions, with the downside that under high solar irradiance, most of the absorbed photons are wasted as fluorescence and heat to protect against photodamage. This limits the production process efficiency of mass culture. We applied RNAi technology to down-regulate the entire LHC gene family simultaneously to reduce energy losses by fluorescence and heat. The mutant Stm3LR3 had significantly reduced levels of LHCI and LHCII mRNAs and proteins while chlorophyll and pigment synthesis was functional. The grana were markedly less tightly stacked, consistent with the role of LHCII. Stm3LR3 also exhibited reduced levels of fluorescence, a higher photosynthetic quantum yield and a reduced sensitivity to photoinhibition, resulting in an increased efficiency of cell cultivation under elevated light conditions. Collectively, these properties offer three advantages in terms of algal bioreactor efficiency under natural high-light levels: (i) reduced fluorescence and LHC-dependent heat losses and thus increased photosynthetic efficiencies under high-light conditions; (ii) improved light penetration properties; and (iii) potentially reduced risk of oxidative photodamage of PSII.
Mussgnug
Jan H
JH
Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld 4072, Australia.
Thomas-Hall
Skye
S
Rupprecht
Jens
J
Foo
Alexander
A
Klassen
Viktor
V
McDowall
Alasdair
A
Schenk
Peer M
PM
Kruse
Olaf
O
Hankamer
Ben
B
D020418:Algal Proteins / Q000378:metabolism; D000818:Animals; D018533:Biomass; D049109:Cell Proliferation; D016825:Chlamydomonas reinhardtii / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D002734:Chlorophyll / Q000378:metabolism; D015536:Down-Regulation; D005453:Fluorescence; D005818:Genetic Engineering; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D010788:Photosynthesis / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D020524:Thylakoids / Q000648:ultrastructure
D020418:Algal Proteins; D045342:Light-Harvesting Protein Complexes; D012333:RNA, Messenger; D002734:Chlorophyll