Samples, in form of two flasks containing 50 ml each, or 25 ml of broth in case of
bioreactor, were withdrawn at different times during the cultivation in a centrifugation
falcon tube (Falcon, USA). Immediately after sampling, the optical density was measured by
using spectrophotometer (DR/2500, Hach Co., Loveland, CO., USA) at 600 nm after proper
dilution. For all samples, the cultivated broth was diluted to give values less than (1 OD600)
for better accuracy. The OD of culture was converted to dry cell mass through a linear
correlation standard curve. Based on standard curve of this strain, One OD600 was almost
equivalent to 0.3 g/L.