Investigation of the photorespiratory pathway in the seawater microalga Nannochloropsis

The current global production system for essential goods relies primarily on non-renewable, polluting energy sources, driving environmental issues like climate change. In this context, sustainable biomass sources offer a viable alternative, with microalgae standing out for their extraordinary production of valuable molecules attractive for many areas of the economy. Among microalgae, Nannochloropsis species draw a lot of attention due to their ability to produce significant amounts of commercially relevant compounds, such as carotenoids, omega-3 fatty acids, chlorophylls and triacylglycerols. However, Nannochloropsis potential is currently not fully exploited due to significantly higher costs and lower yields compared to fossil fuel-based processes. Additionally, photosynthetic efficiency is often hindered by several factors, making it a key target for the biotechnological improvement of microalgae. Photorespiration, for example, plays a role in preventing the accumulation of a toxic compound, the 2-phosphoglycolate, that derives from the oxygenic reaction of RuBisCO, but such a process is energy demanding and releases previously fixed carbon dioxide, limiting photosynthetic efficiency. Therefore, it also represents a limitation for the generation of biomass, whose implications for algae industrial productivity are still unclear. Here is presented a genetic engineering approach for the investigation of the impact of photorespiration in Nannochloropsis, whereby CRISPR-Cpf1 technology is used to knock-out (KO) the gene coding for glycolate oxidase (GOX), catalyzing an essential enzymatic step of the pathway. Hence, in this study both the growth and photosynthetic efficiency of Nannochloropsis GOX KO strains were investigated upon exposure to different environmental conditions. Since photorespiration turned out to have an impact on both growth and photosynthetic performance of Nannochloropsis, the second part of this project has been to bypass photorespiration itself by developing an optimized metabolic pathway, with the objective to increase biomass productivity upon industrial microalgae cultivation.

The current global production system for essential goods relies primarily on non-renewable, polluting energy sources, driving environmental issues like climate change. In this context, sustainable biomass sources offer a viable alternative, with microalgae standing out for their extraordinary production of valuable molecules attractive for many areas of the economy. Among microalgae, Nannochloropsis species draw a lot of attention due to their ability to produce significant amounts of commercially relevant compounds, such as carotenoids, omega-3 fatty acids, chlorophylls and triacylglycerols. However, Nannochloropsis potential is currently not fully exploited due to significantly higher costs and lower yields compared to fossil fuel-based processes. Additionally, photosynthetic efficiency is often hindered by several factors, making it a key target for the biotechnological improvement of microalgae. Photorespiration, for example, plays a role in preventing the accumulation of a toxic compound, the 2-phosphoglycolate, that derives from the oxygenic reaction of RuBisCO, but such a process is energy demanding and releases previously fixed carbon dioxide, limiting photosynthetic efficiency. Therefore, it also represents a limitation for the generation of biomass, whose implications for algae industrial productivity are still unclear. Here is presented a genetic engineering approach for the investigation of the impact of photorespiration in Nannochloropsis, whereby CRISPR-Cpf1 technology is used to knock-out (KO) the gene coding for glycolate oxidase (GOX), catalyzing an essential enzymatic step of the pathway. Hence, in this study both the growth and photosynthetic efficiency of Nannochloropsis GOX KO strains were investigated upon exposure to different environmental conditions. Since photorespiration turned out to have an impact on both growth and photosynthetic performance of Nannochloropsis, the second part of this project has been to bypass photorespiration itself by developing an optimized metabolic pathway, with the objective to increase biomass productivity upon industrial microalgae cultivation. Here is presented a genetic engineering approach for the investigation of the impact of photorespiration in Nannochloropsis, whereby CRISPR-Cpf1 technology is used to knock-out (KO) the gene coding for glycolate oxidase (GOX), catalyzing the third enzymatic step of the pathway. Hence, in this study both the growth and photosynthetic efficiency of Nannochloropsis GOX KO strains were investigated upon exposure to different environmental conditions. In addition, if photorespiration turned out to be active in Nannochloropsis, the second part of this project would be to bypass photorespiration itself by developing an optimized metabolic pathway, with the objective to increase biomass productivity upon industrial microalgae cultivation.