Effect of Fe NPs on the growth rate and biosurfactant production by Nocardiopsis MSA13A. Lag period was fall on 0 to 2 d which is not shown in the Figure. The growth rate was presented in terms of percent increase over the control. Growth rate was derived from colony plate count and OD values. 10 mg/L Fe NPs induced growth rate of Nocardiopsis MSA13A to the maximum of 67% over control. The same Fe NPs concentration increased to 80% biosurfactant production over control.