Light Acclimation of the Colonial Green Alga Botryococcus braunii Strain Showa

Abstract

In contrast to single cellular species, detailed information is lacking on the processes of photosynthetic acclimation for colonial algae, although these algae are important for biofuel production, ecosystem biodiversity, and wastewater treatment. To investigate differences between single cellular and colonial species, we studied the regulation of photosynthesis and photoprotection during photoacclimation for the colonial green alga Botryococcus braunii and made a comparison with the properties of the single cellular species Chlamydomonas reinhardtii. We show that B. braunii shares some highlight (HL) photoacclimation strategies with C. reinhardtii and other frequently studied green algae: decreased chlorophyll content, increased free carotenoid content, and increased nonphotochemical quenching (NPQ). Additionally, B. braunii has unique HL photoacclimation strategies, related to its colonial form: strong internal shading by an increase of the colony size and the accumulation of extracellular echinenone (a ketocarotenoid). HL colonies are larger and more spatially heterogenous than low-light colonies. Compared with surface cells, cells deeper inside the colony have increased pigmentation and larger photosystem II antenna size. The core of the largest of the HL colonies does not contain living cells. In contrast with C. reinhardtii, but similar to other biofilm-forming algae, NPQ capacity is substantial in low light. In HL, NPQ amplitude increases, but kinetics are unchanged. We discuss possible causes of the different acclimation responses of C. reinhardtii and B. braunii. Knowledge of the specific photoacclimation processes for this colonial green alga further extends the view of the diversity of photoacclimation strategies in photosynthetic organisms.

Large-scale screening of natural genetic resource in the hydrocarbon-producing microalga Botrycoccus braunii identified novel fast-growing strains

“…The increase in average colony size in culture is expected to increase the average amount of light received by the surface of a colony because of the reduction of self-shading among colonies 23 . Although the increase in colony size should decrease the amounts of light transmitted into the inner parts of a colony, cells placed in the inner parts of a colony are old and may have a limited physiological capacity to utilize strong light 36 . The OIT-678 strain formed a higher-density culture with a larger-sized colony than Showa (Fig.…”

The Loroxanthin cycle: A new type of xanthophyll cycle in green algae (Chlorophyta)

“…Loroxanthin is associated with the PSI and PSII supercomplexes of low light-grown C. reinhardtii (Pineau et al, 2001;Drop et al, 2011Drop et al, , 2014. Furthermore, Loroxanthin abundance and its ratio with Lutein vary in different light intensities in C. reinhardtii and other Chlorophyte (Bishop et al, 1989;Garrido et al, 2009;Bonente et al, 2012;van den Berg et al, 2019). We hypothesize that the differences in cellular Lutein and Loroxanthin content observed in low and high light grown cultures are due to a light-driven XC (Fig.…”

“…Loroxanthin, Neoxanthin , Violaxanthin and Chl b were separated according to an earlier described protocol (Pineau et al, 2001). Because with this method the separation between Chl a and Lutein could not be achieved on our column, Violaxanthin, Antheraxanthin , Zeaxanthin , Lutein, Chl b, Chl a and β-carotene were additionally separated using another protocol (van den Berg et al, 2019).…”

“…Loroxanthin is present in algae of the Chlorophyte, Euglenophyte and Chlorarachniophyte (Takaichi, 2011) and in addition to C. reinhardtii its content has been shown to fluctuate with the light intensity in the Chlorophytes Botryococcus braunii (van den Berg et al, 2019),…”

The Loroxanthin Cycle: A New Type of Xanthophyll Cycle in Green Algae (Chlorophyta)

“…Loroxanthin is associated with the PSI and PSII supercomplexes of low light-grown C. reinhardtii ( Pineau et al, 2001 ; Drop et al, 2011 , 2014 ). Furthermore, Loroxanthin abundance and its ratio with Lutein vary in different light intensities in C. reinhardtii and other Chlorophyte ( Bishop et al, 1989 ; Garrido et al, 2009 ; Bonente et al, 2012 ; van den Berg et al, 2019 ). We hypothesize that the differences in cellular Lutein and Loroxanthin content observed in low and HL grown cultures are due to a light-driven XC ( Figure 2A , spectra in Figure 2B ) that affects the Xanthophyll composition of the light-harvesting complexes and thereby their properties.…”