Characterization of Rhodotorula rubra TP1 mutants

Mallidi, Subhashini (2003) Characterization of Rhodotorula rubra TP1 mutants. Masters thesis, Memorial University of Newfoundland.

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Abstract

Carotenoid pigments exist in nature and are widely distributed as colourants throughout the biological systems, such as microalgae, insects, birds, fish and crustaceans. They are responsible for interesting colours seen in various parts of these organisms, which play a great role in the biological functions like photoreception and photosynthesis. Carotenoids are mainly used as pigments for colouration of food products and pharmaceuticals. They also function as antioxidants and help in minimizing membrane-damage, and in controlling human diseases such as cancer, cataract and atherosclerosis. -- Astaxanthin is a red orange carotenoid produced by aquatic organisms such as algae and is also found in yeasts like Phaffia rhodozyma and Rhodotorula rubra. It is used as a pigment in feed for salmon and shellfish and also enhances immune response of fish and shrimp. Among yeasts, R. rubra TP1 is a good source of red pigment and whole cells induce pigmentation in fish. It has been shown in earlier work that R.rubra has faster growth rate, shorter incubation-time and yields more biomass than P.rhodozyma. Further, previous feeding-trial experiments carried out using rainbow trout have been successful and therefore R. rubra TP1 has economic potential. -- In the current work the mutants M1, M2 and M3 of R. rubra TP1 were characterized and their properties compared with those of the wild type yeasts. The optimal pigment production was determined by growing the mutants and wild type yeasts under different growth conditions, such as different substrates, temperatures, initial pH and light. The maximum pigment recovery was achieved by using different extraction methods which include French Press method, Freeze- dried cells, sonication and enzymatic cell breakage. The spectrophotometer graph and Thin Layer Chromatograpy (TLC) techniques were used to estimate the total carotenoid concentration and to analyse the pigment in each sample. -- The experimental results showed that light enhances pigment production. Yeast malt broth with peat extract as a nitrogenous source showed more biomass yield. Bacto czapex dox broth was found to be inhibitory to growth of the mutants of R. rubra TP1. The cells gave more pigment at 25 °C in the initial pH range of 5.0 to 7.0. The French press method was found to be more efficient to extract the optimum pigment for M1, M2 and M3 with values 250.6, 254.4 and 193.2 μg/g, respectively. Mutant 2 alone gave higher recovery of the pigment with Freeze- dried method. Sonication method gave less pigment recovery. The enzymatic method with a pH of 7.0 for all mutants gave recovery values of 184.4, 164.2 and 129.4 μg/g for M1, M2 and M3, respectively. The pigment analysis confirmed that all the mutants contain β-carotene, torulene and torularhodin carotenoids in their pigments.

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