Use of response surface methodology to enhance carotenoid pigment production from Cellulosimicrobium strain AZ

In the present study, the response surface methodology based on a rotatable central composite design was applied to optimize the production of the carotenoid pigment using a strain of Cellulosimicrobium that has not been reported so far for this genus. The microbial biomass and pigment production of strain AZ were investigated in the presence of tricarboxylic acid cycle intermediates (citrate, malate, succinate), and glutamate. Besides, the influence of the pH of the fermentation medium was also evaluated. The design consisted of a total of 32 experiments at five levels for each factor. Optimum carotenoid production (28.86 mg/L) was observed in the fermentation medium (pH 8.04) containing citrate (11.18 mM), glutamate (12.48 mM), malate (14.19 mM), and succinate (13.38 mM). It was 1.65-fold more than that of the OFAT method (17.5 mg/L) and 12-fold more than the unoptimized conditions (2.4 mg/L). The results were fitted with a quadratic model that could predict the responses to new observations significantly (pred-R-2=0.9686). Optimum microbial biomass (10.61 g/L) was observed in the presence of citrate (10.27 mM), glutamate (14.03 mM), malate (13.1 mM), and succinate (10.39 mM) as well as pH 8.36. In contrast to the results of one-factor-at-a-time, the carotenoid production had not a direct relationship with bacterial biomass. The established model could describe the variability of above 99.85% in the response based on the determination coefficient (R-2).