Can Rose Bengal resilience be used as a marker for photosynthetic resilience of Nannochloropsis oceanica strains in excess light environments

Abstract Singlet oxygen (1O2) is an interesting candidate for study due to the widely held opinion that it plays a key role in photoinhibition of photo system II (PSII). Many studies have been conducted to elucidate the exact role of singlet oxygen (1O2) in photo-damage/repair, photoprotection, oxidative protection, and signaling. However, few studies have addressed the potential role of singlet oxygen as a marker for resilience to excess light environments. In the present study, we focus on the question of whether singlet oxygen resilience correlates with a strain's robustness in excess light environments. In order to address this question, two Nannochloropsis oceanica mutant strains, RB2 and RB113, both selected for heightened resilience to Rose Bengal (RB), a singlet oxygen (1O2) photosensitizer, were characterized. This included the characterization of the photosynthetic apparatuses and specific growth rate in relation to photosynthetic photon flux density (PPFD) in the growth media. Both of the RB resistant mutants showed higher photosynthetic capabilities when grown in high PPFD environments relative to the wild type (WT) strain. This was evident by higher photosynthetic capacity (namely 27% higher in the RB113 mutant and 94% higher in the RB2 mutant) relative to the WT strain when grown in an optimal temperature and an excess light environment (25 °C and 500 photons μmol s−1 m−2). In addition to the increase in photosynthetic capacity in the excess light environment of 25 °C and 500 photons μmol s−1 m−2, mutant strains also showed higher specific growth rates reflected by a 38% and 48% increase in the RB113 and RB2 mutant strains respectively. These results lead us to propose that Rose Bengal resilience in Nannochloropsis may serve as a marker for selecting species or strains better suited for growth in high light environments.