Proteolytic Activity of Bacillus Strains Isolated from Soil of Rice Agrocenosis

Abstract

Microorganisms are the most common sources of commercial enzymes due to their physiological and biochemical properties, facile culture conditions, and ease of cell manipulation. Among microbial enzymes, proteases are ubiquitous in nature and have been found in all living forms encompassing the eukaryotes like plants, animals, fungi, and protists as well as the prokaryotic domains of bacteria and archaea. Proteases are the most important for the industry and constitute approximately 60% of the total industrial enzyme market. Among the bacteria, the genus Bacillus has a very prominent place in terms of the commercial production of proteases. Earlier from the water and bottom sediments of the Black Sea, we have isolated a number of producers of proteolytic enzymes from Bacillus species. The aim of this work was to investigate the ability of representatives of a number of soil bacilli species to synthesize enzymes that hydrolyze such protein substrates as elastin, fibrin, fibrinogen, and keratin. Methods. The objects of the study were 8 cultures (KS 1 — KS 8) isolated from the soil of the rice agrocenosis. Cultures were grown under conditions of deep cultivation at 28 °С, with a mixing speed of for the nutrient medium of 230 rpm for 4 days. Methods of determining proteolytic (caseinolytic, elastolytic, fibrinolytic, fibrinogenolytic, and keratinase) activity in the culture liquid supernatant were used. Disulfide reductase activity was measured spectrophotometrically at 412 nm by evaluating the yellow sulfide formed during the reduction of 5,5’-dithiobis-(2-nitrobenzoic acid) (DTNB). Results. The study of the spectrum of proteolytic activities of 8 freshly isolated strains showed that only KS 6 under experimental conditions did not show the ability to hydrolyze any of the studied substrates (casein, elastin, fibrin, fibrinogen, and keratin). Strains KS 1, KS 2, KS 7, and KS 8 showed higher levels of activity compared to other strains studied. The most interesting for further research are: І) strain KS 1, which showed the highest fibrinolytic activity, ІІ) strain KS 2 as the most effective producer with elastase and fibrinogenolytic activity, III) KS 7 and KS 8, which simultaneously showed the highest rates as keratinase (7 U/mL and 9 U/mL) and sulfate reductase (33 μmol/min and 31 μmol/min) activity, respectively. Conclusions. According to the catalytic properties, a number of representatives of Bacillus, isolated from the soil of the rice agrocenosis may be promising for further research as an enzyme producer with proteolytic activity.