Biotransformation of quercetin by Gliocladium deliquescens NRRL 1086 / 中国天然药物

With an attempt to synthesize high-value isoquercitrin (quercetin-3-O-β-D-glucopyranoside), we carried out the biotransformation of quercetin (1) by Gliocladium deliquescens NRRL 1086. Along with the aimed product quercetin 3-O-β-D-glycoside (2), three additional metabolites, 2-protocatechuoyl-phlorogucinol carboxylic acid (3), 2,4,6-trihydroxybenzoic acid (4), and protocatechuic acid (5), were also isolated. The time-course experiments revealed that there were two metabolic routes, regio-selectivity glycosylation and quercetin 2,3-dioxygenation, co-existing in the culture. Both glycosylation and oxidative cleavage rapidly took place after quercetin feeding; about 98% quercetin were consumed within the initial 8 h and the oxdized product (2-protocatechuoyl-phlorogucinol carboxylic acid) was hydrolyzed into two phenolic compounds (2,4,6-trihydroxybenzoic acid and protocatechuic acid). We also investigated the impact of glucose content and metal ions on the two reactions and found that high concentrations of glucose significantly inhibited the oxidative cleavage and improved the yield of isoquercitrin and that Ca, Fe, Mn, Mg, and Zn inhibited glycosylation. To test the promiscuity of this culture, we selected other four flavonols as substrates; the results demonstrated its high regio-selectivity glycosylation ability towards flavonols at C-3 hydroxyl. In conclusion, our findings indicated that the versatile microbe of G. deliquescens NRRL 1086 maitained abundant enzymes, deserving further research.

BEAUVERIA BASSIANA: quercetinase production and genetic diversity

Beauveria bassiana genetic diversity and ability to synthesize quercetin 2,3-dioxygenase (quercetinase) were analyzed. B. bassiana isolates, obtained from Brazilian soil samples, produced quercetinase after induction using 0.5 g/L quercetin. B. bassiana ATCC 7159 (29.6 nmol/mL/min) and isolate IP 11 (27.5 nmol/ml/min) showed the best performances and IP 3a (9.5 nmol/mL/min) presented the lowest level of quercetinase activity in the culture supernatant. A high level of polymorphism was detected by random amplified polymorphic DNA (RAPD) analysis. The use of internal-transcribed-spacer ribosomal region restriction fragment length polymorphism (ITS-RFLP) did not reveal characteristic markers to differentiate isolates. However, the ITS1-5.8S-ITS2 region sequence analysis provided more information on polymorphism among the isolates, allowing them to be clustered by relative similarity into three large groups. Correlation was tested according to the Person's correlation. Data of our studies showed, that lower associations among groups, level of quercetinase production, or geographical origin could be observed. This study presents the production of a novel biocatalyst by B. bassiana and suggests the possible industrial application of this fungal species in large-scale biotechnological manufacture of quercetinase.