Lei Wang,Mengdi Liang,Yang Fang,Jun Yin,Jungang Jiang,Yifan Zhang,Haiping Yang
Understanding the pyrolysis mechanism of native lignin is essential for improving the conversion efficiency of fast pyrolysis technology. However, due to the complex and various nature of lignin interunit linkages, the pyrolysis mechanism of lignin has not been clearly revealed so far, especially for native lignin. In this work, two types of guaiacyl-dehydrogenation polymers (G-DHPs) were synthesized using two different methods in vitro , namely endwise polymerization (G-DHPs-endwise) and bulk polymerization (G-DHPs-bulk), which were used as native lignin models. The chemical structures of the synthesized G-DHPs along with natural G-lignin ( i.e., milled wood lignin, MWL) were analyzed by using 2D HSQC NMR, and their pyrolysis characteristics were investigated by using a fixed bed reactor . In comparison with G-DHPs-bulk, G-DHPs-endwise had more similar structure and pyrolysis characteristics with that of MWL, which suggested that G-DHPs-endwise was a more suitable model for G-type lignin. Further mechanical study revealed that the pyrolysis of G-DHPs-endwise underwent an end-breaking pathway, by which the branched carbon of the coniferyl alcohol structure ends were cleaved at the early stage to depolymerize into guaiacol . This study can thus enhance the understanding of the thermal depolymerization of native lignin and provide the evidence for revealing pyrolysis mechanism.
2(S)-dihydroxypropanesulfonate (DHPS) is a microbial degradation product of 6-deoxy-6-sulfo-d-glucopyranose (sulfoquinovose), a component of plant sulfolipid with an estimated annual production of 1010 tons. DHPS is also at millimolar levels in highly abundant marine phytoplankton. Its degradation and sulfur recycling by microbes, thus, play important roles in the biogeochemical sulfur cycle. However, DHPS degradative pathways in the anaerobic biosphere are not well understood. Here, we report the discovery and characterization of two O2-sensitive glycyl radical enzymes that use distinct mechanisms for DHPS degradation. DHPS-sulfolyase (HpsG) in sulfate- and sulfite-reducing bacteria catalyzes C–S cleavage to release sulfite for use as a terminal electron acceptor in respiration, producing H2S. DHPS-dehydratase (HpfG), in fermenting bacteria, catalyzes C–O cleavage to generate 3-sulfopropionaldehyde, subsequently reduced by the NADH-dependent sulfopropionaldehyde reductase (HpfD). Both enzymes are present in bacteria from diverse environments including human gut, suggesting the contribution of enzymatic radical chemistry to sulfur flux in various anaerobic niches.
Sulfonamides, as broad-spectrum antibiotics, are widely used to protect against bacterial infections in livestock production. A large number of sulfa antibiotics are discharged into soil and water system, which poses a great threat to the safety of organisms. The antibacterial mechanism of sulfonamides is to prevent folate biosynthesis by competitively inhibiting bacterial dihydropteroate synthetase (DHPS). The inhibitory effect of sulfanilamide on root growth has been reported, but the mechanism has not been determined. Here, we used high performance liquid chromatography with ultraviolet detector (HPLC-UV) and transgenic technology to study the effect of sulfonamides on folate synthesis in plants. The results showed that the application of sulfonamide sharply reduced the content of folic acid in plants, resulting in strong inhibition of cell division in the root apical meristem. The inhibition of sulfonamide on cell division can be relieved by supplementing synthetic folic acid and folinic calcium salt hydrate. The transgenic plants expressing the bacterial antibiotic resistance genes (ARGs) Sul1 or Sul2 showed obvious antibiotic resistance. Taking these results together, we suggest that sulfonamides repress cell proliferation in the root apical meristem by competitively inhibiting the biosynthesis of folic acid in plants.
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