An Engineered Plant Metabolic Pathway Results in High Yields of Hydroxytyrosol Due to a Modified Whole-Cell Biocatalysis in Bioreactor

Hydroxytyrosol (HT) is a phenolic substance primarily present in olive leaves and olive oil. Numerous studies have shown its advantages for human health, making HT a potentially active natural component with significant added value. Determining strategies for its low-cost manufacturing by metabolic engineering in microbial factories is hence still of interest. The objective of our study was to assess and improve HT production in a one-liter bioreactor utilizing genetically modified Escherichia coli strains that had previously undergone fed-batch testing. Firstly, we compared the induction temperatures in small-scale whole-cell biocatalysis studies and then examined the optimal temperature in a large volume bioreactor. By lowering the induction temperature, we were able to double the yield of HT produced thereby, reaching 82% when utilizing tyrosine or L-DOPA as substrates. Hence, without the need to further modify our original strains, we were able to increase the HT yield.

Hybrid Autofluorescence and Optoacoustic Microscopy for the Label-Free, Early and Rapid Detection of Pathogenic Infections in Vegetative Tissues

Agriculture plays a pivotal role in food security and food security is challenged by pests and pathogens. Due to these challenges, the yields and quality of agricultural production are reduced and, in response, restrictions in the trade of plant products are applied. Governments have collaborated to establish robust phytosanitary measures, promote disease surveillance, and invest in research and development to mitigate the impact on food security. Classic as well as modernized tools for disease diagnosis and pathogen surveillance do exist, but most of these are time-consuming, laborious, or are less sensitive. To that end, we propose the innovative application of a hybrid imaging approach through the combination of confocal fluorescence and optoacoustic imaging microscopy. This has allowed us to non-destructively detect the physiological changes that occur in plant tissues as a result of a pathogen-induced interaction well before visual symptoms occur. When broccoli leaves were artificially infected with Xanthomonas campestris pv. campestris (Xcc), eventually causing an economically important bacterial disease, the induced optical absorption alterations could be detected at very early stages of infection. Therefore, this innovative microscopy approach was positively utilized to detect the disease caused by a plant pathogen, showing that it can also be employed to detect quarantine pathogens such as Xylella fastidiosa.

Vitis vinifera genotyping toolbox to highlight diversity and germplasm identification

The contribution of vine cultivation to human welfare as well as the stimulation of basic social and cultural features of civilization has been great. The wide temporal and regional distribution created a wide array of genetic variants that have been used as propagating material to promote cultivation. Information on the origin and relationships among cultivars is of great interest from a phylogenetics and biotechnology perspective. Fingerprinting and exploration of the complicated genetic background of varieties may contribute to future breeding programs. In this review, we present the most frequently used molecular markers, which have been used on Vitis germplasm. We discuss the scientific progress that led to the new strategies being implemented utilizing state-of-the-art next generation sequencing technologies. Additionally, we attempted to delimit the discussion on the algorithms used in phylogenetic analyses and differentiation of grape varieties. Lastly, the contribution of epigenetics is highlighted to tackle future roadmaps for breeding and exploitation of Vitis germplasm. The latter will remain in the top of the edge for future breeding and cultivation and the molecular tools presented herein, will serve as a reference point in the challenging years to come.

Evolution of Physicochemical Properties and Phenolic Maturity of Vilana, Vidiano, Kotsifali and Mandilari Wine Grape Cultivars (Vitis vinifera L.) during Ripening

Determining the optimum harvest time is a significant factor affecting the quality of the grapes and the wine. Monitoring the evolution of grapes' physicochemical properties and phenolic maturity during ripening could be a valuable tool for determining the optimum harvest time. In this study, the total phenolic content, antioxidant activity, flavonols, flavanols, anthocyanins and resveratrol content were determined during the last weeks of ripening for the white cultivars Vilana and Vidiano, as well as for the red cultivars Kotsifali and Mandilari (Vitis vinifera L.). According to the results, an early harvest for the white cultivars and a late harvest for the red cultivars may increase the total phenolics and trans-resveratrol content in grapes and wine. An early harvest would be desirable to maintain high flavanols content and high levels of antioxidant activity in the grapes' skin and seeds. Conversely, a late harvest for the red cultivars may be desirable to increase the total flavonols and anthocyanin content in grapes and wines.

Resveratrol: A Fair Race Towards Replacing Sulfites in Wines

In recent years, significant efforts to produce healthier wines has led to the replacement or reduction of the addition of sulfites, using alternative substances or techniques. Resveratrol and related biophenols seem to be of great interest, since beyond their protective nature and contrary to sulfites they can positively affect consumer health. These bioactive phytochemicals are naturally produced in grapes as evolutionary acquired mechanisms against pathogens and UV irradiation. However, despite the efforts made so far attempting to develop economic and industrially adopted isolation techniques, available quantities of these biophenols for commercial use are still quite limited. Therefore, such molecules are still not able to meet the needs of industrial use due to their prohibitive marketable cost. In this review we summarize the efforts that have been made to biosynthesize these molecules through alternative, innovative ways. Increasing interest in modern biotechnological approaches has shed light on the exploitation of metabolically engineered microbial factories, instead of plants, to produce molecules of industrial interest. Such approaches, also reviewed here, are expected to lower the cost and appear promising to produce enough surplus to attract further oenological experimentation upon yielding functional wines. This development is expected to attract further industrial attention, continuing the race to partially or totally replace the external addition of sulfites. We also review important physicochemical properties of resveratrol in relation to enriching wines.

Dual pathway for metabolic engineering of Escherichia coli to produce the highly valuable hydroxytyrosol

One of the most abundant phenolic compounds traced in olive tissues is hydroxytyrosol (HT), a molecule that has been attributed with a pile of beneficial effects, well documented by many epidemiological studies and thus adding value to products containing it. Strong antioxidant capacity and protection from cancer are only some of its exceptional features making it ideal as a potential supplement or preservative to be employed in the nutraceutical, agrochemical, cosmeceutical, and food industry. The HT biosynthetic pathway in plants (e.g. olive fruit tissues) is not well apprehended yet. In this contribution we employed a metabolic engineering strategy by constructing a dual pathway introduced in Escherichia coli and proofing its significant functionality leading it to produce HT. Our primary target was to investigate whether such a metabolic engineering approach could benefit the metabolic flow of tyrosine introduced to the conceived dual pathway, leading to the maximalization of the HT productivity. Various gene combinations derived from plants or bacteria were used to form a newly inspired, artificial biosynthetic dual pathway managing to redirect the carbon flow towards the production of HT directly from glucose. Various biosynthetic bottlenecks faced due to feaB gene function, resolved through the overexpression of a functional aldehyde reductase. Currently, we have achieved equimolar concentration of HT to tyrosine as precursor when overproduced straight from glucose, reaching the level of 1.76 mM (270.8 mg/L) analyzed by LC-HRMS. This work realizes the existing bottlenecks of the metabolic engineering process that was dependent on the utilized host strain, growth medium as well as to other factors studied in this work.

Identification and Seasonal Abundance of Auchenorrhyncha With a Focus on Potential Insect Vectors of Xylella fastidiosa in Olive Orchards in Three Regions of Greece

Studies of the species composition, seasonal appearance, and abundance of Auchenorrhyncha in olive crops is of paramount importance to reduce the potential of Xylella fastidiosa to invade new areas. As similar investigations had not previously been conducted in Greece, extensive surveys were undertaken in olive orchards located in three of the most important regions for olive production in central Greece (Fthiotida), south-central Greece (Attica), and southern Greece (Chania). Surveys took place over a 13-mo period, using Malaise traps examined on a monthly basis. Results showed high levels of species richness in the olive orchards, and the Auchenorrhyncha diversity varied among the regions surveyed. Most of the species listed as potential vectors of X. fastidiosa in Europe were found in relatively low numbers. Furthermore, many insects of the Deltocephalinae subfamily were found, whose behavior as vectors should be further studied. The dominant and most frequent species found in the three regions were tested and found not to be associated with transmission of the bacterium. This study may serve as an alert, showing that the most commonly found species differ from those identified in similar studies in Italy, and thus other species should be examined as potential vectors. The results of the present study provide new insights into the seasonal abundance and dynamics of potential vectors of X. fastidosa in several regions of Greece, and also provide information that may prove valuable for the effective containment and eradication of this threat.

Expression of hydroxytyrosol and oleuropein biosynthetic genes are correlated with metabolite accumulation during fruit development in olive, Olea europaea, cv. Koroneiki

Olive tree is one of the most valuable crops cultivated for its oil that is rich in antioxidants. The beneficial effects of oleuropein and hydroxytyrosol (HT), the most abundant and the most powerful antioxidant respectively, as well as tyrosol, HT's precursor molecule, are well studied however their biosynthetic pathways are not yet clarified. The transcriptome analysis of the young olive fruit, cultivar "Koroneiki", revealed transcripts of all the enzymes used to reconstitute the biosynthetic pathway of tyrosol and HT in other organisms. We also identified transcripts of the genes that encode for enzymes involved in the secologanin biosynthesis, oleuropein's precursor molecule. Following the transcriptome analysis, the relative expression of the transcripts was monitored during fruit development and compared to the concentration of the 3 metabolites they synthesize at the same developmental stages. The highest expression levels, accompanied by the maximum concentration of the three metabolites, was found in the young olive fruit. The correlation between the expression profile and the metabolites' concentration indicates that the transcripts were correctly identified and the synthesis of the compounds is regulated at a transcriptional level. Interestingly, HT showed a sudden increment in the final developmental stage of the black mature fruit that is attributed to oleuropein catabolism.

Metabolic engineering of the complete pathway leading to heterologous biosynthesis of various flavonoids and stilbenoids in Saccharomyces cerevisiae

Chemical or biological synthesis of plant secondary metabolites has attracted increasing interest due to their proven or assumed beneficial properties and health promoting effects. Resveratrol, a stilbenoid, naringenin, a flavanone, genistein, an isoflavone, and the flavonols kaempferol and quercetin have been shown to possess high nutritional and agricultural value. Four metabolically engineered yeast strains harboring plasmids with heterologous genes for enzymes involved in the biosynthesis of these compounds from phenylalanine have been constructed. Time course analyses of precursor utilization and end-product accumulation were carried out establishing the production of 0.29-0.31 mg/L of trans-resveratrol, 8.9-15.6 mg/L of naringenin, 0.1-7.7 mg/L of genistein, 0.9-4.6 mg/L of kaempferol and 0.26-0.38 mg/L of quercetin in defined media under optimal growth conditions. The recombinant yeast strains can be used further for the construction of improved flavonoid- and stilbenoid-overproducers.

The role of bulking agent in pile methane and carbon dioxide concentration during wastewater sludge windrow composting

Wastewater sludge and wood chips were used as feedstock for the construction of two piles, Pile I ("PI") and Pile II ("PII"), at a ratio of 1:1 and 1:2 v/v, respectively. Each pile was originally 1.3-m high, 2.0-m wide, and approximately 9.0-m long. A mechanical turner was used to turn the two windrows every 1 to 2 weeks. Three 500-mL-volume glass funnels were inverted and introduced into each pile: one in the core (named, respectively, "PIC" and "PIIC"), one at the top ("PIT" and "PIIT"), and one at the side ("PIS" and "PIIS"). Every 2 to 3 days, gas samples were collected using gas-tight syringes and analyzed in a gas chromatograph determining carbon dioxide (CO2) and methane (CH4) concentrations. An average gas concentration value between turnings was calculated and a two-way analysis of variance test was used to determine the significance of the differences between piles and pile location, followed by a Post Hoc Tukey test. During the thermophilic period, the mean CO2 concentration in PIC was 103 mL/L, 65 mL/L in PIT, and 24 mL/L in PIS, whereas, for PII, these values were 102mL/L, 59 mL/L, and 24 mL/L, respectively. The mean CH4 concentration between turnings in PIC was 9.2 mL/L, 1.9 mL/L in PIT, and 0.9 mL/L in PIS, whereas, for PII, the corresponding values were 6.4 mL/L, 0.4 mL/L, and 0.1 mL/L. For methane, there were no significant differences between these mean values, not only between the same placement in different piles, but also between different placements and different piles. This is probably due to the relatively frequent turnings (10 turnings during a period of 100 days), which did not allow the development of more anaerobic pockets in PI than in PII, indicating that both piles had similar greenhouse gas impacts. Results for carbon dioxide were similar in both piles, with some differentiation appearing between the core and top placements compared to the side placement. Reduction of the decomposition rate further from the core and a typical windrow chimney effect (gases from the core flowing through the top) explain this similarity between placements. The similarity between piles can be explained by the similar amounts of easily decomposable organic matter found in both piles, indicating that the effect of the bulking agent ratio on the concentration of gases within the pile was not significant.

Evaluating the use of electrical resistivity imaging technique for improving CH(4) and CO(2) emission rate estimations in landfills

In order to improve the estimation of surface gas emissions in landfill, we evaluated a combination of geophysical and greenhouse gas measurement methodologies. Based on fifteen 2D electrical resistivity tomographies (ERTs), longitudinal cross section images of the buried waste layers were developed, identifying place and cross section size of organic waste (OW), organic waste saturated in leachates (SOW), low organic and non-organic waste. CH(4) and CO(2) emission measurements were then conducted using the static chamber technique at 5 surface points along two tomographies: (a) across a high-emitting area, ERT#2, where different amounts of relatively fresh OW and SOW were detected, and (b) across the oldest (at least eight years) cell in the landfill, ERT#6, with significant amounts of OW. Where the highest emission rates were recorded, they were strongly affected by the thickness of the OW and SOW fraction underneath each gas sampling point. The main reason for lower than expected values was the age of the layered buried waste. Lower than predicted emissions were also attributed to soil condition, which was the case at sampling points with surface ponding, i.e. surface accumulation of leachate (or precipitated water).

Biotechnology of flavonoids and other phenylpropanoid-derived natural products. Part II: Reconstruction of multienzyme pathways in plants and microbes

Plant natural products derived from phenylalanine and the phenylpropanoid pathways are impressive in their chemical diversity and are the result of plant evolution, which has selected for the acquisition of large repertoires of pigments, structural and defensive compounds, all derived from a phenylpropanoid backbone via the plant-specific phenylpropanoid pathway. These compounds are important in plant growth, development and responses to environmental stresses and thus can have large impacts on agricultural productivity. While plant-based medicines containing phenylpropanoid-derived active components have long been used by humans, the benefits of specific flavonoids and other phenylpropanoid-derived compounds to human health and their potential for long-term health benefits have only been recognized more recently. In this part of the review, we discuss in detail the recent strategies and achievements used in the reconstruction of multienzyme pathways in plants and microbes in an effort to be able to attain higher amounts of the desired flavonoids and stilbenoids exploiting their beneficial properties as analyzed extensively in Part I of this review.

Biotechnology of flavonoids and other phenylpropanoid-derived natural products. Part I: Chemical diversity, impacts on plant biology and human health

Plant natural products derived from phenylalanine and the phenylpropanoid pathway are impressive in their chemical diversity and are the result of plant evolution, which has selected for the acquisition of large repertoires of pigments, structural and defensive compounds, all derived from a phenylpropanoid backbone via the plant-specific phenylpropanoid pathway. These compounds are important in plant growth, development and responses to environmental stresses and thus can have large impacts on agricultural productivity. While plant-based medicines containing phenylpropanoid-derived active components have long been used by humans, the benefits of specific flavonoids and other phenylpropanoid-derived compounds to human health and their potential for long-term health benefits have been only recognized more recently. In this part of the review, we discuss the diversity and biosynthetic origins of phenylpropanoids and particularly of the flavonoid and stilbenoid natural products. We then review data pertaining to the modes of action and biological properties of these compounds, referring on their effects on human health and physiology and their roles as plant defense and antimicrobial compounds. This review continues in Part II discussing the use of biotechnological tools targeting the rational reconstruction of multienzyme pathways in order to modify the production of such compounds in plants and model microbial systems for the benefit of agriculture and forestry.