Critical Reviews in Biotechnology最新文献

Compounds containing chiral C-N bonds play a vital role in the composition of biologically active natural products and small pharmaceutical molecules. Therefore, the development of efficient and convenient methods for synthesizing compounds containing chiral C-N bonds is a crucial area of research. Nicotinamide-dependent oxidoreductases (NDOs) emerge as promising biocatalysts for asymmetric synthesis of chiral C-N bonds due to their mild reaction conditions, exceptional stereoselectivity, high atom economy, and environmentally friendly nature. This review aims to present the structural characteristics and catalytic mechanisms of various NDOs, including imine reductases/ketimine reductases, reductive aminases, EneIRED, and amino acid dehydrogenases. Additionally, the review highlights protein engineering strategies employed to modify the stereoselectivity, substrate specificity, and cofactor preference of NDOs. Furthermore, the applications of NDOs in synthesizing essential medicinal chemicals, such as noncanonical amino acids and chiral amine compounds, are extensively examined. Finally, the review outlines future perspectives by addressing challenges and discussing the potential of utilizing NDOs to establish efficient biosynthesis platforms for C-N bond synthesis. In conclusion, NDOs provide an economical, efficient, and environmentally friendly toolbox for asymmetric synthesis of C-N bonds, thus contributing significantly to the field of pharmaceutical chemical development.

Owing to the increasing worldwide population explosion, managing waste generated from the food sector has become a cross-cutting issue globally, leading to environmental, economic, and social issues. Circular economy-inspired waste valorization approaches have been increasing steadily, generating new business opportunities developing valuable bioproducts using food waste, especially fruit wastes, that may have several applications in energy-food-pharma sectors. Dragon fruit waste is one such waste resource, which is rich in several value-added chemicals and oils, and can be a renewable resource to produce several value-added compounds of potential applications in different industries. Pretreatment and extraction processes in biorefineries are important strategies for recovering value-added biomolecules. There are different methods of valorization, including green extractions and biological conversion approaches. However, microbe-based conversion is one of the advanced technologies for valorizing dragon fruit waste into bioethanol, bioactive products, pharmaceuticals, and other valued products by reusing or recycling them. This state-of-the-art review briefly overviews the dragon fruit waste management strategies and advanced eco-friendly and cost-effective valorization technologies. Furthermore, various applications of different valuable bioactive components obtained from dragon fruit waste have been critically discussed concerning various industrial sectors. Several industrial sectors, such as food, pharmaceuticals, and biofuels, have been critically reviewed in detail.

Flavonoids and their methylated derivatives have immense market potential in the food and biomedical industries due to their multiple beneficial effects, such as antimicrobial, anti-inflammatory, and anticancer activities. The biological synthesis of flavonoids and their derivatives is often accomplished via the use of genetically modified microorganisms to ensure large-scale production. Therefore, it is pivotal to understand the properties of O-methyltransferases (OMTs) that mediate the methylation of flavonoids. However, the properties of these OMTs are governed by their: sources, substrate specificity, amino acid residues in the active sites, and the intricate mechanism. In order to obtain a clue for the selection of suitable OMTs for the biosynthesis of a target methylated flavonoid, we made a comprehensive review of the currently reported results, with a particular focus on their comparative regioselectivity for different flavonoid substrates. Additionally, the possible mechanisms for the diversity of this class of enzymes were explored using molecular simulation technology. Finally, major gaps in our understanding and areas for future studies were discussed. The findings of this study may be useful in selecting genes that encode OMTs and designing enzyme-based processes for synthesizing O-methylated flavonoids.

Shotgun metagenomics is an increasingly cost-effective approach for profiling environmental and host-associated microbial communities. However, due to the complexity of both microbiomes and the molecular techniques required to analyze them, the reliability and representativeness of the results are contingent upon the field, laboratory, and bioinformatic procedures employed. Here, we consider 15 field and laboratory issues that critically impact downstream bioinformatic and statistical data processing, as well as result interpretation, in bacterial shotgun metagenomic studies. The issues we consider encompass intrinsic properties of samples, study design, and laboratory-processing strategies. We identify the links of field and laboratory steps with downstream analytical procedures, explain the means for detecting potential pitfalls, and propose mitigation measures to overcome or minimize their impact in metagenomic studies. We anticipate that our guidelines will assist data scientists in appropriately processing and interpreting their data, while aiding field and laboratory researchers to implement strategies for improving the quality of the generated results.

Oral fungal infections pose a threat to human health and increase the economic burden of oral diseases by prolonging and complicating treatment. A cost-effective strategy is to try to prevent these infections from happening in the first place. With this purpose, biomaterials with antifungal properties are a crucial element to overcome fungal infections in the oral cavity. In this review, we go through different kinds of biomaterials and coatings that can be used to functionalize them. We also review their potential as a therapeutic approach in addition to prophylaxis, by going through traditional and alternative antifungal compounds, e.g., essential oils, that could be incorporated in them, to enhance their efficacy against fungal pathogens. We aim to highlight the potential of these technologies and propose questions that need to be addressed in prospective research. Finally, we intend to concatenate the key aspects and technologies on the use of biomaterials in oral health, to create an easy to find summary of the current state-of-the-art for researchers in the field.

The generation of food waste (FW) is increasing at an alarming rate, contributing to a total of 32% of all the waste produced globally. Anaerobic digestion (AD) is an effective method for dealing with organic wastes of various compositions, like FW. Waste valorization into value-added products has increased due to the conversion of FW into biogas using AD technology. A variety of pathways are adopted by microbes to avoid unfavorable conditions in AD, including competition between sulfate-reducing bacteria and methane (CH₄)-forming bacteria. Anaerobic bacteria decompose organic matter to produce biogas, a digester gas. The composition depends on the type of raw material and the method by which the digestion process is conducted. Studies have shown that the biogas produced by AD contains 65-75% CH₄ and 35-45% carbon dioxide (CO₂). Methanothrix soehngenii and Methanosaeta concilii are examples of species that convert acetate to CH₄ and CO₂. Methanobacterium bryantii, Methanobacterium thermoautotrophicum, and Methanobrevibacter arboriphilus are examples of species that produce CH₄ from hydrogen and CO₂. Methanobacterium formicicum, Methanobrevibacter smithii, and Methanococcus voltae are examples of species that consume formate, hydrogen, and CO₂ and produce CH₄. The popularity of AD has increased for the development of biorefinery because it is seen as a more environmentally acceptable alternative in comparison to physico-chemical techniques for resource and energy recovery. The review examines the possibility of using accessible FW to produce important value-added products such as organic acids (acetate/butyrate), biopolymers, and other essential value-added products.

Exponential increasing demands for base metals have made meaningful processing of their quite low-grade (>1%) resources. Froth flotation is the most important physicochemical pretreatment technique for processing low-grade sulfide ores. In other words, flotation separation can effectively upgrade finely liberated base metal sulfides based on their surface properties. Various sulfide surface characters can be modified by flotation surfactants (collectors, activators, depressants, pH regulators, frothers, etc.). However, these reagents are mostly toxic. Therefore, using biodegradable flotation reagents would be essential for a green transition of ore treatment plants, while flotation circuits deal with massive volumes of water and materials. Pyrite, the most abundant sulfide mineral, is frequently associated with valuable minerals as a troublesome gangue. It causes severe technical and environmental difficulties. Thus, pyrite should be removed early in the beneficiation process to minimize its problematic issues. Recently, conventional inorganic pyrite depressants (such as cyanide, lime, and sulfur-oxy compounds) have been successfully assisted or even replaced with eco-friendly and green reagents (including polysaccharide-based substances and biodegradable acids). Yet, no comprehensive review is specified on the biodegradable acid depression reagents (such as tannic, lactic, humic acids, etc.) for pyrite removal through flotation separation. This study has comprehensively reviewed the previously conducted investigations in this area and provides suggestions for future assessments and developments. This robust review has systematically explored depression performance, various adsorption mechanisms, and aspects of these reagents on pyrite surfaces. Furthermore, factors affecting their efficiency were analyzed, and gaps within each area were highlighted.

After conventional oil recovery operations, more than half of the crude oil still remains in a form, which is difficult to extract. Therefore, exploring and developing new enhanced oil recovery (EOR) technologies have always been priority research in oilfield development. Microbial enhanced oil recovery (MEOR) is a promising tertiary oil recovery technology that has received widespread attention from the global oil industry in recent years due to its environmental friendliness, simplicity of operation, and cost-effectiveness. This review presents the: principle, characteristics, classification, recent development, and applications of MEOR technology. Based on hundreds of field trials conducted worldwide, the microbial strains, nutrient systems, and actual effects used in these technologies are summarized, with an emphasis on the achievements made in the development and application of MEOR in China in recent years. These technical classifications involve: microbial huff and puff recovery (MHPR), microbial flooding recovery (MFR), microbial selective plugging recovery (MSPR), and microbial wax removal and control (MWRC). Most of them have achieved good results, with a success rate of approximately 80%. These successful cases have accumulated into rich experiential indications for the popularization and application of MEOR technology, but there are still important yet uncertain factors that hinder the industrialization of this technology. Finally, based on the extensive research and development of MEOR by the authors, especially in both laboratory and industrial large scales, the main challenges and future perspectives of the industrial application for MEOR are presented.

Natural astaxanthin is synthesized by diverse organisms including: bacteria, fungi, microalgae, and plants involving complex cellular processes, which depend on numerous interrelated parameters. Nonetheless, existing knowledge regarding astaxanthin biosynthesis and the conditions influencing astaxanthin accumulation is fairly limited. Thus, manipulation of the growth conditions to achieve desired biomass and astaxanthin yields can be a complicated process requiring cost-intensive and time-consuming experiment-based research. As a potential solution, modeling and simulation of biological systems have recently emerged, allowing researchers to predict/estimate astaxanthin production dynamics in selected organisms. Moreover, mathematical modeling techniques would enable further optimization of astaxanthin synthesis in a shorter period of time, ultimately contributing to a notable reduction in production costs. Thus, the present review comprehensively discusses existing mathematical modeling techniques which simulate the bioaccumulation of astaxanthin in diverse organisms. Associated challenges, solutions, and future perspectives are critically analyzed and presented.

Astaxanthin is a naturally occurring xanthophyll with powerful: antioxidant, antitumor, and antibacterial properties that are widely employed in food, feed, medicinal and nutraceutical industries. Currently, chemical synthesis dominates the world's astaxanthin market, but the increasing demand for natural products is shifting the market for natural astaxanthin. Haematococcus pluvialis (H. pluvialis) is the factory source of natural astaxanthin when grown in optimal conditions. Currently, various strategies for the production of astaxanthin have been proposed or are being developed in order to meet its market demand. This up-to-date review scrutinized the current approaches or strategies that aim to increase astaxanthin yield from H. pluvialis. We have emphasized the genetic and environmental parameters that increase astaxanthin yield. We also looked at the transcriptomic dynamics caused by environmental factors (phytohormones induction, light, salt, temperature, and nutrient starvation) on astaxanthin synthesizing genes and other metabolic changes. Genetic engineering and culture optimization (environmental factors) are effective approaches to producing more astaxanthin for commercial purposes. Genetic engineering, in particular, is accurate, specific, potent, and safer than conventional random mutagenesis approaches. New technologies, such as CRISPR-Cas9 coupled with omics and emerging computational tools, may be the principal strategies in the future to attain strains that can produce more astaxanthin. This review provides accessible data on the strategies to increase astaxanthin accumulation natively. Also, this review can be a starting point for new scholars interested in H. pluvialis research.