Regulation of biological activity of surfactants under cultivation of Acinetobacter calcoaceticus IMB B-7241 on glycerol

Abstract

Introduction. The aim of this research was to study the biological activity of surfactants synthesized by Acinetobacter calcoaceticus IMV B-7241 in the medium with glycerol of various degrees of purification and high content of calcium cations (activators of NADH+-dependent glutamate dehydrogenase, which is a key enzyme of biosynthesis of surface-active aminolipids responsible for antimicrobial activity of surfactant complex). Materials and methods. Cultivation of A. calcoaceticus was carried out in liquid mineral medium using as substrates refined glycerol and the waste from biodiesel production. The base medium did not contain calcium chloride, the content of CaCl2 in the modified medium was 0.1 and 0.2 g/l. Surfactants were extracted from the supernatant of the culture luquid with a modified mixture of Folch. The number of adhered cells and the degree of biofilm destruction in the presence of surfactants was determined by spectrophotometric method, antimicrobial activity of surfactants - by the minimum inhibitory concentration (MIC). Results and discussion. It was found that the additional introduction of 0.1−0.2 g/l of CaCl2 into cultivation medium with refined glycerol was accompanied by the synthesis of surfactants, the MIC of which against bacteria (Bacillus subtilis BТ-2, Enterobacter cloacae C-8, Staphylococcus aureus BМS-1) and yeast (Candida albicans D-6) were 1.01–21.3 μg/ml and were 1.4–29 times lower compared to the MIC of surfactants obtained in base medium (1.83−58.8 μg/ml). The adhesion of test cultures on abiotic materials treated with such surfactants was 8–13% lower, and the degree of biofilms destruction was 5–19% higher compared to the values, established for surfactants obtained on base medium. The increasіng antimicrobial and anti-adhesive activity of surfactants synthesized on waste of biodiesel production was observed only when CaCl2 was introduced into the medium at a concentration of 0.2 g/l. Surfactants synthesized in the presence of calcium cations in the medium with the waste of biodiesel production proved to be more effective destructors of bacterial biofilms in comparison with those obtained in the base medium only at low concentrations (0.7–5.5 μg/ml). Conclusion. The results demonstrate the possibility of regulating the biological activity of A. calcoaceticus IMV B-7241 surfactants by changing in the composition of medium content of calcium cations - activators of NADH+-dependent glutamate dehydrogenase (key enzyme of surface-active aminolipids biosynthesis). Surfactants synthesized under different cultivation conditions of A. calcoaceticus IMB B-7241 on glycerol are more effective biofilm destructors and antimicrobial and anti-adhesive agents compared to the known lipopeptides and rhamnolipids formed on glycerol.