Microalgal species prospecting and characterisation for salinity tolerance, nutrient remediation and bio-product potential

von Alvensleben, Nicolas (2015) Microalgal species prospecting and characterisation for salinity tolerance, nutrient remediation and bio-product potential. PhD thesis, James Cook University.

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Microalgae provide a multidisciplinary approach for waste-gas and –water remediation offering parallel production of bio-products including nutraceuticals, food, feed, fertiliser and fuel. The main challenges for microalgal biomass production in Australia are limited freshwater resources (most of which are slightly saline), high light intensities and high temperatures, the latter in particular in the dry tropics.

In line with the AMCRC-funded microalgae carbon dioxide emission abatement and bio-product development project at Australian coal-fired power plants to which this research was linked, establishing salinity tolerance of endemic microalgal species was a priority due to the varying salinities of available tailings-dam waters for cultivation at the different sites (freshwater to marine). Through complete biochemical profiling (total lipids, protein, carbohydrate and fatty acids and fatty acid profiles), this thesis provided much needed baseline information on the potential of endemic microalgae cultivation for bio-product potential of a carbon dioxide emissions abatement strategy. As tailing dam waters are nutrient-poor, fertilisation requirement was also investigated, which simultaneously also provided inferences for species selection with remediation potential of nutrient-rich waste-waters. The potential use of salinity for cyanobacterial contamination control in halotolerant microalgal species was also investigated. Microlagal carotenoid contents and profiles were investigated for high-value nutraceutical production potential. For this, nine microalgal species were screened for carotenoid responses under moderate high light, in nutrient-replete and -deplete conditions and with added molybdenum and vanadium in concentrations found in Stanwell Corp. tailings-dam water.

Salinity tolerance (2 to 36 ppt) under nutrient-replete and –deplete conditions was established for Picochlorum atomus, Desmodesmus armatus, Mesotaenium sp., Scenedesmus quadricauda and Tetraedron sp. using growth rates. Picochlorum atomus was selected for its demonstrated growth performance under outdoor tropical conditions, while Desmodesmus armatus, Mesotaenium sp., Scenedesmus quadricauda and Tetraedron sp. were isolated from Stanwell Corp. tailings-dam water and were selected for their ability to tolerate the polluted waters at this site.

The euryhaline Picochlorum atomus was identified as suitable for nutrient remediation, as was Scenedesmus quadricauda up to 11 ppt. Lipid contents and fatty acid profiles of both species were suitable for biofuel production. Mesotaenium sp. (up to 8 ppt) was suitable for cultivation in oligotrophic tailings-dam waters at coal-fired power stations, leading to substantial potential savings on fertilisation costs for biofuel and bioethanol production. Desmodesmus armatus showed intermediate salinity tolerance and nutrient uptake and would be a suitable species for food and feed production due to high protein contents. These findings provide a basis for species selection based on site-specific salinity conditions and nutrient resource availability. Additional findings also indicate that high salinity (28-36 ppt) can be used to inhibit contamination by the freshwater cyanobacteria Pseudanabaena limnetica, a common problem in the tropics.

Transition metals have been shown to induce radical oxygen species production in microalgae, often resulting in the production of antioxidants and radical scavenging compounds such as carotenoids, which can be exploited for the production of nutraceuticals and bioactive pharmaceuticals. Tailings-dam water at the Stanwell Corp. coal-fired power station contains significant amounts of these trace metals. Therefore, to enable pigment-product based species selection, a pilot-study (chapter 4) explored the effects of molybdenum and vanadium on carotenoid production in eight microalgal species (Desmodesmus armatus, Desmodesmus maximus, Coelastrum proboscideum, Graessiella emersonii, Haematococcus sp., Scenedesmus quadricauda, Mesotaenium sp., Tetraedron sp.), in nutrient-sufficient and -deplete conditions under increased irradiance (~400 μmol photons m⁻² s⁻¹). The majority of species were isolated from Stanwell Corp. coal-fired power station and were chosen for their ability to grow in polluted tailings-dam waters, except C. proboscideum and G. emersonii which were isolated in North East tropical Queensland and were selected for their astaxanthin production potential. Haematococcus sp., which was obtained from CSIRO, was included as a positive control for astaxanthin production. Both vanadium and molybdenum induced small increases of astaxanthin, lutein, violaxanthin and β-carotene content in most species, in particular Haematococcus sp., which together with D. armatus also showed the highest pigment concentrations. Coelastrum proboscideum and G. emersonii both produced astaxanthin, making them interesting alternatives to Haematococcus sp. for commercial astaxanthin production. These species were selected for chapter 5 to investigate the interactive effects of molybdenum and high temperature under moderately high irradiance in a factorial design, which are likely on-site cultivation conditions during the Australasian summer.

Overall, the main driver of pigment concentration changes was high light in particular in D. maximus, whereas high temperature was the main stressor in Haematococcus sp. Graesiella emersonii produced the highest concentrations of important xanthophyll cycle pigments (violaxanthin and zeaxanthin), with no effects of Mo making this species suitable for cultivation in tailings-dam waters. In contrast, high concentations of violaxanthin in Desmodesmus armatus could only be sustained without Mo, suggesting production in high-nutrient waters void of metal pollution should be considered. Haematococcus sp. had the highest concentrations of astaxanthin in response to high temperature stress which was enhanced slightly in the presence of Mo, making it suitable for tailings-dam water cultivation, but requiring a 2- step cultivation process for (i) biomass and (ii) astaxanthin production. This study identified Coelastrum proboscideum as an alternative astaxanthin producer. Although astaxanthin concentrations were lower, growth data suggest that a single-step cultivation approach could be feasible. Additionally, this study identified Desmodesmus maximus, Desmodesmus sp. and G. emersonii as potential species for commercial lutein production as an alternative to Marigold (Tagetes sp.) flowers due to higher lutein concentrations, offering the added advantage of independence of arable land and coupling production to remediation of tailings-dam water for Desmodesmus sp. and G. emersonii. In contrast, Mo treatment significantly lowered lutein concentrations in D. maximus making it a suitable species for coupled nutrientrich water remediation and lutein production.

In summary, this thesis characterised endemic microalgal species for cultivation at industrial sites of varying salinity and nutrient availability, with further identification of low- to high-value bio-product potential.

Item ID: 46020
Item Type: Thesis (PhD)
Keywords: amino acids; bio-plastic; bio-products; biotechnology; carotenoids; chlorophyta; fatty acid profiles; microalgae; nutraceutical products remediation; salinity
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 2: von Alvensleben, Nicolas, Stookey, Katherine, Magnusson, Marie, and Heimann, Kirsten (2013) Salinity tolerance of Picochlorum atomus and the use of salinity for contamination control by the freshwater cyanobacterium Pseudanabaena limnetica. PLoS ONE, 8 (5). pp. 1-12.

Chapter 3: von Alvensleben, Nicolas, Magnusson, Marie, and Heimann, Kirsten (2016) Salinity tolerance of four freshwater microalgal species and the effects of salinity and nutrient limitation on biochemical profiles. Journal of Applied Phycology, 28 (2). pp. 861-876.

Date Deposited: 11 Oct 2016 02:14
FoR Codes: 07 AGRICULTURAL AND VETERINARY SCIENCES > 0704 Fisheries Sciences > 070401 Aquaculture @ 33%
10 TECHNOLOGY > 1002 Environmental Biotechnology > 100203 Bioremediation @ 33%
10 TECHNOLOGY > 1003 Industrial Biotechnology > 100302 Bioprocessing, Bioproduction and Bioproducts @ 34%
SEO Codes: 83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8301 Fisheries - Aquaculture > 830199 Fisheries - Aquaculture not elsewhere classified @ 33%
86 MANUFACTURING > 8601 Processed Food Products and Beverages (excl. Dairy Products) > 860105 Nutraceuticals and Functional Foods @ 33%
82 PLANT PRODUCTION AND PLANT PRIMARY PRODUCTS > 8203 Industrial Crops > 820399 Industrial Crops not elsewhere classified @ 34%
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