Carbohydrate components of culture media as determinants of the Rhodosporidium diobovatum IMB Y-5023 yeast metabolism

Abstract

Background. The basidiomycete Rhodosporidium diobovatum is an oleaginous yeast capable of carotenoid synthesis. Scientific research on this yeast indicates that it can be a promising industrial producer of this pigment. The yeast is capable of assimilating numerous carbon substrates and it can grow under various, often extreme, environmental conditions. Wild strains can be isolated from soil, the depths of the sea and the surface of plants. They can grow both in the dark and in the presence of light. The aim of this study was to determine the capability of the Rh. diobovatum IMB Y-5023 yeast strain to produce and accumulate carotenoids when cultured on media with different carbohydrate concentration and composition and with low monosaccharide levels. The yeast was cultured at different illuminances. This research is of great theoretical and practical importance, because it may enable the use of various organic by-products from the agri-food industry as substrates for culturing Rh. diobovatum and for microbial production of carotenoids. This research also provides an opportunity to reduce the costs of the microbiological process by choosing optimal illuminance of the culture. Material and methods. Rhodosporidium diobovatum IMB Y-5023 was cultured on three test media: CM (carrot medium), BYP (wheat bran extract), and the YM medium with higher concentration of malt extract as the main source of oligosaccharides and with maltotriose added. Cultures were carried out at 22°C for 5 days at illuminance ranging from 0 to 5,000 lx. The carbohydrate composition of the media was determined before and after the culturing of Rh. diobovatum IMB Y-5023 by means of UHPLC coupled with tandem mass spectrometry (MS). The following parameters were also measured after culturing: biomass yield (DCW – dry cell weight, g/l), the concentration of carotenoids in the yeast biomass (mg/g DCW), the biomass yield coefficient (YX/S) Ielchishcheva, Iu., Stachowiak, B., Szwengiel, A., Bozhkov, A. (2017). Carbohydrate components of culture media as determinants of the Rhodosporidium diobovatum IMB Y-5023 yeast metabolism. Nauka Przyr. Technol., 11, 3, 291–303. http://dx.doi.org/10.17306/J.NPT.00210 292 and the carotenoid yield coefficient (YC/S). The samples were compared by means of cluster analysis (CA) and principal component analysis (PCA), which were used to visualise the relationships between the study variables and the samples. Results. The Rh. diobovatum IMB Y-5023 yeast strain grew and produced carotenoids on all the media. It assimilated the DP3 and DP4 oligosaccharides contained in the media. Regardless of the illuminance during culturing, the consumption of sugars in the test media remained at 90% or more. However, the concentration and type of carbohydrates in the test medium affected the course of their metabolism. Regardless of the illuminance, the highest concentration of pigments in the cells and the lowest yield of biomass were noted with YM. The initial concentration of sugars in that medium was three–four times greater than in the other test media, and their type was considerably diversified. The data clustering (CA) and principal component analysis (PCA) showed that the BYP and CM media (with similar initial sugar concentrations of 11–15 g/l) had similar influence on the yeast metabolism, whereas the measured variables were completely different in the cultures with the YM medium. Conclusions. The Rh. diobovatum IMB Y-5023 yeast strain is a promising industrial producer of carotenoids. It can effectively assimilate both monosaccharides and DP3 and DP4 oligosaccharides. It does not require illumination to grow and produce pigments effectively, especially when it is grown on media that have high sugar concentrations and are rich in oligosaccharides. The cost of industrial carotenoid production with Rh. diobovatum IMB Y-5023 can be reduced by using inexpensive by-products from the agri-food sector as a culture medium, and by eliminating the illumination of cultures.