Mutation of Candida tropicalis by Irradiation with a He-Ne Laser To Increase Its Ability To Degrade Phenol

Abstract

Candida tropicalis isolated from acclimated activated sludge was used in this study. Cell suspensions with 5 ؋ 10 7 cells ml ؊1 were irradiated by using a He-Ne laser. After mutagenesis, the irradiated cell suspension was diluted and plated on yeast extract-peptone-dextrose (YEPD) medium. Plates with approximately 20 individual colonies were selected, and all individual colonies were harvested for phenol biodegradation. The phenol biodegradation stabilities for 70 phenol biodegradation-positive mutants, mutant strains CTM 1 to 70, ranked according to their original phenol biodegradation potentials, were tested continuously during transfers. Finally, mutant strain CTM 2, which degraded 2,600 mg liter ؊1 phenol within 70.5 h, was obtained on the basis of its capacity and hereditary stability for phenol biodegradation. The phenol hydroxylase gene sequences were cloned in wild and mutant strains. The results showed that four amino acids were mutated by irradiation with a laser. In order to compare the activity of phenol hydroxylase in wild and mutant strains, their genes were expressed in Escherichia coli BL21(DE3) and enzyme activities were spectrophotometrically determined. It was clear that the activity of phenol hydroxylase was promoted after irradiation with a He-Ne laser. In addition, the cell growth and intrinsic phenol biodegradation kinetics of mutant strain CTM 2 in batch cultures were also described by Haldane's kinetic equation with a wide range of initial phenol concentrations from 0 to 2,600 mg liter ؊1 . The specific growth and degradation rates further demonstrated that the CTM 2 mutant strain possessed a higher capacity to resist phenol toxicity than wild C. tropicalis did.

Growth of Trametes versicolor on phenol

“…In this study, the emphasis was laid on its ability to utilize phenol as a sole carbon and energy source. It has been reported that the fungal metabolism of aromatic compounds occur via orthoWssion pathway [1,7]. The phenol hydroxylase (EC 1.14.13.7) and cis,cis-muconate lactonase (EC 5.5.1.1) are key enzymes in this catabolic process.…”

Inorganic impurity removal from waste oil and wash-down water by Acinetobacter johnsonii

“…Cell density was monitored spectrophotometrically by measuring the optical density at 600 nm [27]. Inorganic impurity in oil was determined by the standard Petroleum Products and Additives-Determination of Mechanical Impurities-Gravimetric Method (GB/T 511-2010).…”

Mutation breeding of Bacillus subtilis YTB4 with high yield of multienzyme complex

“…The irradiation condition was varied by adjusting output power (15 mW) and exposure time (5, 10, 15, 20, 25 and 30 min) (Kohli and Gupta, 2003). The laser output power was set to 15 mW and 0.2 ml of bacterial suspension was placed in sterile test tubes and located at 30 cm under the laser for different laser exposure time (Jiang et al, 2007). After mutagenesis, bacterial suspension with serial dilutions was prepared, and three 0.1 ml parallel samples were taken out from each dilution.…”