Biodegradable and non-toxic microbial surfactants have potential application in different industry areas and environment protection due to emulsifying properties, antimicrobial and antiadhesive activity.
However, currently the industrial production of surfactants of microbial origin is limited to a small number of manufacturers, although the production of synthetic surfactants in the world exceeds 20 million tons / year. This situation is due to low efficiency of microbial technologies to produce surfactants, one of the reasons for which is the high cost of the biosynthesis process, as well as the low concentration of synthesized surfactants. One of the approaches to reducing the cost of microbial surfactants is the use of industrial waste as substrates [8-10].
Another problem of technologies for obtaining microbial surfactants is the possibility of changing their properties depending on the conditions of cultivation of the producer; because they are secondary metabolites and are synthesized as a complex of such compounds. Presence of toxic impurities in industrial waste can also affect the chemical composition and, consequently, the properties of the synthesized surfactants.
The dissertation is devoted to the establishment of conditions for cultivation of Rhodococcus erythropolis IMV Ac-5017 on various carbon substrates. These substrates provide the synthesis of surfactants with high antimicrobial and antiadhesive activity (including the ability to destroy biofilms), as well as high efficiency of oil waste destruction.
The dissertation establishes the possibility of replacing traditional substrates with sunflower oil and biodiesel production waste. This allows to dispose of toxic industrial waste and reduce the cost of biosynthesis of surfactants R. erythropolis IMV Ac-5017, as well as to obtain the target product with high biological activity.
It was found that surfactants synthesized by R. erythropolis IMV Ac-5017 on all substrates (ethanol, purified glycerol, biodiesel waste, refined and spent sunflower oil of various qualities) demonstrated high antimicrobial activity against bacteria and yeasts of the genus Candida (minimal inhibiting concentrations 2 - 500 μg / ml). Also they shown the ability (at concentrations 3-9 μg/ml) to reduce the adhesion of test cultures on abiotic surfaces by 25-60%, as well as to destroy bacterial biofilms by 20-80% (at concentrations of 12-30 μg/ml).
Calcium cations were found to be the activators of NADP + -dependent glutamate dehydrogenase (key enzyme of biosynthesis of surface-active aminolipids in R. erythropolis IMV Ac-5017). Additional introduction of CaCl2 (0.1 g/l) into the culture medium of the IMV strain Ac-5017 was accompanied by two fold increase in NADP+ -dependent glutamate dehydrogenase activity and the synthesis of surfactants with the following characteristics:
• minimum inhibitory concentrations 1.2-5 times lower as compared to the test cultures
• adhesion to abiotic materials treated with such surfactants is 12-50% lower,
• the degree of destruction of biofilms is on average 9-10% higher compared to those established for surfactants obtained on a basic medium without Ca2+ .
The addition of 0.1 mM Cu2+ (activator of alkane hydroxylase - the first enzyme of catabolism of n-alkanes) during the exponential phase of growth of R. erythropolis IMV Ac-5017 on non-hydrocarbon substrates (ethanol, hexadecane, spent sunflower oil) was accompanied by the formation of surfactants. These surfactants increased oil degradation by 8-13% as compared to the use of surfactants synthesized in a medium without copper cations.
The degree of destruction of complex oil pollution reached 70-99% after 17-20 days. The complexes contained heavy metals (0.1M Cu2+, 0.01M Cd2+ and 0.01mM Pb2+) and their concentration was 2.6 g/l in water and 20.0 g/kg in soil. The measurement was taken in the presence of 5% culture fluid after growing R. erythropolis IMV Ac-5017 on ethanol, hexadecane and waste oil with the addition of 0.1M Cu2+.
Unlike the world-famous surfactants synthesized by actinobacteria of the genus Rhodococcus, surfactants of the IMV strain AC-5017 are multifunctional. In addition to high efficiency of destruction of oil pollution (including those with heavy metals), these surfactants are characterized by high antimicrobial and antimicrobial activity (e.g ability to destroy biofilms).
Key words: Rhodococcus erythropolis IMV Ac-5017, surfactants, industrial waste, biological activity, destruction of xenobiotics.
