Screening, morphological and molecular characterization of fungi producing cystathionine γ-lyase.

The potency for production of cystathionine γ-lyase (CGL) by the fungal isolates was screened. Among the tested twenty-two isolates, Aspergillus carneus was the potent CGL producer (6.29 U/mg), followed by A. ochraceous (6.03 U/mg), A. versicolor (2.51 U/mg), A. candidus (2.12 U/mg), A. niveus and Penicillium notatum (2.0 U/mg). The potent six isolates producing CGL was characterized morphologically, A. carneus KF723837 was further molecularly characterized based on the sequence of 18S-28S rDNA. Upon sulfur starvation, the yield of A. carneus extracellular CGL was increased by about 1.7- and 4.1-fold comparing to non-sulfur starved and L-methionine free medium, respectively. Also, the uptake of L-methionine was duplicated upon sulfur starvation, assuming the activation of specific transporters for L-methionine and efflux of CGL. Also, the intracellular thiols and GDH activity of A. carneus was strongly increased by S starvation, revealing the activation of in vivo metabolic antioxidant systems. Upon irradiation of A. carneus by 2.0 kGy of γ-rays, the activity of CGL was increased by two-fold, regarding to control, with an obvious decreases on its yield upon further doses. Practically, CGL activity from the solid A. carneus cultures, using rice bran as substrate, was increased by 1.2-fold, comparing to submerged cultures, under optimum conditions.