Abstract
Photosynthetic microalgae have a high potential for the production of biofuels and highly valued metabolites. However, their current industrial exploitation is limited by a productivity in photobioreactors that is low compared to potential productivity. The high cell density and pigment content of the surface layers of photosynthetic microalgae result in absorption of excess photons and energy dissipation through non-photochemical quenching (NPQ). NPQ prevents photoinhibition, but its activation reduces the efficiency of photosynthetic energy conversion. In Chlamydomonas reinhardtii, NPQ is catalyzed by protein subunits encoded by three lhcsr (light harvesting complex stress related) genes. Here, we show that heat dissipation and biomass productivity depends on LHCSR protein accumulation. Indeed, algal strains lacking two lhcsr genes can grow in a wide range of light growth conditions without suffering from photoinhibition and are more productive than wild-type. Thus, the down-regulation of NPQ appears to be a suitable strategy for improving light use efficiency for biomass and biofuel production in microalgae.
Highlights
T content of the surface layers of photosynthetic microalgae result in absorption of excess photons and energy dissipation through non-photochemical quenching (NPQ)
The results showed that down-regulation of energy dissipation increases light use efficiency for biomass production, implying that this approach is a suitable strategy for
To better interpret these results, photon conversion efficiency (PCE) was plotted as a function of the percentage of reduction of maximal fluorescence (Supplementary Fig. S5B online) (Fm-Fm’)/Fm (%), Twhich yields a direct estimate of the proportion of excitation energy dissipated by NPQ processes
Summary
E Growth curves and productivity at different light regimes. The productivity of WT and npq[4] cells L was investigated by following growth in batch airlift photobioreactors at three different irradiances supplied as continuous or intermittent light, mimicking the effect of mixing cells through the steep light gradient in a dense culture (Table 1). Rand PCE for WT and the npq[4] mutant, whereas in the case of npq[4] lhcsr[1], the correlation diverged from the exponential fit, having a lower PCE than expected To better interpret these results, PCE was plotted as a function of the percentage of reduction of maximal fluorescence (Supplementary Fig. S5B online) (Fm-Fm’)/Fm (%), Twhich yields a direct estimate of the proportion of excitation energy dissipated by NPQ processes. The faster kinetics of growth and biomass production in the npq[4] mutant compared to WT is contradictory with previous reported results[17,24], in which the inhibition of growth in high light was observed in the absence of LHCSR3;. These results suggest that the availability of a higher level of excitation energy in npq[4] induced adaptive solutions, such as an increase in PSI and ATPase content to efficiently manage the higher amounts of electrons and protons transported by the thylakoid membranes
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