Ashner Prize
CHLORELLA OHADII - THE BUG THAT NEVER READ THE LITERATURE

With the premise that unique capabilities can be found in microorganisms facing extremely harsh conditions, we focused on those inhabiting desert biological sand crusts (BSC), one of the harshest environments to support life. Interestingly, working in the Negev desert, we have recently isolated a small green alga (that we named Chlorella ohadii), which does not conform to some of the basic dogmas in microbial ecology and photosynthesis:

1. Acquiring ability to acclimate to extreme environments is usually accompanied by reduced performance under optimal conditions. We showed that C. ohadii does not obey this rule. In its natural habitat, C. ohadii is facing frequent diurnal desiccation-hydration cycles, vast temperature amplitudes and extremely high illumination intensities (Treves et al. 2013; 2016). Nevertheless, we showed that when grown under optimal laboratory conditions it exhibits the fastest growth rates ever reported for an alga. When grown in photo-bioreactors under optimal conditions and continuous illumination, cells exhibit an ultradian growth rhythm, with alterations in O₂ and pH levels reflecting a metabolic shift during the growth of C. ohadii, and suggesting a role for metabolic regulation in its control ((Treves et al., in review).

2. Many years of intensive research provided us with basic understanding of the functioning of algal growth and the photosynthetic machinery. However, the unparalleled fast growth, extremely high photosynthetic rates and resistance to photodamage, suggest this we may still lack essential knowledge. We showed that C. ohadii is completely resistant to photoinhibition, does not suffer from photodamage and its productivity is unaffected by irradiances as high as twice full sun light and uncovered the mechanism involved (Treves et al. 2016, Chosen as Science Editor`s Choice, 18 March 2016, Vol. 351, issue 6279).

In view of the unparalleled growth and photosynthetic performance, C. ohadii may be used to clarify the processes that rate-limit growth and productivity of photosynthetic organisms. In an era when many are seeking for ways to increase biomass for food and energy production, the importance of these questions can`t be overestimated.