Nitrile-Hydrolyzing Haloalkalitolerant Rhodococci of Soda Sludge Storage

The goal of the work is to study the growth characteristics, nitrile-hydrolyzing activity and biofilm formation of Rhodococcus qingshengii IEGM 1416 and R. erythropolis IEGM 1417 under the effect of harsh environmental conditions (high mineralization, high pH, and solvents). The haloalkalitolerant nitrile-utilizing R. qingshengii IEGM 1416 and R. erythropolis IEGM 1417 were isolated from an alkaline highly mineralized soda sludge storage, and their ability to accumulate biomass at high salt concentrations and high pH was studied. The effect of pH 10 and 50 g/L NaCl on nitrile-hydrolyzing activity, as well as the ability to grow in the presence of high concentrations of nitriles and other solvents, were studied. R. qingshengii IEGM 1416 was isolated from soda sludge with pH 11. This strain accumulates 2 times more biomass at pH 10 than at pH 8, and its nitrile-hydrolyzing activity is 2.5 times higher at pH 10 than at pH 7 of the reaction medium. Extremely high tolerance of these strains to nitriles was established. R. qingshengii IEGM 1416 and R. erythropolis IEGM 1417 are able to grow at 1.5 M acetonitrile and acrylonitrile, and at 10-80% hexane. Biofilm formation is an adaptive ability of these strains. NaCl (50-200 g/L) in cultivation media and pH 10-12 course to an increase in the R. qingshengii IEGM 1416 biofilm biomass relative to the control (0.5 g/L NaCl, pH 7). Biofilm biomass of R. erythropolis IEGM 1417 increases under 10-200 g/L NaCl and pH 8-12. The biofilm biomass of both strains significantly decreases at 37 °C compared to 30 °C. It has been shown that the extreme habitat of nitrile hydrolyzing bacteria affects their ability to hydrolyze nitriles in a highly mineralized and alkaline environment. Nitrile-hydrolyzing haloalkalitolerant rhodococci are a promising biotechnological object and can be used in the nitrile hydrolysis under high pH and mineralization.