Variation of the photosynthesis and respiration response of filamentous algae (Oedogonium) acclimated to averaged seasonal temperatures and light exposure levels

Filamentous algae (FA) have potential advantages over microalgae for wastewater treatment. However, their implementation at a large-scale is hindered by an inability to predict performance. This study compared the cellular responses (photosynthesis and respiration) and composition (pigments and photosystem proteins) of FA Oedogonium acclimatised to average summer and winter conditions (Melbourne, Australia). After seven days of acclimation the Chl a content of 'summer acclimated' (SA) algae was about half that of the 'winter acclimated' (WA) algae, which can be related to a cellular strategy to reduce photodamage under high light intensities. No statistically significant changes were observed in any identified proteins associated with photosystem PSII and the reaction centre of PSI. Transmission electron microscopy images revealed more prominent lipid bodies within the SA filaments than in WA filaments, but no discernible difference in the abundance of starch granules. Photosynthetic irradiance curves were compared for the SA and WA algae. Consistent with the differences in chlorophyll, the specific gross photosynthetic rate (μP, gross) was generally higher for the WA algae. The relative difference increased from around 2-fold at 15 °C to 3-fold at 25 °C, and then decreased to <1.5-fold at 30 °C and 35 °C. At all the tested temperatures, saturation irradiance levels were in the range of 75–500 μmol/m2·s. Photoinhibition was observed at 30 °C (above ~300 μmol/m2·s) and was more severe at 35 °C (above ~500 μmol/m2·s), with WA algae showing greater inhibition. In contrast, the respiration response was similar for the SA and WA algae. The study emphasises the significance of accounting for seasonal variations and their effects on biomass productivity and utilisation. The data obtained will enable the incorporation of acclimation and its effect on biochemistry and photosynthetic response into predictive models of FA performance in outdoor cultures.