Nitrate and phosphate uptake dynamics in two halotolerant strains of Chlorella vulgaris is differentially influenced by carbon, nitrogen and phosphorus supply

Microalgae are attractive for the development of environmentally sustainable processes with the option for carbon fixation, given the photosynthetic capacity of these microorganisms. Nitrogen and phosphorus are key nutrients for microalgal growth as well as carbon fixation and product formations. These are also important nutrients in agriculture, the sustainable supply of which is a challenge. They are often lost in waste streams but can be effectively recovered using microalgae and made available for agriculture. In this investigation, we systematically examined the nitrate and phosphate uptake response of two halotolerant strains of Chlorella vulgaris exposed to four carbon and three nitrogen and phosphorus supply regimes to develop an understanding of the relationship between uptake and supply in two microalgae strains from a similar habitat. Markedly differential response to changes in carbon and nutrient supply regimes were noted between the supply regimes and the strains. Changes in carbon supply was found to significantly influence nitrogen and phosphorus uptake in the two strains. Kinetics of nutrient depletion and carbon fixation were observed to be dynamic and non-linear for both the strains, under high carbon and nutrient supply regimes. This investigation provides for the first time a clear evidence base for the role of supply regimes in the management of nutrient uptake in microalgae, including the relationship between the two, and the significance of carbon supply in nitrogen and phosphorus uptake by microalgae. This will enable development of sustainable processes and predictable strategies involving microalgae towards net-zero solutions, as well as nitrogen and phosphorus recovery from waste streams.