Late-stage cascade of oxidation reactions during the biosynthesis of oxalicine B in Penicillium oxalicum

Oxalicine B ( 1) is an α-pyrone meroterpenoid with a unique bispirocyclic ring system derived from Penicillium oxalicum. The biosynthetic pathway of 15-deoxyoxalicine B ( 4) was preliminarily reported in Penicillium canescens, however, the genetic base and biochemical characterization of tailoring reactions for oxalicine B ( 1) has remained enigmatic. In this study, we characterized three oxygenases from the metabolic pathway of oxalicine B ( 1), including a cytochrome P450 hydroxylase OxaL, a hydroxylating Fe(II)/α-KG-dependent dioxygenase OxaK, and a multifunctional cytochrome P450 OxaB. Intriguingly, OxaK can catalyze various multicyclic intermediates or shunt products of oxalicines with impressive substrate promiscuity. OxaB was further proven via biochemical assays to have the ability to convert 15-hydroxdecaturin A ( 3) to 1 with a spiro-lactone core skeleton through oxidative rearrangement. We also solved the mystery of OxaL that controls C-15 hydroxylation. Chemical investigation of the wild-type strain and deletants enabled us to identify 10 metabolites including three new compounds, and the isolated compounds displayed potent anti-influenza A virus bioactivities exhibiting IC50 values in the range of 4.0-19.9 μmol/L. Our studies have allowed us to propose a late-stage biosynthetic pathway for oxalicine B ( 1) and create downstream derivatizations of oxalicines by employing enzymatic strategies.

A comparison of refuse attenuation in laboratory and field scale lysimeters.

For this study, small and middle scale laboratory lysimeters, and a large scale field lysimeter in situ in Shanghai Refuse Landfill, with refuse weights of 187,600 and 10,800,000 kg, respectively, were created. These lysimeters are compared in terms of leachate quality (pH, concentrations of COD, BOD and NH3-N), refuse composition (biodegradable matter and volatile solid) and surface settlement for a monitoring period of 0-300 days. The objectives of this study were to explore both the similarities and disparities between laboratory and field scale lysimeters, and to compare degradation behaviors of refuse at the intensive reaction phase in the different scale lysimeters. Quantitative relationships of leachate quality and refuse composition with placement time show that degradation behaviors of refuse seem to depend heavily on the scales of the lysimeters and the parameters of concern, especially in the starting period of 0-6 months. However, some similarities exist between laboratory and field lysimeters after 4-6 months of placement because COD and BOD concentrations in leachate in the field lysimeter decrease regularly in a parallel pattern with those in the laboratory lysimeters. NH3-N, volatile solid (VS) and biodegradable matter (BDM) also gradually decrease in parallel in this intensive reaction phase for all scale lysimeters as refuse ages. Though the concrete data are different among the different scale lysimeters, it may be considered that laboratory lysimeters with sufficient scale are basically applicable for a rough simulation of a real landfill, especially for illustrating the degradation pattern and mechanism. Settlement of refuse surface is roughly proportional to the initial refuse height.