Dunaliella salina (Chlorophyta) with small chlorophyll antenna sizes exhibit higher photosynthetic productivities and photon use efficiencies than normally pigmented cells

The photon use efficiencies and maximal rates of photosynthesis in Dunaliella salina (Chlorophyta) cultures acclimated to different light intensities were investigated. Batch cultures were grown to the mid-exponential phase under continuous low-light (LL: 100 mu mol photon m(-2) s(-1)) or high-light (HL: 2000 mu mol photon m(-2) s(-1)) conditions. Under LL, cells were normally pigmented (deep green) containing similar to 500 chlorophyll (Chl) molecules per photosystem II (PSII) unit and similar to 250 Chi molecules per photosystem I (PSI). HL-grown cells were yellow-green, contained only 60 Chi per PSII and 100 Chi per PSI and showed signs of chronic photoinhibition, i.e., accumulation of photodamaged PSII reaction centers in the chloroplast thylakoids. In LL-grown cells, photosynthesis saturated at similar to 200 mu mol photon m(-2) s(-1) with a rate (P-max) of similar to 100 mmol O-2 (mol Chl)(-1) s(-1). In HL-grown cells, photosynthesis saturated at much higher light intensities, i.e. - 2500 ymol photon m(-2) s(-1), and exhibited a three-fold higher P-max (similar to 300 mmol O-2 (mol Chi)(-1) s(-1)) than the normally pigmented LL-grown cells. Recovery of the HL-grown cells from photoinhibition, occurring prior to a light-harvesting Chi antenna size increase, enhanced P-max to similar to 675 mmol O-2 (mol Chi)(-1) s(-1). Extrapolation of these results to outdoor mass culture conditions suggested that algal strains with small Chi antenna size could exhibit 2-3 times higher productivities than currently achieved with normally pigmented cells.