Enhanced β-Carotene Production in Mycolicibacterium neoaurum Ac-501/22 by Combining Mutagenesis, Strain Selection, and Subsequent Fermentation Optimization

Abstract

A continuing interest of scientists regarding the development of new β-carotene production technologies is due to the high biological activity of this compound and its wide application range. Bacteria are considered among the possible β-carotene producers convenient for industrial use. The purpose of this study was to develop a Mycolicibacterium neoaurum strain with an enhanced ability for β-carotene production and to optimize the fermentation conditions to improve the final yield of the target compound. Using chemical mutagenesis with N-nitroso-N-methylurea along with further strain selection, a M. neoaurum strain Ac-501/22, whose productivity was 2.7-fold higher than that of the parental strain Ac-501, was developed. The effect of nitrogen and carbon sources as well as cultivation conditions on the growth of M. neoaurum Ac-501/22 and β-carotene production were studied to select the optimal fermentation regime. Due to an increase in the temperature of cultivation from 30 to 35 °C, replacement of glucose with glycerin (20.0 g/L) and degreased soybean flour with powdered milk (10.0 g/L), and increase in the urea content from 0.5 to 1.0 g/L, the level of β-carotene production was improved to 183.0 mg/kg that was 35% higher than in the control. Further strain fermentation in a 3 L bioreactor using an optimized medium with the pH level maintained at 7.0–7.2 and 50% pO2 provided the maximum output of the target compound (262.4 mg/kg of dry biomass) that confirmed the prospects of the developed strain as an industrial β-carotene producer.