Pretreatment is the key step to overcome the recalcitrance of lignocellulosic biomass making sugars available for subsequent enzymatic hydrolysis and microbial fermentation. During the process of pretreatment and enzymatic hydrolysis as well as fermentation, various toxic compounds may be generated with strong inhibition on cell growth and the metabolic capacity of fermenting strains. Zymomonas mobilis is a natural ethanologenic bacterium with many desirable industrial characteristics, but it can also be severely affected by lignocellulosic hydrolysate inhibitors. In this review, analytical methods to identify and quantify potential inhibitory compounds generated during lignocellulose pretreatment and enzymatic hydrolysis were discussed. The effect of hydrolysate inhibitors on Z. mobilis was also summarized as well as corresponding approaches especially the high-throughput ones for the evaluation. Then the strategies to enhance inhibitor tolerance of Z. mobilis were presented, which include both forward and reverse genetics approaches such as classical and novel mutagenesis approaches, adaptive laboratory evolution, as well as genetic and metabolic engineering. Moreover, this review provided perspectives and guidelines for future developments of robust strains for efficient bioethanol or biochemical production from lignocellulosic materials.
Nanozymes are considered as ideal substitutes for nature enzymes; however, the enzyme activity and the relevant detection sensitivity in actual samples still need to be further improved. Here, a nanomaterial of CuO NP-POM composed of polyoxometalate (POM) decorated with copper oxide nanoparticles (CuO NPs), which possessed tetraenzyme mimetic activities including oxidase (OXD)-, peroxidase (POD)-, catalase (CAT)-, and glutathione peroxidase (GPx)-like activities was developed. The corresponding catalytic performances, mechanisms, and kinetics were systematically investigated. Based on the POD-like activity of a CuO NP-POM nanocomposite, a colorimetric sensing platform for ascorbic acid (AA) was built with the detection limit of 15 nM, depending on the fact that AA can efficiently react with the oxidation product of TMB, which was catalyzed by CuO NP-POM on the basis of the POD-like activity. A simple fluorometric sensor for Fe 2+ was developed on the basis of the GPx-like activity of CuO NP-POM with the detection limit of 8.0 nM. CuO NP-POM can weaken the fluorescence of the isoindole derivative derived from GSH and o-phthalaldehyde (OPA) due to the excellent GPx-like activity, which can accelerate the catalysis of GSH into GSSG in the presence of H 2 O 2 . However, in the presence of Fe 2+ , the fluorescence was recovered owing to the fact that the Fenton reaction between Fe 2+ and H 2 O 2 could reduce GSSG into GSH. The proposed colorimetric and fluorometric sensors have been successfully applied in detecting AA and Fe 2+ in several food and biological samples. This work not only developed a nanocomposite with enhanced multinanozyme activity but also offered rapidly detection methods for the analysis of specific targets via the special nanozyme activities.
A series of CuZnAl oxide-composite catalysts were prepared via decomposition of CuZnAl hydrotalcite-like compounds (HTLcs). The catalysts derived from CuZnAl HTLcs (Cu: 37%, Zn: 15%, Al: 48% mol; using metal nitrate or acetate precursors) at 600 C provided excellent activity and stability for the methanol steam reforming. CuZnAl HTLcs were almost decomposed completely at 600 C to form highly dispersed CuO with large specific surface area while forming CuAl 2 O 4 spinel that played a key role in separating and stabilizing the nano-sized Cu and ZnO during the reaction. The CuZnAl catalyst prepared from metal acetates could highly convert H 2 O/MeOH (1.3/1, mol/mol) mixture into hydrogen with only $0.05% CO at 250 C or $0.005% at 210 C. It is evidenced that the former afforded stronger Cu-ZnO interaction, which might be the intrinsic reason for the significant promotion of catalyst selectivity.
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