Cerium dioxide nanoparticles (CeO2 NP) have significant catalytic and antioxidant properties due to their ability to inhibit the development of free-radical reactions due to a combination of superoxidedismutase and catalase mimetic activities. This nanopreparation has a significant antibacterial effect, but is low-toxic to unicellular yeast Saccharomyces cerevisiae. Therefore, it is relevant and appropriate to study the effect of this compound on other groups of yeast, in particular members of the genus Rhodotorula spp., which are characterized by high growth rate, unpretentiousness to the component composition of the culture medium, the ability to form a variety of valuable biologically active compounds, as well as the ability to synthesize proteins, lipids, carotenoids and exopolysaccharides in the complex. The report that microorganisms of this genus have been identified as part of the normal fish microbiota (Abramis brama, Rutilus rutilus, Perca fluviatilis, Oreochromis niloticus) expands the range of their use, either as probiotics in general or their individual cellular and extracellular components as prebiotics. In this work, the effect of different concentrations of CeO2 NP nanopreparation on the production parameters of Rhodotorula glutinis was studied, as well as their antagonistic properties after saturation of nanocerium were tested. To detect the optimal concentration of nanopreparation of cerium dioxide, R. glutinis was cultured for 120 h at 28 0C and aerated at 160 rpm on Saburo medium with the addition of citrate-stabilized CeO2 NP with a particle size of 1-2 nm in the following concentrations: 100 mM, 10 mM, 1 mM, 0,1 mM, 0,01 mM. The control was R. glutinis grown on Saburo medium, experimental controls were represented by microorganisms in the culture medium of which citrate and full-size cerium (CeCl3) were added. It was found that most of the studied concentrations of CeO2 NP (except for the highest) are not toxic to these carotenogenic yeasts. The presence of 10 mM CeO2 NP stimulates the growth of the culture, while the increase in biomass is increased by fourfold compared to the control. There was also an increase in the content of basic metabolites – protein by 1,2 times, lipids by 2,5 times and valuable biologically active compounds - carotenoids by 20% and exopolysaccharides by 2,2 times. However, under these conditions, no significant changes in catalase and superoxidase activities were registered. Examination of the antagonistic properties of the CeO2 NP-enriched culture of R. glutinis by delayed antagonism by the method of perpendicular strokes against gram-positive B. subtilis and gram-negative P. syringae bacteria showed the presence of lysis zones up to 17 and 25 mm, respectively, in contrast to their complete or complete absence (2 mm), noted in the study of control samples. A study of the resistance of CeO2 NP-enriched culture of R. glutinis to natural inhibitors of the digestive tract showed resistance of microorganisms to gastric juice (the amount of CFU is 1,4 times higher than control values) and bile (recorded a 5-fold increase in survival of microorganisms). The obtained results testify to the prospects of using nanocerium for mobilization of growth, enzymatic, antagonistic activities of R. glutinis culture.
Optimization of pineapple pulp residue hydrolysis for lipid production by Rhodotorula glutinis TISTR5159 using as biodiesel feedstock
