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Carotenogenic yeasts are non-conventional oleaginous microorganisms capable of utilizing various waste substrates. In this work, four red yeast strains (Rhodotorula, Cystofilobasidium, and Sporobolomyces sp.) were cultivated in media containing crude, emulsified, and enzymatically hydrolyzed animal waste fat, compared with glucose and glycerol, as single C-sources. Cell morphology (cryo-SEM (cryo-scanning electron microscopy), TEM (transmission electron microscopy)), production of biomass, lipase, biosurfactants, lipids (gas chromatography/flame ionization detection, GC/FID) carotenoids, ubiquinone, and ergosterol (high performance liquid chromatography, HPLC/PDA) in yeast cells was studied depending on the medium composition, the C source, and the carbon/nitrogen (C/N) ratio. All studied strains are able to utilize solid and processed fat. Biomass production at C/N = 13 was higher on emulsified/hydrolyzed fat than on glucose/glycerol. The production of lipids and lipidic metabolites was enhanced for several times on fat; the highest yields of carotenoids (24.8 mg/L) and lipids (54.5%/CDW (cell dry weight)) were found in S. pararoseus. Simultaneous induction of lipase and biosurfactants was observed on crude fat substrate. An increased C/N ratio (13–100) led to higher biomass production in fat media. The production of total lipids increased in all strains to C/N = 50. Oppositely, the production of carotenoids, ubiquinone, and ergosterol dramatically decreased with increased C/N in all strains. Compounds accumulated in stressed red yeasts have a great application potential and can be produced efficiently during the valorization of animal waste fat under the biorefinery concept.

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Raman spectroscopy has a broad range of applications across numerous scientific fields, including microbiology. Our work here monitors the influence of culture media on the Raman spectra of clinically important microorganisms (Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis and Candida albicans). Choosing an adequate medium may enhance the reproducibility of the method as well as simplifying the data processing and the evaluation. We tested four different media per organism depending on the nutritional requirements and clinical usage directly on a Petri dish. Some of the media have a significant influence on the microbial fingerprint (Roosvelt-Park Institute Medium, CHROMagar) and should not be used for the acquisition of Raman spectra. It was found that the most suitable medium for microbiological experiments regarding these organisms was Mueller-Hinton agar.

Red yeast strains are ubiquitous microorganisms which accumulate substantial amounts of lipids and lipid-soluble metabolites. Red yeasts utilize many waste substrates of different origin. In this work red yeasts strains (Rhodotorula, Sporobolomyces, Cystofilobasidium) were used for screening of growth and metabolic activity. As a carbon source waste animal fat and its hydrolysis products were used. Hydrolysis of animal fat was tested in alkaline as well as acidic conditions. As the substrate glucose (control), glycerol, crude animal fat, acid fat hydrolyzate and hydrolysate: glucose 1:2 were used. Screening of growth and metabolic activity of red yeasts was performed by flow cytometry. Extracellular lipase production was monitored as adaptation mechanism. Carotenoids, ergosterol and ubiquinone were quantified by HPLC/PDA/MS/ESI and the biomass was evaluated gravimetrically. All tested strains utilized fat hydrolysate and produced red coloured biomass. Cultivation in media containing non-hydrolysed fat led to strain specific induction of extracellular lipase. Amount of lipid metabolites produced by individual strains was depended on glycerol content in medium. The highest increase of lipase production was observed in Cystofilobasidium macerans and Sporobolomyces shibatanus. Valorisation of animal fat can lead to production of unsaturated fatty acids, single cell oils, carotenoid pigments, sterols and enriched red yeast biomass.