Effects of irradiance, temperature, nutrients, and pCO2 on the growth and biochemical composition of cultivated Ulva fenestrata

Abstract

Ulva fenestrata is an economically and ecologically important green algal species with a large potential in seaweed aquaculture due to its high productivity, wide environmental tolerance, as well as interesting functional and nutritional properties. Here, we performed a series of manipulative cultivation experiments in order to investigate the effects of irradiance (50, 100, and 160 μmol photons m−2 s−1), temperature (13 and 18 °C), nitrate (< 5, 150, and 500 μM), phosphate (< 1 and 50 μM), and pCO2 (200, 400, and 2500 ppm) on the relative growth rate and biochemical composition (fatty acid, protein, phenolic, ash, and biochar content) in indoor tank cultivation of Swedish U. fenestrata. High irradiance and low temperature were optimal for the growth of this northern hemisphere U. fenestrata strain, but addition of nutrients or changes in pCO2 levels were not necessary to increase growth. Low irradiance resulted in the highest fatty acid, protein, and phenolic content, while low temperature had a negative effect on the fatty acid content but a positive effect on the protein content. Addition of nutrients (especially nitrate) increased the fatty acid, protein, and phenolic content. High nitrate levels decreased the total ash content of the seaweeds. The char content of the seaweeds did not change in response to any of the manipulated factors, and the only significant effect of changes in pCO2 was a negative relationship with phenolic content. We conclude that the optimal cultivation conditions for Swedish U. fenestrata are dependent on the desired biomass traits (biomass yield or biochemical composition).

Effects of geographical location on potentially valuable components in Ulva intestinalis sampled along the Swedish coast

“…Conversely, Gao, Clare, Chatzidimitriou, Rose, and Caldwell (2018) found that lipid (and protein) content increased at elevated nutrient levels. In line with these findings, U. fenestrata produced in defined tank cultivation increased the fatty acid and protein contents at high nitrate concentration and at low illumination (Toth et al, 2020). Reports also show positive effects of increased temperature (20-25°C) on lipid and protein contents, as well as lowered ash content for Ulva spp.…”

Algal proteins: Production strategies and nutritional and functional properties

“…For cultured or bioreactor-grown algae, changing the medium composition is a straightforward way to improve protein content. For instance, the increase of nitrogen, phosphate, and CO 2 seems enhance protein accumulation in algae (Kumari et al, 2014;Tossavainen et al, 2019;Toth et al, 2020). As an example, Tossavainen et al (2019) concluded that, in high-nitrate medium (0.5 g/L of ammonium sulfate), protein content of Euglena gracilis varied between 17.51 and 18.56% of dry weight, while under lower concentrations or absence of nitrogen (0.2 g and 0.0 g/L of ammonium sulfate, respectively), algal proteins in biomass ranged between 10.99 and 12.09% of dry weight.…”

“…Given the worldwide guidelines pointing towards more sustainable and "greener" processes based on circular economy and zero-waste concepts, it is possible, for instance, to improve biomass and metabolites' productivity while treating industrial wastewater streams or taking advantage of the great organic load of agro-industrial by-products to supress the nutritional needs of algae (Kazir et al, 2019). In the particular case of algal proteins, it is known that the growth using nitrogen-or phosphorus-rich substrates might trigger their overproduction, enabling the potential application of the aforementioned underrated streams as means of increasing algae's protein content (Kumari et al, 2014;Tossavainen et al, 2019;Toth et al, 2020).…”

“…Several strategies might play an important role on leveraging a broader commercialization of algal products. From a technical point of view, the development of innovative PBR designs envisaging the optimization of mass transfer properties and the retention of CO 2 in algal cultures, might improve its uptake leading to higher protein content, since CO 2 -rich environments seem to favour protein production by algae (Toth et al, 2020). However, attention must be paid to the prevalence of CO 2 in the medium for large periods of time once it can be responsible for unwanted acidification of the culture and jeopardize the whole growth process.…”

Environmental Impact on Seaweed Phenolic Production and Activity: An Important Step for Compound Exploitation

“…However, for the full exploitation of this technique, there is a need to develop cultivation methods from a multidisciplinary perspective. Preliminary cultivation studies can allow the control and understanding of the impact of extrinsic and intrinsic factors, in order to obtain a specific yield and quality of a certain seaweed compound, with a high rate of success, without putting pressure in the wild seaweed community while also reducing production costs [ 1 , 97 , 115 , 127 , 128 , 129 , 130 , 131 , 132 , 133 , 134 , 135 , 136 , 137 , 138 , 139 , 140 , 141 , 142 , 143 , 144 , 145 ].…”