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).

In the present study, the effect of various fermentation media on the production of carotenoid pigment in a radiation-resistant strain of Dietzia maris was reported. The biomass and pigment production of this strain was evaluated using various sources of carbon and nitrogen as well as different concentrations of whey medium. The antioxidant and cytotoxic activities of the extracted pigment were also determined using ferric reducing antioxidant power (FRAP), 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH), and MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assays. The antibacterial activity of the carotenoid pigment was also evaluated. All carbon sources increased the pigment production of D. maris in the following order: glucose > raffinose = starch = xylose > sorbitol > sucrose. However, only glucose, xylose, and sorbitol significantly increased the microbial biomass as compared to the control. Moreover, all organic nitrogen sources and ammonium sulfate enhanced the pigment production of the studied strain by approximately 6–9 folds. The free radical scavenging capacity and FRAP of the D. maris carotenoid extract were reported as half-maximal effective concentration or EC 50 = 3.30 mg/ml and EC 50 =28.46 μg/ml, respectively. The maximum amount of biomass and carotenoid pigment produced by D. maris was obtained in the fermentation medium containing 1 g/l glucose and 1 g/l yeast extract (18 mg/l). This strain can be considered as a promising biocatalyst for the commercial production of natural carotenoids due to its antioxidant capacity and noncytotoxic activity.