Evaluation of the competitive performance of an indigenous eicosapentaenoic acid producing microalgal isolate

Master Thesis


Permanent link to this Item
Journal Title
Link to Journal
Journal ISSN
Volume Title

University of Cape Town

Omega-3 fatty acids are known to have positive effects on brain function, as well as cardiovascular disease and inflammatory diseases. They currently sold as fish oil concentrates. The fish oil extraction processes are unsustainable due to the diminishing fish stocks in open waters. In addition to this is the fact that the omega-3 fatty acid content in fish are directly dependent on the fish's diet. If the fish does not have access to nutrients containing omega-3s, the fish will not have assimilated the relevant fatty acids. Currently, microalgae are a topic of interest regarding omega-3 fatty acid production because they are the ultimate de nova source of omega-3 fatty acids. In order to mitigate long-term fish resource depletion, it is imperative that the cultivation of edible fish becomes a priority. However, these aquaculture fish will not contain omega-3 fatty acids if this is not a part of their diet, either naturally or as a feed additive. Due to microalgae's de nova production of omega-3 fatty acids, this would be an ideal alternative to fish oil, as well as a source of omega-3 fatty acids for cultivated fish as a feed input. South Africa is an ideal location for the commercialisation of microalgal technology, due to its biodiversity and climate. There is thus a desire to exploit the biodiversity of South Africa and over 750 microalgal isolates have been collected from across South Africa and are housed at the CSIR Biosciences and the Centre for Bioprocess Engineering (CeBER) at the University of Cape Town. The main objective of this study was to investigate whether a locally selected isolate was a more suitable organism for omega-3 fatty acid production in an open raceway pond than a current species of choice. The objectives of the study were achieved by investigating the biomass, EPA production and response to reactor configuration and process conditions, with a view to assessing the potential to further scale up the bioprocess. A literature review was conducted to identify a list of possible omega-3 producing candidates. The published data were analysed to reduce the overall list of potential organisms to six species. Initial experimental analysis indicated that Phaeodactylum tricornutum was a suitable control species against which to compare the locally selected isolate in terms of biomass and EPA production. Average specific growth rate and overall average EPA productivity were 0.24 d-1 and 10.85 ìg.d- 1 respectively for P. tricornutum. The chosen CSIR species, WCA 23.2, had an average specific growth rate and overall average EPA productivity of 0.20 d-1 and 7.83 ìg.d- 1 respectively. Molecular identification confirmed the identity of Phaeodactylum tricornutum and indicated WCA 23.2 most likely to be an Amphora species. Selected environmental factors, such as pH and different nutrient regimes were chosen to study the effect on growth rate, biomass production and EPA production under laboratory conditions. A study was devised to test the effects of pH control under maintained nutrient conditions. All studies were subjected to a period of nutrient deficiency for the last 4-6 days of the experiment to assess the effect on EPA induction. The pH studies resulted in similar average specific growth rates for both species under pH controlled vs. uncontrolled conditions with WCA 23.2 and P. tricornutum demonstrating growth rates of 0.20-0.22 d-1 and 0.30-0.33 d-1 respectively. Specific EPA productivity was negatively affected for both species in the absence of pH control, where- the pH increased to above pH 9.4. For the pH studies, there was no observed increase in EPA content under nutrient (nitrate and silicon) deficient conditions. Subsequent experiments were performed with the pH controlled at pH 8.3 to ensure optimal biomass and specific EPA production. To evaluate the impact of different nutrient addition regimes at a chosen pH, a study was designed to supply cultures with the same amount of nutrients where (1) the batch culture had all the nutrients supplied at the start and (2) a fed-batch regime where smaller amounts of nutrients were supplied every second day. Average specific growth rates were similar for both species under batch and fed-batch conditions with values ranging from 0.23-0.25 d-1. Specific EPA productivities, however, were higher for both cultures when cultivated under the batch conditions with productivities of 0.412 mg.g-1d and 0.175 mg.g-1d for WCA-23.2 and P. tricornutum respectively. To assess the impact of scale-up, biomass and specific EPA production was assessed in an open raceway pond system (SO L volume) where species were cultivated, in duplicate, under batch conditions at a pH of 8.3, relying on the environmental temperatures and natural sunlight. Biomass productivities for both cultures were significantly lower when compared to the productivities from the laboratory scale studies. Biomass productivity was 2.5 times lower for WCA 23.2 and five-fold lower for P. tricornutum. In terms of specific EPA production, WCA 23.2 suffered a 4.5 fold loss while specific EPA production in P. tricornutum was 20% higher. While the locally selected isolate had a lower specific EPA production rate, it was quicker and easier to harvest. WCA 23.2 auto-flocculated and could be sieved within an hour, while P. tricornutum required an additional settling step to harvest the biomass, resulting in an overall harvesting phase that took two days. The experimental data indicated that EPA productivity was higher in P. tricornutum than WCA 23.2, under the conditions tested. However, the ease of biomass recovery and regulatory advantages associated with using an endemic species mean that a more thorough economic evaluation is required to draw a definitive conclusion.

Includes bibliographical references.