Evaluation of low-intensity laser radiation on stimulating the cholesterol degrading activity of Streptomyces fradiae. Part II: Optimization of environmental and nutritional factors

A previous investigation was carried out concerning the isolation of bacteria and fungi having ability to decompose cholesterol from different cholesterol-rich sources. Streptomyces fradiae was identified as the most potent degrading isolate. In a trail to increase the cholesterol decomposing potentiality of S. fradiae, low intensity Nd-YAG laser irradiation was evaluated. The exposure of the chlorophyllin-photosensitized bacterium to 210 mW Ne-YAG laser for 8 min induced significant increase in cholesterol degrading activity reaching 73.8% as compared with 54.2% in the case of non-irradiated, non-photosensitized culture. The optimization of environmental conditions and nutritional factors of the irradiated bacterium was carried out and aimed to maximize cholesterol decomposition. The following optimas were recorded for irradiated and non-irradiated S. fradiae: substrate concentration 1–1.5 as compared to 1.0 g/l; yeast extract, 4–6 as compared to 5–6 g/l; magnesium nitrate and ammonium nitrate as nitrogen source for both bacteria; glucose concentration, 10–20 as compared to 10 g/l; incubation period, 6 days for both; incubation temperature, 30–35 °C as compared to 30 °C; pH, 7–8 as compared to 7; and shaking speed, 40–120 as compared with 80 rpm, respectively. Under all optimized conditions, the cholesterol decomposing activity of irradiated photosensitized S. fradiae (88.5%) exceeds the activity of the non-irradiated one (78.7%). Moreover, the irradiated bacterium was able to keep its optimas over a wider range of substrate, yeast extract, glucose, temperature, pH, and shaking as compared the non-irradiated one.