The yeast strain Yarrowia lipolytica IPS 21 was tested for its ability to degrade potentially toxic chrome-tanned leather shavings (CTLS) in a liquid environment. Biological and chemical parameters were monitored during a 48-h period of biotransformation of the protein-rich waste. CTLS was added at a concentration of 0.1-4% (wt/wt) to a modified YPG medium (15 g L-1 yeast extract and 5 g L-1 NaCl). Biodegradation and bioconversion were performed in a one-step process. It was found that the higher degradation rate depended on the activity of the proteases and the pH of the medium, but not on the initial inoculum ratio and the activity of the dehydrogenase. The highest efficiency of the process was obtained for 4% (wt/wt) CTLS on day 2 (degradation rate 58-67%, biomass production 2.11-2.20 g L-1, protease activity 312 U mg-1 protein, and pH 9.20). Our results showed that total chromium was probably not transported across the cytoplasmic membrane of Y. lipolytica IPS21 and that chromium (III) was not oxidized to chromium (VI). The phytotoxicity of selected amino acid supernatants [2.5% (vol/vol)] was tested after the bioconversion process. It was found that the supernatants had a stimulating effect on the plants tested. The root elongation was 29-28% higher than that of the reference samples. This result makes Y. lipolytica IPS21 a potential candidate for safely converting potentially toxic protein-rich wastes into valuable products without enzyme isolation, e.g., amino acid fertilizers. IMPORTANCE Enzyme technologies have the greatest practical relevance to environmental trends. Overcoming the barrier of the high cost of carbon substrates used for biotransformation is the main challenge of these methods. The huge potential of the use of extracellular proteases of Yarrowia species or amino acids in various industries indicates the need for the extension of basic research on waste as a carbon source for this yeast. The experiments demonstrated that it is possible to use Y. lipolytica IPS21 for bioconversion of chrome-tanned leather shavings (CTLS) in a single-step process and to produce high-value amino acid supernatant without having an isolated enzyme. In our study, we show the effect of 2.5% (vol/vol) CTLS supernatant obtained from Y. lipolytica IPS21 on the elongation of the root system of selected plants and provide information on the effect of environmental factors on the efficiency of the bioconversion and the migration of chromium.
Keywords: Yarrowia lipolytica; amino acids; bioconversion; biodegradation; fertilizers; rich-protein waste; the activity of enzymes.