The mechanisms whereby the green alga Chlorella ohadii, isolated from desert soil crust, exhibits unparalleled photodamage resistance

Abstract

SummaryExcess illumination damages the photosynthetic apparatus with severe implications with regard to plant productivity. Unlike model organisms, the growth of Chlorella ohadii, isolated from desert soil crust, remains unchanged and photosynthetic O 2 evolution increases, even when exposed to irradiation twice that of maximal sunlight.Spectroscopic, biochemical and molecular approaches were applied to uncover the mechanisms involved.D1 protein in photosystem II (PSII) is barely degraded, even when exposed to antibiotics that prevent its replenishment. Measurements of various PSII parameters indicate that this complex functions differently from that in model organisms and suggest that C. ohadii activates a nonradiative electron recombination route which minimizes singlet oxygen formation and the resulting photoinhibition. The light-harvesting antenna is very small and carotene composition is hardly affected by excess illumination. Instead of succumbing to photodamage, C. ohadii activates additional means to dissipate excess light energy. It undergoes major structural, compositional and physiological changes, leading to a large rise in photosynthetic rate, lipids and carbohydrate content and inorganic carbon cycling.The ability of C. ohadii to avoid photodamage relies on a modified function of PSII and the dissipation of excess reductants downstream of the photosynthetic reaction centers. The biotechnological potential as a gene source for crop plant improvement is self-evident.

Oxygen and ROS in Photosynthesis

“…Further indirect evidence on the participation of 1 O 2 in photoinhibition of PSII also varies, as the modification of the recombination reactions of PSII toward non-1 O 2 -producing direction provides protection against photoinhibition [326], whereas the protection offered by NPQ is very limited [327], suggesting that the photoinhibition of PSII may not depend only on the excitation of Chl [320,328]. The photoinhibition-tolerant green alga Chlorella ohadii exhibits a recombination reaction model that is expected to lead to low 1 O 2 production [329].…”

Potential and Challenges of Improving Photosynthesis in Algae

“…Alternatively to genetic engineering and mutation/phenotypic selection, an alternative approach consists into sampling and evaluating algal biodiversity, particularly in extreme environments which might provide interesting performance when such strains are grown in optimal conditions. An example of this is the case of Chlorella ohadii, a chlorella strain from the Sinai desert, which was reported to exhibit high productivity and the robustness of growth [94,95].…”

The acclimation of Chlorella to high-level nitrite for potential application in biological NOx removal from industrial flue gases

“…have been proved to be a good option for biodiesel production Mata et al, 2010;O'Grady and Morgan, 2011). Furthermore, a very recently discovered species of Chlorella, Chlorella ohadii (Treves et al, 2016), has been shown to have a growth potential and a tolerance to high irradiance extraordinary for eukaryotes, which may immensely increase the biomass productivity of an algal production plant. Unfortunately, this strain is not easily available at the moment and research on its application potential is therefore somewhat problematic.…”