High-Yield Xylanase Production by a Newly Isolated Bacillus Cereus Strain Using Fed-Batch Cultivation and Agro-Industrial Waste Substrates

Xylanases are industrially significant enzymes, but their production can be challenging. This study aimed to isolate a native xylanase-producing bacterium and improve enzyme production through different cultivation strategies. Soil samples were collected from the Lavizan region of Tehran, Iran, for bacterial isolation and screening. The selected strain was identified as Bacillus cereus based on biochemical tests and 16S rRNA sequencing. Enzyme production was evaluated in batch culture, fed-batch culture with glucose supplementation, and media containing agro-industrial bran substrates. In batch fermentation, the B. cereus isolate showed a maximum xylanase activity of 155.4 IU/mL after 24 h. In the glucose-feeding experiment, a single addition of glucose to a final concentration of 2% (w/v) after 6 h increased the activity to 230.9 IU/mL, approximately 1.5-fold higher than the batch control. This experiment was performed in 50 mL culture volume in 250 mL flasks at 37 °C and 160 rpm, and all experiments were conducted in triplicate. The pH was not controlled during these flask experiments. In a separate batch-versus-fed-batch comparison using pure xylan, the fed-batch culture reached 222.0 IU/mL at 24 h. Barley bran was the most effective of the tested agro-industrial substrates, giving 133.2 IU/mL after 24 h, compared with 155.4 IU/mL for pure xylan. These results show that the selected strain can produce xylanase under the tested flask-scale conditions and that glucose supplementation and barley bran can be useful process variables for further optimization.