4-Vinylphenol biosynthesis from cellulose as the sole carbon source using phenolic acid decarboxylase- and tyrosine ammonia lyase-expressing Streptomyces lividans

Spectrophotometric and Fluorimetric High-Throughput Assays for Phenolic Acid Decarboxylase

Biocatalytic decarboxylation of hydroxycinnamic acids yields phenolic styrenes, which are important precursors for antioxidants, epoxy coatings, adhesives and other polymeric materials. Bacillus subtilis decarboxylase (BsPAD) is a cofactor-independent enzyme that catalyzes the cleavage of carbon dioxide from p-coumaric-, caffeic-, and ferulic acid with high catalytic efficiency. Real-time spectroscopic assays for decarboxylase reactions remove the necessity of extensive sample workup, which is required for HPLC, mass spectrometry, gas chromatography, or NMR methods. This work presents two robust and sensitive assays based on photometry and fluorimetry that allow decarboxylation reactions to be followed with high sensitivity while avoiding product extraction and long analysis times. Optimized assay procedures were used to measure BsPAD activity in cell lysates and to determine the kinetic constants (KM and Vmax ) of the purified enzyme for p-coumaric-, caffeic- and ferulic acid. Substrate inhibition was shown for caffeic acid.

Engineering a Pseudomonas taiwanensis 4-coumarate platform for production of para-hydroxy aromatics with high yield and specificity

Aromatics are valuable bulk or fine chemicals with a myriad of important applications. Currently, their vast majority is produced from petroleum associated with many negative aspects. The bio-based synthesis of aromatics contributes to the much-required shift towards a sustainable economy. To this end, microbial whole-cell catalysis is a promising strategy allowing the valorization of abundant feedstocks derived from biomass to yield de novo-synthesized aromatics. Here, we engineered tyrosine-overproducing derivatives of the streamlined chassis strain Pseudomonas taiwanensis GRC3 for efficient and specific production of 4-coumarate and derived aromatics. This required pathway optimization to avoid the accumulation of tyrosine or trans-cinnamate as byproducts. Although application of tyrosine-specific ammonia-lyases prevented the formation of trans-cinnamate, they did not completely convert tyrosine to 4-coumarate, thereby displaying a significant bottleneck. The use of a fast but unspecific phenylalanine/tyrosine ammonia-lyase from Rhodosporidium toruloides (RtPAL) alleviated this bottleneck, but caused phenylalanine conversion to trans-cinnamate. This byproduct formation was greatly reduced through the reverse engineering of a point mutation in prephenate dehydratase domain-encoding pheA. This upstream pathway engineering enabled efficient 4-coumarate production with a specificity of >95% despite using an unspecific ammonia-lyase, without creating an auxotrophy. In shake flask batch cultivations, 4-coumarate yields of up to 21.5% (Cmol/Cmol) from glucose and 32.4% (Cmol/Cmol) from glycerol were achieved. Additionally, the product spectrum was diversified by extending the 4-coumarate biosynthetic pathway to enable the production of 4-vinylphenol, 4-hydroxyphenylacetate, and 4-hydroxybenzoate with yields of 32.0, 23.0, and 34.8% (Cmol/Cmol) from glycerol, respectively.

Marine Actinomycetes, New Sources of Biotechnological Products

The Actinomycetales order is one of great genetic and functional diversity, including diversity in the production of secondary metabolites which have uses in medical, environmental rehabilitation, and industrial applications. Secondary metabolites produced by actinomycete species are an abundant source of antibiotics, antitumor agents, anthelmintics, and antifungals. These actinomycete-derived medicines are in circulation as current treatments, but actinomycetes are also being explored as potential sources of new compounds to combat multidrug resistance in pathogenic bacteria. Actinomycetes as a potential to solve environmental concerns is another area of recent investigation, particularly their utility in the bioremediation of pesticides, toxic metals, radioactive wastes, and biofouling. Other applications include biofuels, detergents, and food preservatives/additives. Exploring other unique properties of actinomycetes will allow for a deeper understanding of this interesting taxonomic group. Combined with genetic engineering, microbial experimental evolution, and other enhancement techniques, it is reasonable to assume that the use of marine actinomycetes will continue to increase. Novel products will begin to be developed for diverse applied research purposes, including zymology and enology. This paper outlines the current knowledge of actinomycete usage in applied research, focusing on marine isolates and providing direction for future research.

Recent advances in biocatalytic derivatization of L-tyrosine

L-Tyrosine is an aromatic, polar, non-essential amino acid that contains a highly reactive α-amino, α-carboxyl, and phenolic hydroxyl group. Derivatization of these functional groups can produce chemicals, such as L-3,4-dihydroxyphenylalanine, tyramine, 4-hydroxyphenylpyruvic acid, and benzylisoquinoline alkaloids, which are widely employed in the pharmaceutical, food, and cosmetics industries. In this review, we summarize typical L-tyrosine derivatizations catalyzed by enzymatic biocatalysts, as well as the strategies and challenges associated with their production processes. Finally, we discuss future perspectives pertaining to the enzymatic production of L-tyrosine derivatives.Key points• Summary of recent advances in enzyme-catalyzed L-tyrosine derivatization.• Highlights of relevant strategies involved in L-tyrosine derivatives biosynthesis.• Future perspectives on industrial applications of L-tyrosine derivatization.

Recent Advances in Metabolically Engineered Microorganisms for the Production of Aromatic Chemicals Derived From Aromatic Amino Acids

Aromatic compounds derived from aromatic amino acids are an important class of diverse chemicals with a wide range of industrial and commercial applications. They are currently produced via petrochemical processes, which are not sustainable and eco-friendly. In the past decades, significant progress has been made in the construction of microbial cell factories capable of effectively converting renewable carbon sources into value-added aromatics. Here, we systematically and comprehensively review the recent advancements in metabolic engineering and synthetic biology in the microbial production of aromatic amino acid derivatives, stilbenes, and benzylisoquinoline alkaloids. The future outlook concerning the engineering of microbial cell factories for the production of aromatic compounds is also discussed.

Characterization of two new aromatic amino acid lyases from actinomycetes for highly efficient production of p-coumaric acid

p-Coumaric acid (p-CA) is a bioactive natural product and an important industrial material for pharmaceuticals and nutraceuticals. It can be synthesized from deamination of L-tyrosine by tyrosine ammonia lyase (TAL). In this work, we discovered two aromatic amino acid lyase genes, Sas-tal and Sts-tal, from Saccharothrix sp. NRRL B-16348 and Streptomyces sp. NRRL F-4489, respectively, and expressed them in Escherichia coli BL21(DE3). The two enzymes were functionally characterized as TAL. The optimum reaction temperature for Sas-TAL and Sts-TAL is 55 °C and 50 °C, respectively; while, the optimum pH for both TALs is 11. Sas-TAL had a k_cat/K_m value of 6.2 μM^-1 min^-1, while Sts-TAL had a much higher efficiency with a k_cat/K_m value of 78.3 μM^-1 min^-1. Both Sts-TAL and Sas-TAL can also take L-phenylalanine as the substrate to yield trans-cinnamic acid, and Sas-TAL showed much higher phenylalanine ammonia lyase activity than Sts-TAL. Using E. coli/Sts-TAL as a whole-cell biocatalyst, the productivity of p-CA reached 2.88 ± 0.12 g (L h)^-1, which represents the highest efficiency for microbial production of p-CA. Therefore, this work not only reports the identification of two new TALs from actinomycetes, but also provides an efficient way to produce the industrially valuable material p-CA.

Metabolic engineering of microorganisms for production of aromatic compounds

Metabolic engineering has been enabling development of high performance microbial strains for the efficient production of natural and non-natural compounds from renewable non-food biomass. Even though microbial production of various chemicals has successfully been conducted and commercialized, there are still numerous chemicals and materials that await their efficient bio-based production. Aromatic chemicals, which are typically derived from benzene, toluene and xylene in petroleum industry, have been used in large amounts in various industries. Over the last three decades, many metabolically engineered microorganisms have been developed for the bio-based production of aromatic chemicals, many of which are derived from aromatic amino acid pathways. This review highlights the latest metabolic engineering strategies and tools applied to the biosynthesis of aromatic chemicals, many derived from shikimate and aromatic amino acids, including L-phenylalanine, L-tyrosine and L-tryptophan. It is expected that more and more engineered microorganisms capable of efficiently producing aromatic chemicals will be developed toward their industrial-scale production from renewable biomass.

Terminal Alkenes from Acrylic Acid Derivatives via Non-Oxidative Enzymatic Decarboxylation by Ferulic Acid Decarboxylases

Fungal ferulic acid decarboxylases (FDCs) belong to the UbiD-family of enzymes and catalyse the reversible (de)carboxylation of cinnamic acid derivatives through the use of a prenylated flavin cofactor. The latter is synthesised by the flavin prenyltransferase UbiX. Herein, we demonstrate the applicability of FDC/UbiX expressing cells for both isolated enzyme and whole-cell biocatalysis. FDCs exhibit high activity with total turnover numbers (TTN) of up to 55000 and turnover frequency (TOF) of up to 370 min-1. Co-solvent compatibility studies revealed FDC's tolerance to some organic solvents up 20 % v/v. Using the in-vitro (de)carboxylase activity of holo-FDC as well as whole-cell biocatalysts, we performed a substrate profiling study of three FDCs, providing insights into structural determinants of activity. FDCs display broad substrate tolerance towards a wide range of acrylic acid derivatives bearing (hetero)cyclic or olefinic substituents at C3 affording conversions of up to >99 %. The synthetic utility of FDCs was demonstrated by a preparative-scale decarboxylation.

Production of chemicals and proteins using biomass-derived substrates from a Streptomyces host

Bioproduction using microbes from biomass feedstocks is of interest in regards to environmental problems and cost reduction. Streptomyces as an industrial microorganism plays an important role in the production of useful secondary metabolites for various applications. This strain also secretes a wide range of extracellular enzymes which degrade various biopolymers in nature, and it consumes these degrading substrates as nutrients. Hence, Streptomyces can be employed as a cell factory for the conversion of biomass-derived substrates into various products. This review focuses on the following two points: (1) Streptomyces as a producer of enzymes for degrading biomass-derived polysaccharides and polymers; and, (2) wild-type and engineered strains of Streptomyces as a host for chemical production from biomass-derived substrates.

Evolution and Ecology of Actinobacteria and Their Bioenergy Applications

The ancient phylum Actinobacteria is composed of phylogenetically and physiologically diverse bacteria that help Earth's ecosystems function. As free-living organisms and symbionts of herbivorous animals, Actinobacteria contribute to the global carbon cycle through the breakdown of plant biomass. In addition, they mediate community dynamics as producers of small molecules with diverse biological activities. Together, the evolution of high cellulolytic ability and diverse chemistry, shaped by their ecological roles in nature, make Actinobacteria a promising group for the bioenergy industry. Specifically, their enzymes can contribute to industrial-scale breakdown of cellulosic plant biomass into simple sugars that can then be converted into biofuels. Furthermore, harnessing their ability to biosynthesize a range of small molecules has potential for the production of specialty biofuels.

Recent Advances in Microbial Production of Aromatic Chemicals and Derivatives

Along with the development of metabolic engineering and synthetic biology tools, various microbes are being used to produce aromatic chemicals. In microbes, aromatics are mainly produced via a common important precursor, chorismate, in the shikimate pathway. Natural or non-natural aromatics have been produced by engineering metabolic pathways involving chorismate. In the past decade, novel approaches have appeared to produce various aromatics or to increase their productivity, whereas previously, the targets were mainly aromatic amino acids and the strategy was deregulating feedback inhibition. In this review, we summarize recent studies of microbial production of aromatics based on metabolic engineering approaches. In addition, future perspectives and challenges in this research area are discussed.

Efficient evaluation of cellulose digestibility by Trichoderma reesei Rut-C30 cultures in online monitored shake flasks

Background

Pretreated lignocellulosic biomass is considered as a suitable feedstock for the sustainable production of chemicals. However, the recalcitrant nature of cellulose often results in very cost-intensive overall production processes. A promising concept to reduce the costs is consolidated bioprocessing, which integrates in a single step cellulase production, cellulose hydrolysis, and fermentative conversion of produced sugars into a valuable product. This approach, however, requires assessing the digestibility of the applied celluloses and, thus, the released sugar amount during the fermentation. Since the released sugars are completely taken up by Trichoderma reesei Rut-C30 and the sugar consumption is stoichiometrically coupled to oxygen uptake, the respiration activity was measured to evaluate the digestibility of cellulose.

Results

The method was successfully tested on commercial cellulosic substrates identifying a correlation between the respiration activity and the crystallinity of the substrate. Pulse experiments with cellulose and cellulases suggested that the respiration activity of T. reesei on cellulose can be divided into two distinct phases, one limited by enzyme activity and one by cellulose-binding-sites. The impact of known (cellobiose, sophorose, urea, tween 80, peptone) and new (miscanthus steepwater) compounds enhancing cellulase production was evaluated. Furthermore, the influence of two different pretreatment methods, the OrganoCat and OrganoSolv process, on the digestibility of beech wood saw dust was tested.

Conclusions

The introduced method allows an online evaluation of cellulose digestibility in complex and non-complex cultivation media. As the measurements are performed under fermentation conditions, it is a valuable tool to test different types of cellulose for consolidated bioprocessing applications. Furthermore, the method can be applied to identify new compounds, which influence cellulase production.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0567-7) contains supplementary material, which is available to authorized users.

Styrene production from a biomass-derived carbon source using a coculture system of phenylalanine ammonia lyase and phenylacrylic acid decarboxylase-expressing Streptomyces lividans transformants

To produce styrene from a biomass-derived carbon source, Streptomyces lividans was adopted as a host strain. The gene encoding ferulic acid decarboxylase from Saccharomyces cerevisiae (FDC1) was introduced into S. lividans, and the resulting S. lividans transformant successfully expressed FDC1 and converted trans-cinnamic acid (CA) to styrene. A key factor in styrene production using microbes is the recovery of volatile styrene. In the present study, we selected polystyrene resin beads XRD-4 as the absorbent agent to recover styrene produced using S. lividans transformants, which enabled recovery of styrene from the culture broth. For styrene production from biomass-derived carbon sources, S. lividans/FDC1 was cultured together with S. lividans/p-encP, which we previously reported as a CA-producing S. lividans strain. This coculture system combined with the recovery of styrene using XAD-4 allowed the production of styrene from glucose, cellobiose, or xylo-oligosaccharide, respectively.