Transformation of alpha-pinene using Picea abies suspension culture

Know When You Are Too Many: Density-Dependent Release of Pheromones During Host Colonisation by the European Spruce Bark Beetle, Ips typographus (L.)

Individuals across various animal species communicate their presence to conspecifics. Especially phytophagous and parasitoid insects with their brood developing on limited resources rely on chemical cues, such as host-marking pheromones, to reduce intraspecific competition. Bark beetles are phytophagous insects with some species being economically and ecologically relevant forest pests. Several of them use the volatile compound verbenone to inhibit attraction and reduce intraspecific competition. However, in the Eurasian spruce bark beetle, Ips typographus (L.), temporal emission patterns did so far not quite support the putative function of verbenone as an indicator of densely colonised host trees. More importantly, it is currently unclear how well verbenone emission is actually related to colonisation density and thus intraspecific competition. Here, we inoculated Norway spruce logs with I. typographus at two defined colonisation densities in the greenhouse and measured the emission of verbenone and its precursors α-pinene and verbenol over time. Verbenone emission was 3-7 times greater from colonised logs compared to decaying logs without beetles during the major part of larval development. Furthermore, our data supports the quantitative hypothesis, that the termination of attack on a tree is mediated by a cessation of the release of verbenol and continuous emission of verbenone. The latter is most likely a passively produced host-marking cue reflecting the actual density of conspecifics since per-beetle emission was unaffected by colonisation density. These findings shed new light on the regulation of bark beetle mass aggregations, which are currently causing previously unseen economic damages in temperate forests.

Potential enzymes involved in beer monoterpenoids transformation: structures, functions and challenges

Monoterpenes are important flavor and fragrance compounds in food. In beer, the monoterpenes mainly come from hops added during boiling process. Biotransformations of monoterpene which occurred during fermentation conferred beer with various kinds of aroma profiles, which can be mainly attributed to the contribution of enzymes in yeast. However, there are few reports on the identification and characterization of these enzymes in yeast. Illustrating the structure and functions of key enzymes related to transformations will broaden their potential applications in beer or other foodstuffs. Monoterpenoids including terpene hydrocarbons (limonene, myrcene, and pinene) and terpene alcohol (linalool, geraniol, nerol, and citronellol) gave the beer flower-like or fruit-like aroma. The biotransformation of monoterpenes and monoterpene alcohols in bacteria and yeast, and potential enzymes related to the transformation of them are reviewed here. Enzymes primarily are dehydrogenases including linalool dehydrogenase/isomerase, geraniol/geranial dehydrogenase, nerol dehydrogenase and citronellol dehydrogenase. Most of them are substrate-specific or substrate-specific after modifications by biotechnology methods, and part of them have been expressed in E. coli, while the purification and catalytic rate is very low. Efforts should be made to acquire abundant enzymes, and to fabricate enzyme-expressing yeast, which can be further applied in beer fermentation system.highlightsMonoterpenoids contributed to the flavor of food, especially beer.Transformation of monoterpenoids occurred during fermentation.Various kinds of enzymes are involved in the transformation of monoterpenoids in bacteria, yeast, etc.Crystal structures of these enzymes have been partially resolved.Few enzymes are further applied in food system to obtain abundant flavor.

Identification of Fungal Limonene-3-Hydroxylase for Biotechnological Menthol Production

More than 30,000 tons of menthol are produced every year as a flavor and fragrance compound or as a medical component. So far, only extraction from plant material and chemical synthesis are possible. An alternative approach for menthol production could be a biotechnological-chemical process with ideally only two conversion steps, starting from (+)-limonene, which is a side product of the citrus processing industry. The first step requires a limonene-3-hydroxylase (L3H) activity that specifically catalyzes hydroxylation of limonene at carbon atom 3. Several protein engineering strategies have already attempted to create limonene-3-hydroxylases from bacterial cytochrome P450 monooxygenases (CYPs, or P450s), which can be efficiently expressed in bacterial hosts. However, their regiospecificity is rather low compared to that of the highly selective L3H enzymes from the biosynthetic pathway for menthol in Mentha species. The only naturally occurring limonene-3-hydroxylase activity identified in microorganisms so far was reported for a strain of the black yeast-like fungus Hormonema sp. in South Africa. We have discovered additional fungi that can catalyze the intended reaction and identified potential CYP-encoding genes within the genome sequence of one of the strains. Using heterologous gene expression and biotransformation experiments in yeasts, we were able to identify limonene-3-hydroxylases from Aureobasidium pullulans and Hormonema carpetanum Further characterization of the A. pullulans enzyme demonstrated its high stereospecificity and regioselectivity, its potential for limonene-based menthol production, and its additional ability to convert α- and β-pinene to verbenol and pinocarveol, respectively.IMPORTANCE (-)-Menthol is an important flavor and fragrance compound and furthermore has medicinal uses. To realize a two-step synthesis starting from renewable (+)-limonene, a regioselective limonene-3-hydroxylase enzyme is necessary. We identified enzymes from two different fungi which catalyze this hydroxylation reaction and represent an important module for the development of a biotechnological process for (-)-menthol production from renewable (+)-limonene.

Cascade Biocatalysis Designed for the Allylic Oxidation of α-Pinene

A biocatalytic cascade system using a cocktail of oxidoreductase enzymes (2-1B peroxidase and M120 laccase) was designed for the allylic oxidation of (+)-α-pinene into value-added products (e.g., verbenol and verbenone). The oxidative transformation involved a two-step process as follows: (+)-α-pinene was (i) oxidized on the allylic position with H2O2 mainly assisted by 2-1B peroxidase leading to verbenol as the principal reaction product, and (ii) directed to verbenone in the presence of M120 laccase responsible for further oxidation of verbenol to verbenone. The reaction environment was ensured by the acetate buffer (0.1 M, pH = 5). Optimum values for the experimental parameters (e.g., concentration of 2-1B peroxidase, M120 laccase, and H2O2) were set up. The biocatalytic cascade process was monitored for 24 h in order to evaluate the process pathway. Maximum performance under optimum conditions was reached after 5 h incubation time (e.g., 80% (+)-α-pinene conversion and 70% yield in verbenol). Therefore, the developed biocatalytic cascade system offered promising perspectives for (+)-α-pinene valorization.

Biotransformation of α- and β-pinene into flavor compounds

Products that bear the label "natural" have gained more attention in the marketplace. In this approach, the production of aroma compounds through biotransformation or bioconversion has been receiving more incentives in economic and research fields. Among the substrates used in these processes, terpenes can be highlighted for their versatility and low cost; some examples are limonene, α-pinene, and β-pinene. This work focused on the biotransformation of the two bicyclic monoterpenes, α-pinene and β-pinene; the use of different biocatalysts; the products obtained; and the conditions employed in the process.

Synthesis of ε-Viniferin Glycosides by Glucosyltransferase from Phytolacca americana and their Inhibitory Activity on Histamine Release from Rat Peritoneal Mast Cells

Glycosylation of (+)-ε-viniferin was investigated using glucosyltransferase from Phytolacca americana ( PaGT3) as a biocatalyst. (+)-ε-Viniferin was converted by PaGT3 into its 4b- and 13b-β-D-glucosides, the inhibitory activities on histamine release from rat peritoneal mast cells of which were higher than that of (+)-ε-viniferin.

Synthesis of Resveratrol Glycosides by Plant Glucosyltransferase and Cyclodextrin Glucanotransferase and Their Neuroprotective Activity

Resveratrol was converted by glucosyltransferase from Phytolacca americana into its 3- and 4′- O-β-D-glucosides. On the other hand, further glycosylation of resveratrol 4′- O-β-D-glucoside by cyclodextrin glucanotransferase gave the 4′- O-β-maltoside, 4′- O-β-maltotrioside, 4′- O-β-maltotetraoside, and 4′- O-β-maltopentaoside of resveratrol. The six resveratrol glycosides synthesized here showed higher phosphodiesterase inhibitory activity than resveratrol.

Regioselective Glycosylation of 3-, 5-, 6-, and 7-Hydroxyflavones by Cultured Plant Cells

Regioselective glycosylation of 3-, 5-, 6-, and 7-hydroxyflavones was investigated using cultured plant cells of Eucalyptus perriniana and Phytolacca americana as biocatalysts. 3- and 7-Hydroxyflavones were practically glycosylated into the corresponding β-D-glucosides by E. perriniana and P. americana.

Glycosylation of Quercetin with Cultured Plant Cells and Cyclodextrin Glucanotransferase

Quercetin was glucosylated by cultured plant cells of Ipomoea batatas to its 3- and 7- O-β-D-glucosides, and 3,7- O-β-D-diglucoside. On the other hand, further glycosylation of quercetin 3-O-β-D-glucoside by cyclodextrin glucanotransferase gave the 3-O-β-maltoside, 3-O-β-maltotrioside, and 3-O-β-maltotetraosides of quercetin.

Glycosylation of Artepillin C with Cultured Plant Cells of Phytolacca americana

Biotransformation of artepillin C was investigated using cultured plant cells as biocatalysts. Artepillin C was converted into its 4- and 9-β-D-glucosides, and 4,9-β-D-diglucoside by cultured cells of Phytolacca americana. In contrast, cultured Ipomoea batatas cells glucosylated artepillin C to only its 4- and 9-β-D-glucosides.

Glucosylation of Taxifolin with Cultured Plant Cells

Cultured plant cells of Eucalyptus perriniana glucosylated taxifolin to its 3′- and 7- O-β-D-glucosides and 3′,7- O-β-D-diglucoside. On the other hand taxifolin was converted into 3′- and 7- O-β-D-glucosides by cultured cells of Nicotiana tabacum and Catharanthus roseus.

Regioselective Hydroxylation and Glucosylation of α- and β-Pinenes with Cultured Cells of Eucalyptus perriniana

Cultured plant cells of Eucalyptus perriniana regioselectively hydroxylated (+)- and (-)-α-pinenes to the corresponding (+)- and (-)-verbenols. In addition, (+)-and (-)-verbenols were converted into mono-β-D-glucosides. On the other hand, (+)- and (-)-β-pinenes were transformed into (+)- and (-)-pinocarveol 3- O-β-D-glucosides via (+)- and (-)-pinocarveols.

Functional identification and differential expression of 1-deoxy-D-xylulose 5-phosphate synthase in induced terpenoid resin formation of Norway spruce (Picea abies)

Conifers produce terpenoid-based oleoresins as constitutive and inducible defenses against herbivores and pathogens. Much information is available about the genes and enzymes of the late steps of oleoresin terpenoid biosynthesis in conifers, but almost nothing is known about the early steps which proceed via the methylerythritol phosphate (MEP) pathway. Here we report the cDNA cloning and functional identification of three Norway spruce (Picea abies) genes encoding 1-deoxy-D-xylulose 5-phosphate synthase (DXS), which catalyzes the first step of the MEP pathway, and their differential expression in the stems of young saplings. Among them are representatives of both types of plant DXS genes. A single type I DXS gene is constitutively expressed in bark tissue and not affected by wounding or fungal application. In contrast, two distinct type II DXS genes, PaDXS2A and PaDXS2B, showed increased transcript abundance after these treatments as did two other genes of the MEP pathway tested, 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR) and 4-hydroxyl 3-methylbutenyl diphosphate reductase (HDR). We also measured gene expression in a Norway spruce cell suspension culture system that, like intact trees, accumulates monoterpenes after treatment with methyl jasmonate. These cell cultures were characterized by an up-regulation of monoterpene synthase gene transcripts and enzyme activity after elicitor treatment, as well as induced formation of octadecanoids, including jasmonic acid and 12-oxophytodienoic acid. Among the Type II DXS genes in cell cultures, PaDXS2A was induced by treatment with chitosan, methyl salicylate, and Ceratocystis polonica (a bark beetle-associated, blue-staining fungal pathogen of Norway spruce). However, PaDXS2B was induced by treatment with methyl jasmonate and chitosan, but was not affected by methyl salicylate or C. polonica. Our results suggest distinct functions of the three DXS genes in primary and defensive terpenoid metabolism in Norway spruce.

Biotransformation of a Monoterpene Mixture by in vitro Cultures of Selected Conifer Species

Biotransformation of monoterpenes is a mild and promising method for the production of stereospecific and regiospecific organic compounds. It is advantageous, especially for the preparation of substances with complicated structures and for those that need to be classed as “natural products“. Our study has focused on the biotransformation of a monoterpenic mixture, turpentine, by Picea abies and Taxus baccata suspension cultures. We identified the biotransformation products and compared the metabolite compositions of the tissue cultures. The major biotransformation products of turpentine were trans-pinocarveol, trans-verbenol, verbenone, myrtenol, α-terpineol and trans-sobrerol, which correspond with the products of biotransformation of the individual monoterpenes, α-pinene and β-pinene, by P. abies suspension culture.

Transformation of terpenes using a Picea abies suspension culture

When subjected to a Picea abies suspension cell culture, beta-pinene, either one of the pure enantiomers or the racemate, was transformed mainly to trans-pinocarveol along with the minor products myrtenol, alpha-terpineol, pinocarvone, myrtenal and cis-pinocarveol. The absolute configuration of the major products corresponded to that of the starting beta-pinene enantiomer. Some of the primary transformation products, i.e. (1S)-cis- and (1S)-trans-pinocarveol, (1R)-myrtenol and (4S)-alpha-terpineol, were also tested as substrates of the P. abies suspension culture. They reacted more slowly than beta-pinene but, except for (4S)-alpha-terpineol, they were all transformed. Thus, (1R)-myrtenol was converted into both (1R)-myrtenal and (1R)-myrtanol, whereas (1S)-trans-pinocarveol was converted into (1S)-pinocarvone. (4R)-Limonene was slowly transformed by the suspension culture into limonene-(1,2)-epoxide as the major product, with carveol, perillyl alcohol and 1,8-cineole as minor products. Autoxidation of terpenes in cell-free nutrient medium was investigated in detail. Alpha-pinene and beta-pinene were both autoxidized to a certain extent, while limonene remained unaffected. The rate of the autoxidation was more than one order of magnitude slower than that of the biotransformation. Moreover, different products were formed by autoxidation than by biotransformation.