Modulation of Cyclic Electron Flow and Light-Harvesting Antenna to Enhance Light Energy Utilization in Nannochloropsis oceanica

One of the major challenges the world has to face is the increasing population, which leads to higher energy and food demand. Meanwhile, in order to avoid fossil resource consumption and arable land exploitation from worsening further, a real energy transition is required. The usage of the microalgae represents a sustainable solution that can contribute to biomass and bioproducts production, thanks to microalgae’s growth rate, carbon capture capacity, and the lack of competition with food crops for arable land. However, microalgae’s potential is markedly reduced due to biomass yield under large-scale cultivation. Nannochloropsis oceanica is a microalga with promising industrial applications, but its large-scale productivity is constrained by sensitivity to light fluctuations and by inhomogeneous light distribution over the high-density culture. To solve these limitations, in this work it is proposed a biotechnological approach which targets two photoprotection mechanisms: the cyclic electron flow (CEF), which play a role in relieving the risk of over-reduction in the photosystem I (PSI) and the Non photochemical quenching (NPQ) mediated by xanthophyll cycle, which is responsible for the dissipation of excess of energy absorbed. In the first case, the aim was to verify the role of PGR5/PGRL1 driven CEF in N. oceanica to assess its impact on biomass productivity, by characterizing strains overexpressing or depleted of PGR5 and PGRL1. The second strategy involved the combination of two already validated approaches: the optimization of NPQ kinetics and the reduction of chlorophyll content. To combine the two, parental strains overexpressing the enzymes involved in the xanthophyll cycle. The latter were mutagenized via random mutagenesis with the aim of generating truncated light antennas (TLA) strains and improving the light distribution in photobioreactors.