Terpenoids
constitute a structurally diverse group of natural products
with wide applications in the pharmaceutical, nutritional, flavor
and fragrance industries. Fungi are known to produce a large variety
of terpenoids, yet fungal terpene synthases remain largely unexploited.
Here, we report the sesquiterpene network and gene clusters of the
black poplar mushroom Agrocybe aegerita. Among 11
putative sesquiterpene synthases (STSs) identified in its genome,
nine are functional, including two novel synthases producing viridiflorol
and viridiflorene. On this basis, an additional 1133 STS homologues
from higher fungi have been curated and used for a sequence similarity
network to probe isofunctional STS groups. With the focus on two STS
groups, one producing viridiflorene/viridiflorol and one Δ6-protoilludene, the isofunctionality was probed and verified.
Three new Δ6-protoilludene synthases and two new
viridflorene/viridiflorol synthases from five different fungi were
correctly predicted. The study herein serves as a fundamental predictive
framework for the discovery of fungal STSs and biosynthesis of novel
terpenoids. Furthermore, it becomes clear that fungal STS function
differs between the phyla Ascomycota and Basidiomycota with the latter
phylum being more dominant in the overall number and variability.
This study aims to encourage the scientific community to further work
on fungal STS and the products, biological functions, and potential
applications of this vast source of natural products.
The white-rot fungus Pleurotus sapidus (PSA) biosynthesizes the bicyclic monoterpenoids 3,6-dimethyl-2,3,3a,4,5,7a-hexahydrobenzofuran (dill ether) (1) and 3,6-dimethyl-3a,4,5,7a-tetrahydro-1-benzofuran-2(3H)-one (wine lactone) (2). Submerged cultures grown in different media were analyzed by gas chromatography−mass spectrometry. The stereochemistry of the formed isomers was elucidated by comparing their retention indices to those of reference compounds by enantioselective multidimensional gas chromatography. The basidiomycete produced the rare (3R,3aR,7aS) and (3S,3aR,7aS) stereoisomers of dill ether and wine lactone. Kinetic analyses of the volatilome and bioprocess parameters revealed that the biosynthesis of the bicyclic monoterpenoids correlated with the availability of the primary carbon source glucose. Spiking the media with 13 C-labeled glucose demonstrated that the compounds were produced de novo. Supplementation studies i.a. with isotopically labeled substrates further identified limonene and p-menth-1-en-9-ol as intermediate compounds in the fungal pathways. PSA was able to biotransform all enantiomeric forms of the latter compounds to the respective isomers of dill ether and wine lactone.
In order to study the impact of different gas compositions on the bactericidal efficiency of cold atmospheric plasma jets, a device with a controlled atmosphere is built. Various mixtures of argon and helium with air are studied regarding their sterilizing effect on Escherichia coli in solution. Bacteria reduction rates react fundamentally different on addition of air in both gases. In case of helium, a distinct maximum for small admixtures is observed.
Several diagnostic techniques were applied to the plasma. Stronger formation of peroxynitrous acid due to higher concentrations of hydrogen peroxide and nitrite is found to be responsible for the observed trends and differences. The presented findings are important for the development of efficient treatment devices.
A cereal-based beverage was developed by fermentation of wort with the basidiomycete Trametes versicolor. The beverage possessed a fruity, fresh, and slightly floral aroma. The volatiles of the beverage were isolated by liquid-liquid extraction (LLE) and additionally by headspace solid phase microextraction (HS-SPME). The aroma compounds were analyzed by a gas chromatography system equipped with a tandem mass spectrometer and an olfactory detection port (GC-MS/MS-O) followed by aroma (extract) dilution analysis. Thirty-four different odor impressions were perceived, and 27 corresponding compounds were identified. Fifteen key odorants with flavor dilution (FD) factors ranging from 8 to 128 were quantitated, and their respective odor activity values (OAVs) were calculated. Six key odorants were synthesized de novo by T. versicolor. Furthermore, quantitative changes during the fermentation process were analyzed. To prepare for the market introduction of the beverage, a comprehensive safety assessment was performed.
Fermentation
broths of Ashbya gossypii from the
industrial production of riboflavin emit an intense floral,
fruity, and nutty smell. Typical Ehrlich pathway products, such as
2-phenylethan-1-ol and 2-/3-methylbutan-1-ol, were detected in large
amounts as well as some intensely smelling saturated and unsaturated
lactones, e.g., γ-decalactone and γ-(Z)-dodec-6-enlactone. An aroma extract dilution analysis identified
2-phenylethan-1-ol and γ-(Z)-dodec-6-enlactone
as the main contributors to the overall aroma, with flavor dilution
factors of 32 768. The position of the double bonds of unsaturated
lactones was determined by the Paternò–Büchi
reaction, and reference compounds that were not available commercially
were synthesized to elucidate the structures of the uncommon lactones.
The absolute configuration and enantiomeric excess values of the lactones
were determined by converting the lactones to their corresponding
Mosher’s esters. In addition, the odor impressions and odor
thresholds in air were determined.
Lipid extracts of the fungus Flammulina velutipes were found to contain various
scarce fatty acids including dodec-11-enoic
acid and di- and tri-unsaturated C16 isomers. A biotechnological
approach using a heterologously expressed carboxylic acid reductase
was developed to transform the fatty acids into the respective aldehydes,
yielding inter alia dodec-11-enal. Supplementation
studies gave insights into the fungal biosynthesis of this rarely
occurring acid and suggested a terminal desaturation of lauric acid
being responsible for its formation. A systematic structure–odor
relationship assessment of terminally unsaturated aldehydes (C7–C13) revealed odor thresholds in the range
of 0.24–22 μg/L in aqueous solution and 0.039–29
ng/L in air. In both cases, non-8-enal was identified as the most
potent compound. All aldehydes exhibited green odor qualities. Short-chained
substances were additionally associated with grassy, melon-, and cucumber-like
notes, while longer-chained homologs smelled soapy and coriander leaf-like
with partly herbaceous nuances. Dodec-11-enal turned out to be of
highly pleasant scent without off-notes.
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