Bioconversion of ferulic acid into aroma compounds by newly isolated yeast strains of the Latin American biodiversity

Microbial cell factories for bioconversion of lignin to vanillin - Challenges and opportunities: A review

The bioconversion of lignin into vanillin via microbial cell factories offers a promising and sustainable route for producing high-value aromatic compounds from the abundant and underutilized byproducts of plant biomass. This review comprehensively explores the synthesis, structural characteristics, and diverse industrial applications of lignin, while addressing the inherent challenges posed by its complex structure in bioconversion processes. It examines the potential of microbial cell factories for lignin degradation, emphasizing the latest advancements in genetic engineering and metabolic optimization strategies that enhance microbial efficiency in lignin degradation and vanillin biosynthesis. It further assesses the economic feasibility of lignin-to-vanillin conversion by discussing key factors influencing cost-effectiveness and scalability, highlighting the transformative potential for producing high-value aromatic compounds in an environmentally sustainable manner. The review also highlights ongoing research efforts to develop robust microbial strains and optimize metabolic pathways for improved vanillin yield. By integrating multidisciplinary approaches, this review highlights the transformative potential of microbial cell factories to valorize lignin, offering a sustainable pathway for the production of vanillin and related aromatic compounds.

Hydroxycinnamic Acid Extraction from Multiple Lignocellulosic Sources: Correlations with Substrate Composition and Taxonomy for Flavoring and Antioxidant Applications

The extraction of hydroxycinnamic acids (HCADs) is a strategy for lignocellulosic biomass valorization due to their high value-added nature and the possibility of application as flavoring and antioxidants. This study proposes correlations between the composition and taxonomy of 28 globally available agro-industrial feedstocks with the production of HCADs using chemometric tools. Principal component analysis indicated strong correlations between ferulic acid release and hemicellulose type and content, especially in grass biomasses. Conversely, p-coumaric acid release was mainly correlated with cellulose content across diverse taxonomic origins. Among the evaluated agro-industrial feedstocks, corn-based biomasses were identified as prime sources of ferulic acid after mild alkaline treatment, releasing up to 10.5 g kg-1 and producing hydrolysates with an antioxidant capacity up to 3.3 mmol Trolox equivalents g-1. Notably, sugar cane bagasse was the best source of p-coumaric acid, yielding 4.8 g kg-1. Corn hydrolysates were successfully converted into 4-vinylguaiacol using a genetically modified Saccharomyces cerevisiae strain, achieving high yields of 0.75 g L-1. This work enhances our understanding of HCAD sources and biomass valorization strategies, demonstrating potential applications in the food and cosmetics sectors.

Mycobiota of Mexican Maize Landraces with Auxin-Producing Yeasts That Improve Plant Growth and Root Development

Compared to agrochemicals, bioinoculants based on plant microbiomes are a sustainable option for increasing crop yields and soil fertility. From the Mexican maize landrace "Raza cónico" (red and blue varieties), we identified yeasts and evaluated in vitro their ability to promote plant growth. Auxin production was detected from yeast isolates and confirmed using Arabidopsis thaliana plants. Inoculation tests were performed on maize, and morphological parameters were measured. Eighty-seven yeast strains were obtained (50 from blue corn and 37 from red corn). These were associated with three families of Ascomycota (Dothideaceae, Debaryomycetaceae, and Metschnikowiaceae) and five families of Basidiomycota (Sporidiobolaceae, Filobasidiaceae, Piskurozymaceae, Tremellaceae, and Rhynchogastremataceae), and, in turn, distributed in 10 genera (Clavispora, Rhodotorula, Papiliotrema, Candida, Suhomyces, Soliccocozyma, Saitozyma Holtermaniella, Naganishia, and Aeurobasidium). We identified strains that solubilized phosphate and produced siderophores, proteases, pectinases, and cellulases but did not produce amylases. Solicoccozyma sp. RY31, C. lusitaniae Y11, R. glutinis Y23, and Naganishia sp. Y52 produced auxins from L-Trp (11.9-52 µg/mL) and root exudates (1.3-22.5 µg/mL). Furthermore, they stimulated the root development of A. thaliana. Inoculation of auxin-producing yeasts caused a 1.5-fold increase in maize plant height, fresh weight, and root length compared to uninoculated controls. Overall, maize landraces harbor plant growth-promoting yeasts and have the potential for use as agricultural biofertilizers.

Unravel the regulatory mechanism of Yrr1p phosphorylation in response to vanillin stress in Saccharomyces cerevisiae

Improving the resistance of Saccharomyces cerevisiae to vanillin, derived from lignin, will benefit the design of robust cell factories for lignocellulosic biorefining. The transcription factor Yrr1p mediates S. cerevisiae resistance to various compounds. In this study, eleven predicted phosphorylation sites were mutated, among which 4 mutants of Yrr1p, Y134A/E and T185A/E could improve vanillin resistance. Both dephosphorylated and phosphorylated mutations at Yrr1p 134 and 185 gathered in the nucleus regardless of the presence or absence of vanillin. However, the phosphorylated mutant Yrr1p inhibited target gene expression, while dephosphorylated mutants promoted expression. Transcriptomic analysis showed that the dephosphorylated Yrr1p T185 mutant, under vanillin stress, upregulated ribosome biogenesis and rRNA processing. These results demonstrate the mechanism by which Yrr1p phosphorylation regulates the expression of target genes. The identification of key phosphorylation sites in Yrr1p offers novel targets for the rational construction of Yrr1p mutants to improve resistance to other compounds.

Capture Hi-C reveals the influence on dynamic three-dimensional chromosome organization perturbed by genetic variation or vanillin stress in Saccharomyces cerevisiae

Studying the mechanisms of resistance to vanillin in microorganisms, which is derived from lignin and blocks a major pathway of DNA double-strand break repair in yeast, will benefit the design of robust cell factories that produce biofuels and chemicals using lignocellulosic materials. A high vanillin-tolerant Saccharomyces cerevisiae strain EMV-8 carrying site mutations compared to its parent strain NAN-27 was selected for the analyses. The dynamics of the chromatin structure of eukaryotic cells play a critical role in transcription and the regulation of gene expression and thus the phenotype. Consequently, Hi-C and transcriptome analyses were conducted in EMV-8 and NAN-27 in the log phase with or without vanillin stress to determine the effects of mutations and vanillin disturbance on the dynamics of three-dimensional chromosome organization and the influence of the organization on the transcriptome. The outcomes indicated that the chromosome interaction pattern disturbed by vanillin stress or genetic mutations in the log phase was similar to that in mouse cells. The short chromosomes contact the short chromosomes, and the long chromosomes contact the long chromosomes. In response to vanillin stress, the boundaries of the topologically associating domain (TAD) in the vanillin-tolerant strain EMV-8 were more stable than those in its parent strain NAN-27. The motifs of SFL1, STB3, and NHP6A/B were enriched at TAD boundaries in both EMV-8 and NAN-27 with or without vanillin, indicating that these four genes were probably related to TAD formation. The Indel mutation of YRR1, whose absence was confirmed to benefit vanillin tolerance in EMV-8, caused two new interaction sites that contained three genes, WTM2, PUP1, and ALE1, whose overexpression did not affect vanillin resistance in yeast. Overall, our results revealed that in the log phase, genetic mutations and vanillin disturbance have a negligible effect on three-dimensional chromosome organization, and the reformation or disappearance of TAD boundaries did not show an association with gene expression, which provides an example for studying yeast chromatin structure during stress tolerance using Hi-C technology.

Production of flavor compounds from rice bran by yeasts metabolisms of Kluyveromyces marxianus and Debaryomyces hansenii

The aim of this study was to evaluate the biosynthesis of flavor compounds from rice bran by fermentation facilitated by Kluyveromyces marxianus and Debaryomyces hansenii. The growth of both yeasts was assessed by specific growth rates and doubling time. The biosynthesis of flavor compounds was evaluated by gas chromatography-olfactometry (GC-O), gas chromatography-mass spectrometry (GC-MS), and Spectrum™ sensory analysis. The specific growth rate (µ) and doubling time (t_d) of K. marxianus was calculated as 0.16/h and 4.21h, respectively, whereas that of D. hansenii was determined as 0.13/h and 5.33h, respectively. K. marxianus and D. hansenii produced significant levels of higher alcohols and acetate esters from rice bran. Results showed that K. marxianus can produce 827.27 µg/kg of isoamyl alcohol, 169.77 µg/kg of phenyl ethyl alcohol, and 216.08 µg/kg of phenyl ethyl acetate after 24-h batch fermentation. A significant amount of isovaleric acid was also synthesized by K. marxianus (4013 µg/kg) after the batch fermentation of 96 h. 415.64 µg/kg of isoamyl alcohol and 135.77 µg/kg of phenyl ethyl acetate was determined in rice bran fermented by D. hansenii after 24-h fermentation. Fermented cereals and rose were the characteristic flavor descriptors of the fermented rice bran samples. Rose flavor in fermented rice bran samples was found to be associated with phenyl ethyl alcohol, phenyl ethyl acetate, isoamyl acetate, and guaiacol. Thus, the findings of this study demonstrate that the valorization of rice bran can be achieved with the production of natural flavor compounds by yeast metabolism.

Low-Temperature Biodegradation of Lignin-Derived Aromatic Model Monomers by the Cold-Adapted Yeast Rhodosporidiobolus colostri Isolated from Alpine Forest Soil

The contribution of cold-adapted yeasts to the emerging field of lignin biovalorization has not yet been studied. The red-pigmented basidiomycetous yeast strain Rhodosporidiobolus colostri DBVPG 10655 was examined for its potential to degrade five selected lignin-derived aromatic monomers (syringic acid, p-coumaric acid, 4-hydroxybenzoic acid, ferulic acid, and vanillic acid). The strain utilized p-coumaric acid, 4-hydroxybenzoic acid, and ferulic acid not only as the sole carbon source; full biodegradation occurred also in mixtures of multiple monomers. Vanillic acid was not utilized as the sole carbon source, but was degraded in the presence of p-coumaric acid, 4-hydroxybenzoic acid, and ferulic acid. Syringic acid was utilized neither as the sole carbon source nor in mixtures of compounds. Biodegradation of lignin-derived aromatic monomers was detected over a broad temperature range (1–25 °C), which is of ecological significance and of biotechnological relevance.

Streptomyces tunisiensis DSM 42037 mediated bioconversion of ferulic acid released from barley bran

Streptomyces tunisiensis DSM 42037 exhibited growth capacity on a minimum medium containing 1% barley bran. This peculiar strain released 83.5% of total ferulic acid present in barley bran after 5 days of incubation and the highest amount of released ferulic acid (19 mg/L) was observed on the 3rd day of incubation. The concentrated supernatant of S. tunisiensis also released ferulic acid from the parietal arabinoxylan complex of barley bran. This strain was able to convert the free ferulic acid into 4-vinyl guaiacol (14 mg/L) and acetovanillone (12 mg/L) at molar yield of 97% and 83% respectively. The biotransformation products were successively purified by preparative thin layer and silica gel column chromatography followed by HPLC and identified by ¹H nuclear magnetic resonance. Streptomyces tunisiensis DSM 42037 could have potential applications in the food, pharmaceutical and cosmetic industries thanks to its ability in biotransforming ferulic acid into 4-vinyl guaiacol and acetovanillone.