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The gut microbiota plays a central role in human health by enzymatically degrading dietary fiber and concomitantly excreting short chain fatty acids that are associated with manifold health benefits. The polysaccharide xylan is abundant in dietary fiber but noncarbohydrate decorations hinder efficient cleavage by glycoside hydrolases (GHs) and need to be addressed by carbohydrate esterases (CEs). Enzymes from carbohydrate esterase families 1 and 6 (CE1 and 6) perform key roles in xylan degradation by removing feruloyl and acetate decorations, yet little is known about these enzyme families especially with regard to their diversity in activity. Bacteroidetes bacteria are dominant members of the microbiota and often encode their carbohydrate-active enzymes in multigene polysaccharide utilization loci (PULs). Here we present the characterization of three CEs found in a PUL encoded by the gut Bacteroidete Dysgonomonas mossii. We demonstrate that the CEs are functionally distinct, with one highly efficient CE6 acetyl esterase and two CE1 enzymes with feruloyl esterase activities. One multidomain CE1 enzyme contains two CE1 domains: an N-terminal domain feruloyl esterase, and a C-terminal domain with minimal activity on model substrates. We present the structure of the C-terminal CE1 domain with the carbohydrate-binding module that bridges the two CE1 domains, as well as a complex of the same protein fragment with methyl ferulate. The investment of D. mossii in producing multiple CEs suggests that improved accessibility of xylan for GHs and cleavage of covalent polysaccharide-polysaccharide and lignin-polysaccharide bonds are important enzyme activities in the gut environment.

Pseudomonas putida KT2440 is a promising bacterial chassis for the conversion of lignin-derived aromatic compound mixtures to biofuels and bioproducts. Despite the inherent robustness of this strain, further improvements to aromatic catabolism and toxicity tolerance of P. putida will be required to achieve industrial relevance. Here, tolerance adaptive laboratory evolution (TALE) was employed with increasing concentrations of the hydroxycinnamic acids p-coumaric acid (pCA) and ferulic acid (FA) individually and in combination (pCA ​+ ​FA). The TALE experiments led to evolved P. putida strains with increased tolerance to the targeted acids as compared to wild type. Specifically, a 37 ​h decrease in lag phase in 20 ​g/L pCA and a 2.4-fold increase in growth rate in 30 ​g/L FA was observed. Whole genome sequencing of intermediate and endpoint evolved P. putida populations revealed several expected and non-intuitive genetic targets underlying these aromatic catabolic and toxicity tolerance enhancements. PP_3350 and ttgB were among the most frequently mutated genes, and the beneficial contributions of these mutations were verified via gene knockouts. Deletion of PP_3350, encoding a hypothetical protein, recapitulated improved toxicity tolerance to high concentrations of pCA, but not an improved growth rate in high concentrations of FA. Deletion of ttgB, part of the TtgABC efflux pump, severely inhibited growth in pCA ​+ ​FA TALE-derived strains but did not affect growth in pCA ​+ ​FA in a wild type background, suggesting epistatic interactions. Genes involved in flagellar movement and transcriptional regulation were often mutated in the TALE experiments on multiple substrates, reinforcing ideas of a minimal and deregulated cell as optimal for domesticated growth. Overall, this work demonstrates increased tolerance towards and growth rate at the expense of hydroxycinnamic acids and presents new targets for improving P. putida for microbial lignin valorization., Graphical abstract Image 1, Highlights • Pseudomonas putida was evolved in increasing hydroxycinnamic acid concentrations. • The lag phase in high p-coumaric acid concentration was reduced. • The growth rate and tolerance to high ferulic acid concentration was increased. • PP_3350 and ttgB contribute to the observed phenotypes.

The outbreak of mysterious pneumonia at the end of 2019 is associated with widespread research interest worldwide. The coronavirus disease-19 (COVID-19) targets multiple organs through inflammatory, immune, and redox mechanisms, and no effective drug for its prophylaxis or treatment has been identified until now. The use of dietary bioactive compounds, such as phenolic compounds (PC), has emerged as a putative nutritional or therapeutic adjunct approach for COVID-19. In the present study, scientific data on the mechanisms underlying the bioactivity of PC and their usefulness in COVID-19 mitigation are reviewed. In addition, antioxidant, antiviral, anti-inflammatory, and immunomodulatory effects of dietary PC are studied. Moreover, the implications of digestion on the putative benefits of dietary PC against COVID-19 are presented by addressing the bioavailability and biotransformation of PC by the gut microbiota. Lastly, safety issues and possible drug interactions of PC and their implications in COVID-19 therapeutics are discussed.

Dietary phenolics may play a protective role in UV-mediated skin pigmentation through their antioxidant and UV-absorbing actions. In this study, we investigated whether genetic silencing of Nrf2, regulating the transcription of antioxidant genes, affected melanogenesis in primary human epidermal melanocytes (HEMn) and B16F10 melanoma cells subjected to UVA (8 J/cm2) exposure. Then, we explored the antimelanogenic actions of phenolics; caffeic acid (CA) and ferulic acid (FA) providing partial UVA protection; quercetin (QU) and rutin (RU) providing strong UVA protection and; avobenzone (AV), an efficient UVA filter, in association with modulation of Nrf2-mediated antioxidant defenses in response to UVA insults in B16F10 cells. Upon oxidative insults, Nrf2 silencing promoted melanogenesis in both HEMn and B16F10 cells irradiated with UVA. Stimulation of melanogenesis by UVA correlated with increased ROS and oxidative DNA damage (8-OHdG), GSH depletion as well as a transient downregulation of Nrf2 nuclear translocation and of Nrf2-ARE signaling in B16F10 cells. All test compounds exerted antimelanogenic effects with respect to their abilities to reverse UVA-mediated oxidative damage as well as downregulation of Nrf2 activity and its target antioxidants (GCLC, GST and NQO1) in B16F10 cells. In conclusion, defective Nrf2 may promote melanogenesis under UVA irradiation through oxidative stress mechanisms. Compounds with antioxidant and/or UVA absorption properties could protect against UVA-induced melanogenesis through indirect regulatory effect on Nrf2-ARE pathway., Graphical abstract fx1, Highlights • Depletion of Nrf2 could stimulate melanogenesis under UVA-mediated oxidative stress. • UVA caused time-course changes of Nrf2 activity and its target antioxidants. • Phenolics could inhibit UVA-induced melanogenesis through modulation of Nrf2 pathway.

Dietary fiber-derived short-chain fatty acids (SCFA) and phenolics produced by the gut microbiome have multiple effects on health. We have tested the hypothesis that long-term exposure to physiological concentrations of SCFA can affect the transport and metabolism of (poly)phenols by the intestinal epithelium using the Caco-2 cell model. Metabolites and conjugates of hesperetin (HT) and ferulic acid (FA), gut-derived from dietary hesperidin and chlorogenic acid, respectively, were quantified by LC-MS with authentic standards following transport across differentiated cell monolayers. Changes in metabolite levels were correlated with effects on mRNA and protein expression of key enzymes and transporters. Propionate and butyrate increased both FA transport and rate of appearance of FA glucuronide apically and basolaterally, linked to an induction of MCT1. Propionate was the only SCFA that augmented the rate of formation of basolateral FA sulfate conjugates, possibly via basolateral transporter up-regulation. In addition, propionate enhanced the formation of HT glucuronide conjugates and increased HT sulfate efflux toward the basolateral compartment. Acetate treatment amplified transepithelial transport of FA in the apical to basolateral direction, associated with lower levels of MCT1 protein expression. Metabolism and transport of both HT and FA were curtailed by the organic acid lactate owing to a reduction of UGT1A1 protein levels. Our data indicate a direct interaction between microbiota-derived metabolites of (poly)phenols and SCFA through modulation of transporters and conjugating enzymes and increase our understanding of how dietary fiber, via the microbiome, may affect and enhance uptake of bioactive molecules.

During the wet separation of starch and gluten, both water extractable pentosans (WEP) and water unextractable solids (WUS) have a negative effect on gluten yield. Gluten properties are also affected: the gluten becomes less extensible. In comparison to the control, addition of WUS or WEP resulted in less gluten with a higher maximum resistance to extension (Rmax) and a smaller extensibility at maximum resistance (E at Rmax). The corresponding glutenin macropolymer (GMP) gel was more elastic, and the specific volume of the GMP particles was larger and their tendency to aggregate was lower. In contrast, the use of xylanase or ferulic acid (FA) resulted in a higher gluten yield and a larger E at Rmax of gluten. Here, the GMP was characterised by a more viscous gel structure, a smaller specific volume of the GMP particles and a larger tendency of GMP particles to aggregate. Correlations between gluten properties (Rmax, E at Rmax) and GMP particle properties ([η], K′) were observed. Based on these observations, we propose a possible explanation for the effect of pentosans on gluten formation and properties. Both a physical effect and a chemical effect are involved. The physical effect is related to viscosity and likely also to depletion attraction between protein particles. The chemical effect is related to a FA-mediated effect and 'controls' the tendency of the particles to aggregate (K′). The contribution of physical and chemical effects leads to a partial agglomeration of GMP particles and shifts the GMP particle size distribution to a higher value. Since GMP particle properties could be directly related to gluten rheological properties, this explains the change in quality observed. © 2004 Elsevier Ltd. All rights reserved.