Five-factor-at-a-time (FFAT) approach for optimal production of an extracellular RNase from Bacillus safensis RB-5

A Gram-positive, rod-shaped, endospore-forming, and RNA-degrading bacterium RB-5 was isolated from a soil sample. Based on 16-rDNA gene sequence, the bacterium RB-5 was identified as Bacillus safensis (Accession number KX443714.1). The bacterium appeared to be related to Bacillus safensis KL-052, an other-member of genus Bacillus. One-factor-at-a-time (OFAT) and Response Surface Methodology (RSM) statistical approaches were used to optimize the fermentation broth to obtain an improved extracellular RNase production from B. safensis RB-5. These approaches improved RNase activity of B. safensis KL-052 from 4.26 to 7.85 U/mL. The OFAT approach was used to study the effects of supplementation of carbon, nitrogen and physical conditions, which included temperature, pH and agitation rate on extracellular RNase production by B. safensis KL-052. Five variables screened by Central Composite Design (CCD) were employed to evaluate their interactive effects on RNase production by the organism. CCD selected 2⁵ factorial values obtained by the statistical approach were peptone 1.13% (w/v), sodium nitrate 1.13% (w/v), MgSO₄ 0.06% (w/v), pH 8.5, and temperature 35 °C for RNase production by B. safensis. The highest predicted value of RNase was 7.05 U/ml while actual obtained value was 7.85 U/ml that was ∼84% and 1.84-fold higher than OFAT approach.