Optimizing bioconversion of ferulic acid to vanillin by Bacillus subtilis in the stirred packed reactor using Box-Behnken design and desirability function

Pathway-Adapted Biosensor for High-Throughput Screening of O-Methyltransferase and its Application in Vanillin Synthesis

Vanillin is a widely used flavoring compound in the food, pharmaceutical, and cosmetics area. However, the biosynthesis of vanillin from low-cost shikimic acid is significantly hindered by the low activity of the rate-limiting enzyme, caffeate O-methyltransferase (COMT). To screen COMT variants with improved conversion rates, we designed a biosensing system that is adaptable to the COMT-mediated vanillin synthetic pathway. Through the evolution of aldehyde transcriptional factor YqhC, we obtained a dual-responsive variant, MuYqhC, which positively responds to the product and negatively responds to the substrate, with no response to intermediates. Using the MuYqhC-based vanillin biosensor, we successfully identified a COMT variant, Mu176, that displayed a 7-fold increase in the conversion rate compared to the wild-type COMT. This variant produced 2.38 mM vanillin from 3 mM protocatechuic acid, achieving a conversion rate of 79.33%. The enhanced activity of Mu176 was attributed to an enlarged binding pocket and strengthened substrate interaction. Applying Mu176 to Bacillus subtilis increased the level of vanillin production from shikimic acid by 2.39-fold. Further optimization of the production chassis, increasing the S-adenosylmethionine supply and the precursor concentration, elevated the vanillin titer to 1 mM, marking the highest level of vanillin production from shikimic acid in Bacillus. Our work highlights the significance of the MuYqhC-based biosensing system and the Mu176 variant in vanillin production.

Microbial valorization of lignin: Prospects and challenges

Lignin is the world's second most prevalent biomaterial, but its effective value-added product valorization methods are still being developed. The most common preparation processes for converting lignin to platform chemicals and biofuels are fragmentation and depolymerization. Due to its structural diversity, fragmentation generally produces a variety of products, necessitating tedious separation and purifying methods to isolate the desired products. Bacterial-based techniques are commonly utilized for lignin fragmentation due to their high metabolitic activity. Recent advancements in lignin valorization utilizing bacteria, such as lignin decomposing microbes and major pathways involved that can breakdown lignin into various valuable products namely lipids, furfural, vanillin, polyhydroxybutyrate, poly lactic acid blends were discussed in this review. This review also covers the genetic and fermentation methodologies to enhance lignin decomposition, challenges and future trends of microbe based lignin valorization.

Novel Cold-Adapted Recombinant Laccase KbLcc1 from Kabatiella bupleuri G3 IBMiP as a Green Catalyst in Biotransformation

Cold-adapted enzymes are useful tools in the organic syntheses conducted in mixed aqueous-organic or non-aqueous solvents due to their molecular flexibility that stabilizes the proteins in low water activity environments. A novel psychrophilic laccase gene from Kabatiella bupleuri, G3 IBMiP, was spliced by Overlap-Extension PCR (OE-PCR) and expressed in Pichia pastoris. Purified recombinant KbLcc1 laccase has an optimal temperature of 30 °C and pH of 3.5, 5.5, 6.0, and 7.0 in the reaction with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), guaiacol, sinapic acid, and syringaldazine, respectively. Moreover, laccase KbLcc1 is highly thermolabile, as it loses 40% of activity after 30 min at 40 °C and is inactivated at 50 °C after the same period of incubation. The new enzyme remained active with 1 mM of Ni2+, Cu2+, Mn2+, and Zn2+ and with 2 mM of Co2+, Ca2+, and Mg2+, but Fe2+ greatly inhibited the laccase activity. Moreover, 1% ethanol had no impact on KbLcc1, although acetone and ethyl acetate decreased the laccase activity. The presence of hexane (40%, v/v) caused a 58% increase in activity. Laccase KbLcc1 could be applied in the decolorization of synthetic dyes and in the biotransformation of ferulic acid to vanillin. After 5 days of reaction at 20 °C, pH 3.5, with 1 mM ABTS as a mediator, the vanillin concentration was 21.9 mg/L and the molar yield of transformation reached 14.39%.

Advances in engineered Bacillus subtilis biofilms and spores, and their applications in bioremediation, biocatalysis, and biomaterials

Bacillus subtilis is a commonly used commercial specie with broad applications in the fields of bioengineering and biotechnology. B. subtilis is capable of producing both biofilms and spores. Biofilms are matrix-encased multicellular communities that comprise various components including exopolysaccharides, proteins, extracellular DNA, and poly-γ-glutamic acid. These biofilms resist environmental conditions such as oxidative stress and hence have applications in bioremediation technologies. Furthermore, biofilms and spores can be engineered through biotechnological techniques for environmentally-friendly and safe production of bio-products such as enzymes. The ability to withstand with harsh conditions and producing spores makes Bacillus a suitable candidate for surface display technology. In recent years, the spores of such specie are widely used as it is generally regarded as safe to use. Advances in synthetic biology have enabled the reprogramming of biofilms to improve their functions and enhance the production of value-added products. Globally, there is increased interest in the production of engineered biosensors, biocatalysts, and biomaterials. The elastic modulus and gel properties of B. subtilis biofilms have been utilized to develop living materials. This review outlines the formation of B. subtilis biofilms and spores. Biotechnological engineering processes and their increasing application in bioremediation and biocatalysis, as well as the future directions of B. subtilis biofilm engineering, are discussed. Furthermore, the ability of B. subtilis biofilms and spores to fabricate functional living materials with self-regenerating, self-regulating and environmentally responsive characteristics has been summarized. This review aims to resume advances in biological engineering of B. subtilis biofilms and spores and their applications.

Depolymerization and conversion of lignin to value-added bioproducts by microbial and enzymatic catalysis

Lignin, the most abundant renewable aromatic compound in nature, is an excellent feedstock for value-added bioproducts manufacturing; while the intrinsic heterogeneity and recalcitrance of which hindered the efficient lignin biorefinery and utilization. Compared with chemical processing, bioprocessing with microbial and enzymatic catalysis is a clean and efficient method for lignin depolymerization and conversion. Generally, lignin bioprocessing involves lignin decomposition to lignin-based aromatics via extracellular microbial enzymes and further converted to value-added bioproducts through microbial metabolism. In the review, the most recent advances in degradation and conversion of lignin to value-added bioproducts catalyzed by microbes and enzymes were summarized. The lignin-degrading microorganisms of white-rot fungi, brown-rot fungi, soft-rot fungi, and bacteria under aerobic and anaerobic conditions were comparatively analyzed. The catalytic metabolism of the microbial lignin-degrading enzymes of laccase, lignin peroxidase, manganese peroxidase, biphenyl bond cleavage enzyme, versatile peroxidase, and β-etherize was discussed. The microbial metabolic process of H-lignin, G-lignin, S-lignin based derivatives, protocatechuic acid, and catechol was reviewed. Lignin was depolymerized to lignin-derived aromatic compounds by the secreted enzymes of fungi and bacteria, and the aromatics were converted to value-added compounds through microbial catalysis and metabolic engineering. The review also proposes new insights for future work to overcome the recalcitrance of lignin and convert it to value-added bioproducts by microbial and enzymatic catalysis.

2G waste lignin to fuel and high value-added chemicals: Approaches, challenges and future outlook for sustainable development

Lignin is produced as a byproduct in cellulosic biorefinery as well in pulp and paper industries and has the potential for the synthesis of a variety of phenolics chemicals, biodegradable polymers, and high value-added chemicals surrogate to conventional petro-based fuels. Therefore, in this critical review, we emphasize the possible scenario for lignin isolation, transformation into value addition chemicals/materials for the economic viability of current biorefineries. Additionally, this review covers the chemical structure of lignocellulosic biomass/lignin, worldwide availability of lignin and describe various thermochemical (homogeneous/heterogeneous base/acid-catalyzed depolymerization, oxidative, hydrogenolysis etc.) and biotechnological developments for the production of bio-based low molecular weight phenolics, i.e. polyhydroxyalkanoates, vanillin, adipic acid, lipids etc. Besides, some functional chemicals applications, lignin-formaldehyde ion exchange resin, electrochemical and production of few targeted chemicals are also elaborated. Finally, we examine the challenges, opportunities and prospects way forward related to lignin valorization.

Feeding strategies to optimize vanillin production by Amycolatopsis sp. ATCC 39116

The growing consumer demand for natural products led to an increasing interest in vanillin production by biotechnological routes. In this work, the biotechnological vanillin production by Amycolatopsis sp. ATCC 39116 is studied using ferulic acid as precursor, aiming to achieve maximized vanillin productivities. During biotech-vanillin production, the effects of glucose, vanillin and ferulic acid concentrations in the broth proved to be relevant for vanillin productivity. Concerning glucose, its presence in the broth during the production phase avoids vanillin conversion to vanillic acid and, consequently, increases vanillin production. To avoid the accumulation of vanillin up to a toxic concentration level, a multiple-pulse-feeding strategy is implemented, with intercalated vanillin removal from the broth and biomass recovery. This strategy turned out fruitful, leading to 0.46 g L^-1 h^-1 volumetric productivity of vanillin of and a production yield of 0.69 g_vanillin g_{ferulic acid}^-1, which are among the highest values reported in the literature for non-modified bacteria.

Recent advancement in lignin biorefinery: With special focus on enzymatic degradation and valorization

With the intensive development of lignocellulosic biorefineries to produce fuels and chemicals from biomass-derived carbohydrates, lignin was generated at a large quantity every year. Therefore, lignin has received increasing attention as an abundant aromatics resource in terms of research and development efforts for value-added chemicals production. In this review, studies about lignin degradation especially the crucial enzymes involved and the reaction mechanism were substantially discussed, which provided the molecular basis of lignin biodegradation. Then, the latest improvements in lignin valorization by biological methods were summarized and case studies about value-added compounds from lignin were introduced. Afterwards, challenges, opportunities and prospects regarding biorefinery of lignin were presented.

Lignin depolymerization and utilization by bacteria

Lignin compound wastes are generated as a result of agricultural and industrial practices. Microorganism-mediated bio-catalytic processes can depolymerize and utilize lignin eco-friendly. Although fungi have been studied since several decades for their ability to depolymerize lignin, strict growth conditions of fungus limit it's industrial application. Compared with fungi, bacteria can tolerate wider pH, temperature, oxygen ranges and are easy to manipulate. Several studies have focused on bacteria involved in the process of lignin depolymerization and utilization. Pseudomonas have been used for paper mill wastewater treatment while Rhodococcus are widely reported to accumulate lipid. In this review, the recent studies on bacterial utilization in paper wastewater treatment, lignin conversion to biofuels, bioplastic, biofertilizers and other value-added chemicals are summarized. As bacteria possess remarkable advantages in industrial production, they may play a promising role in the future commercial lignin utilization.