Tetracycline pollution is a growing global threat to aquatic and terrestrial biodiversity due to its unprecedented use in aquaculture, livestock, and human disease prevention. The influx of tetracycline may annihilate the microbial ecology structure in the environment and pose a severe threat to humans by disturbing the food chain. Although significant research data are available in the literature on various aspects of tetracycline, including detection techniques, degradation mechanisms, degradation products, and policy statements to curtail the issue, there is a scarcity of a report to compile the recent data in the literature for better analysis and comparison by the policymakers. To achieve this paucity in knowledge, the current study aims at collecting data on the available degradation strategies, mechanisms involved in biodegradable and non-biodegradable routes, the main factor affecting degradation strategies, compile novel detection techniques of tetracycline antibiotics in the environment, discuss antibiotic resistance genes and their potential role in degradation. Finally, limitations in the current bioremediation techniques and the future prospects are discussed with pointers for the decision-makers for a safer environment.

The biorefining technology for biofuels and chemicals from lignocellulosic biomass has made great progress in the world. However, mobilization of laboratory research toward industrial setup needs to meet a series of criteria, including the selection of appropriate pretreatment technology, breakthrough in enzyme screening, pathway optimization, and production technology, etc. Extremophiles play an important role in biorefinery by providing novel metabolic pathways and catalytically stable/robust enzymes that are able to act as biocatalysts under harsh industrial conditions on their own. This review summarizes the potential application of thermophilic, psychrophilic alkaliphilic, acidophilic, and halophilic bacteria and extremozymes in the pretreatment, saccharification, fermentation, and lignin valorization process. Besides, the latest studies on the engineering bacteria of extremophiles using metabolic engineering and synthetic biology technologies for high-efficiency biofuel production are also introduced. Furthermore, this review explores the comprehensive application potential of extremophiles and extremozymes in biorefinery, which is partly due to their specificity and efficiency, and points out the necessity of accelerating the commercialization of extremozymes.

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Laccase is essential for the biodepolymerization of lignin, but the challenge is that the reaction mechanism has not been fully elucidated. The laccase (Lacc) inactivated mutant of Bacillus ligniniphilus L1 had a sharp decline in its ability to degrade lignin, which proved its indispensable role in lignin depolymerization. The purified Lacc from recombinant Escherichia coli BL21 and its mediator system (LMS) displayed significant lignin degradation capacities as well as remarkable thermotolerance and solvent resistance. The chemical oxygen demand removal rates of LMS for alkaline and milled wood lignin have reached 67.0% and 80.9%, respectively. Comprehensive analyses, including Fourier-transform infrared spectrometry, gas chromatography–mass spectrometry, 2D-HSQC-NMR, and time-of-flight secondary ion mass spectrometry, unveiled that Lacc- and LMS-oxidized lignin include at least 10 or more catalytic reactions. Lacc can effectively degrade G-lignin even without a mediator, and the removal rate of G-lignin is higher than that of S-lignin. In addition, the supplementation of the mediator increased the removal rate of H-lignin by Lacc and the cleavage of interunit linkages such as β-O-4, β-5, β-β, 4-O-5, and 5-5. Moreover, we found that Lacc cannot polymerize some aromatic monomers into dimers or polymers, which is different from fungal and plant laccases. It is by far the most detailed study describing the reaction mechanism of lignin oxidation by bacterial laccase. These results provide new insights into the catalytic mechanism of bacterial laccase and lay the foundation for the application of laccase in lignin valorization.

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