Master of Science (MSc)
Faculty of Science
Dr. Allison McDonald
Biological pigments, also called biochromes, are coloured compounds which are displayed by a variety of life forms, including animals, due to selective colour absorption. The combination of light absorption and reflection enables each pigment to portray a distinct colour which results in the broad spectrum of colours we observe in our surroundings. Carotenoids are a large group of yellow, orange, and red biological pigments found in living organisms. Our current biomolecular knowledge of carotenoids is heavily derived from studying the pathway in photosynthetic prokaryotes, bacteria, fungi, and plants. Carotenoid pigments are exceptionally multifunctional as they act as photo-protectors against UV damage, antioxidants, colour attractants, precursors for both plant and non-photosynthetic hormones, precursors of retinol (derived from vitamin A, essential for the eye) and are known to be very efficient physical and chemical quenchers of singlet oxygen, as well as potent scavengers of other reactive oxygen species (ROS). Although the biosynthetic pathway is well explored in plants, bacteria, and fungi and there is an understanding of the function of carotenoids in these organisms, there is a substantial knowledge gap in the animal carotenoid biosynthesis pathway that needs to be addressed in order to fully understand how carotenoids are produced. Scientists believe that animals do not have the endogenous enzymes required, such as those in plants, bacteria, and fungi, to biosynthesize carotenoids. Instead, it is widely believed that animals acquire carotenoids through their diet to produce these pigments, in a process termed carotenoid bioconversion. A carotenoid of prime focus for its antioxidative and photoprotective properties is the red, keto-carotenoid, astaxanthin. The marine copepod Tigriopus californicus exhibits a bright orange-red colouration that is predominantly composed of astaxanthin. For this thesis, carotenoid biosynthesis in T. californicus was investigated using bioinformatics to test the hypothesis that animals cannot biosynthesize carotenoids de novo. Initially the egg sacs of gravid female T. californicus were examined to comprehend the characteristics of the egg sac, the maternal carotenoid deposition to developing embryos, and to study the use of carotenoids by the nauplii life stages. With the addition of these observations, the potential influence of diet on the colour of T. californicus adults was also tested by using a carotenoid free diet of nutritional yeast. After successfully decreasing the carotenoid pigmentation displayed by the copepods on the nutritional yeast diet, new copepod generations were observed. This demonstrated that under in vitro laboratory conditions, T. californicus does not require astaxanthin (or other carotenoid pigmentation) in order to fully complete all stages of its life cycle. However, on the carotenoid free nutritional yeast diet the copepods were still able to produce trace amounts of colouration throughout the body and a deep orange/red colouration was observed in the eyespot region. Since it is known that carotenoids are used as precursors for vitamin A, and subsequently a prerequisite for the production and activation of retinal and rhodopsin required by the eyespot, it was putatively determined that T. californicus are using “building block” precursors from the yeast diet and encode genes for carotenoid biosynthesis. In support of this hypothesis, using bioinformatic analysis, essential putative carotenoid enzymes were identified in T. californicus, and other animals. The findings from this original research provide evidence that supports the theory that animals have the potential to biosynthesize carotenoids without the assistance of diets that consists of pre-existing carotenoid precursors.
Balasubramaniam, Anchalya, "A Bioinformatic Analysis of the Biosynthesis of Carotenoids in the Copepod Tigriopus californicus" (2021). Theses and Dissertations (Comprehensive). 2400.