Simultaneous copper bioaccumulation, growth and lipase production of Rhizopus delemar in molasses medium: optimisation of environmental conditions using RSM

Abstract

In this study, the bioaccumulation of Cu(II) ions by R. delemar and their influence on growth of the microorganism were assessed, and the impact of Cu(II) ions on the activity of lipase enzyme degradation of lipids in wastewaters by enzymatic hydrolysis was received for consideration. Optimisation of Cu(II) bioaccumulation process was performed by varying three independent parameters (pH, temperature and Cu(II) concentration) using a central composite design (CCD) under response surface methodology (RSM). For the maximum Cu(II) bioaccumulation and lipase production at a desired level of the biomass concentration level, a total of 20 experimental runs were set and the experimental data fitted to the empirical second-order polynomial models. The adequacies of the predicted models for the Cu(II) bioaccumulation, lipase activity and biomass concentration were confirmed by the coefficients of multiple regression (R²), which were adjusted to be 99.6%, 94.5%, 93.4%, respectively indicating reasonably good models for practical implementation. A maximum Cu(II) bioaccumulation of 36.81 mg/L was obtained at pH 6.0, at 32.6°C, and at 50 mg/L initial Cu(II) concentration. The lipase activity of R. delemar decreased only from 505 U/L in Cu(II)-free fermentation medium to 476 U/L in the presence of Cu(II) giving 5.74% decrease in lipase activity.

Keywords:

• bioaccumulation
• lipase enzyme
• optimisation
• Rhizopus delemar
• wastewater treatment