Terpenoid biosynthesis in prokaryotes

Contribution of the gonococcal NEIS1446-ispD gene conversion to the pathobiology of the Neisseria meningitidis urethritis clade, NmUC

Over the last decade, a Neisseria meningitidis (Nm) urethritis-causing clade (NmUC) has emerged to cause clusters of meningococcal urethritis in the United States and globally. One genomic signature of NmUC is the integration of Neisseria gonorrhoeae (Ng) DNA in an operon, NEIS1446-NEIS1438, which partially replaced the Nm ispD gene. IspD is the 2-C-methyl-d-erythritol 4-phosphate cytidylyltransferase of the terpenoid precursor synthesis pathway, required for the production of ubiquinones of the electron transfer chain. IspD is essential in several gram-negative bacteria. The biological importance of the NEIS1446-ispD gene conversion event for NmUC was investigated. The ispD gene was found to be essential in NmUC (CNM3) and non-clade Nm (MC58), and a mutation at the native locus can only be made with the insertion of a second ispD copy in the genome. The IspDMC58 variant was more efficient at promoting aerobic growth at a low level than IspDCNM3; the two proteins differ by 15 residues. Maximal aerobic growth densities of strains with an NmUC background resembled Ng (FA19), and both were significantly lower than Nm. In contrast to non-clade Nm, all NmUC strains survived well anaerobically. Increasing ispD expression by titrating IPTG in non-clade Nm enhanced anaerobic survival. Translational reporters of the NmUC and Ng promoters demonstrated similar expression levels, and both were significantly higher than non-clade Nm, under aerobic and microaerobic conditions. Our findings suggest that the integration of gonococcal DNA into the NEIS1446-NEIS1438 operon of NmUC has increased ispD expression, contributing to NmUC's adaptation to the oxygen-limited environment of the human urogenital tract.

Combining culture optimization and synthetic biology to improve production and detection of secondary metabolites in Myxococcus xanthus: application to myxoprincomide

Microbial secondary metabolites play crucial ecological roles in governing species interactions and contributing to their defense strategies. Their unique structures and potent bioactivities have been key in discovering antibiotics and anticancer drugs. Genome sequencing has undoubtedly revealed that myxobacteria constitute a huge reservoir of secondary metabolites as the well-known producers, actinomycetes. However, because most secondary metabolites are not produced in the laboratory context, the natural products from myxobacteria characterized to date represent only the tip of the iceberg. By combining the engineering of a dedicated Myxococcus xanthus DZ2 chassis strain with a two-step growth medium protocol, we provide a new approach called two-step Protocol for Resource Integration and Maximization-Biomolecules Overproduction and Optimal Screening Therapeutics (2PRIM-BOOST) for the production of non-ribosomal peptides synthetases (NRPS)/polyketides synthases (PKS) secondary metabolites from myxobacteria. We further show that the 2PRIM-BOOST strategy will facilitate the screening of secondary metabolites for biological activities of medical interest. As proof of concept, using a constitutive strong promoter, the myxoprincomide from M. xanthus DZ2 has been efficiently produced and its biosynthesis has been enhanced using the 2PRIM-BOOST approach, allowing the identification of new features of myxoprincomide. This strategy should allow the chances to produce and discover new NRPS, PKS, and mixed NRPS/PKS hybrid natural metabolites that are currently considered as cryptic and are the most represented in myxobacteria.IMPORTANCEMicrobial secondary metabolites are important in species interactions and are also a prolific source of drugs. Myxobacteria are ubiquitous soil-dwelling bacteria constituting a huge reservoir of secondary metabolites. However, because most of these molecules are not produced in the laboratory context, one can estimate that only one-tenth have been characterized to date. Here, we developed a new strategy called two-step Protocol for Resource Integration and Maximization-Biomolecules Overproduction and Optimal Screening Therapeutics (2PRIM-BOOST) that combines the engineering of a dedicated Myxococcus xanthus chassis strain together with growth medium optimization. By combining these strategies with the insertion of a constitutive promoter upstream the biosynthetic gene cluster (BGC), the production of myxoprincomide, a characterized low-produced secondary metabolite, was successfully and significantly increased. The 2PRIM-BOOST enriches the toolbox used to produce previously cryptic metabolites, unveil their ecological role, and provide new molecules of medical interest.

Development of a Golden Gate Assembly-Based Genetic Toolbox for Lactiplantibacillus plantarum and Its Application for Engineering Monoterpenoid Biosynthesis

Lactiplantibacillus plantarum is a food-grade lactic acid bacterium widely used in the food and beverage industry. Recently, this probiotic organism has been applied as a biofactory for the production of pharmaceutical and food-related compounds, but existing promoters and expression vectors for the genetic engineering of L. plantarum rely on inefficient cloning strategies and are usually not well-characterized. We therefore developed a modular and standardized Golden Gate Assembly-based toolbox for the de novo assembly of shuttle vectors from Escherichia coli to L. plantarum. A collection of the most relevant genetic parts, e.g., different origins of replication and promoters, was incorporated in our toolbox and thoroughly characterized by flow cytometry and the fluorescence assay. Standardized fusion sites allow combining the genetic part freely into a plasmid in one step. This approach allows for the high-throughput assembly of numerous constructs in a standardized genetic context, thus improving the efficiency and predictability of metabolic engineering in L. plantarum. Using our toolbox, we were able to produce the aroma compounds linalool and geraniol in L. plantarum by extending its native mevalonate pathway with plant-derived monoterpenoid synthases.

Theaflavin-3,3'-digallate effectively attenuates biofilm formation by Enterococcus faecalis via the targeting of specific quorum sensing pathways

Enterococcus faecalis, an opportunistic pathogen responsible for nosocomial infections, exhibits increased pathogenicity via biofilm formation. Theaflavin-3,3'-digallate (TF3), a theaflavin extracted from black tea, exhibits potent antibacterial effects. In the present study, we investigated the inhibitory effect of TF3 on E. faecalis. Our results indicated that TF3 significantly inhibited E. faecalis ATCC 29212 biofilm formation. This observation was further confirmed via crystal violet staining, confocal laser scanning microscopy, and field emission-scanning electron microscopy. To disclose the underlying mechanisms, RNA-seq was applied. TF3 treatment significantly altered the transcriptomic profile of E. faecalis, as evidenced by identification of 248 differentially expressed genes (DEGs). Through functional annotation of these DEGs, several quorum-sensing pathways were found to be suppressed in TF3-treated cultures. Further, gene expression verification via real-time PCR confirmed the downregulation of gelE, sprE, and secY by TF3. These findings highlighted the ability of TF3 to impede E. faecalis biofilm formation, suggesting a novel preventive strategy against E. faecalis infections.

Jeongeuplla avenae gen. nov., sp. nov., a novel β-carotene-producing bacterium that alleviates salinity stress in Arabidopsis

A novel endophytic bacterium, designated DY-R2A-6T, was isolated from oat (Avena sativa L.) seeds and found to produces β-carotene. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain DY-R2A-6T had 96.3% similarity with Jiella aquimaris LZB041T, 96.0% similarity with Aurantimonas aggregate R14M6T and Aureimonas frigidaquae JCM 14755T, and less than 95.8% similarity with other genera in the family Aurantimonadaceae. The complete genome of strain DY-R2A-6T comprised 5,929,370 base pairs, consisting of one full chromosome (5,909,198 bp) and one plasmid (20,172 bp), with a G + C content was 69.1%. The overall genome-related index (OGRI), including digital DNA-DNA hybridization (<20.5%), ANI (<79.2%), and AAI (<64.2%) values, all fell below the thresholds set for novel genera. The major cellular fatty acids (>10%) of strain DY-R2A-6T were C16:0, C19:0 cyclo ω8c, and summed feature 8 (C18:1ω7c and/or C18:1ω6c). Ubiquinone-10 was the main respiratory quinone. We identified the gene cluster responsible for carotenoid biosynthesis in the genome and found that the pink-pigment produced by strain DY-R2A-6T is β-carotene. In experiment with Arabidopsis seedlings, co-cultivation with strain DY-R2A-6T led to a 1.4-fold increase in plant biomass and chlorophyll content under salt stress conditions, demonstrating its capacity to enhance salt stress tolerance in plants. Moreover, external application of β-carotene to Arabidopsis seedlings under salt stress conditions also mitigated the stress significantly. Based on these findings, strain DY-R2A-6T is proposed to represent a novel genus and species in the family Aurantimonadaceae, named Jeongeuplla avenae gen. nov., sp. nov. The type strain is DY-R2A-6T (= KCTC 82985T = GDMCC 1.3014T). This study not only identified a new taxon but also utilized genome analysis to predict and confirm the production of β-carotene by strain DY-R2A-6T. It also demonstrated the ability of this strain to enhance salt stress tolerance in plants, suggesting potential application in agriculture to mitigate environmental stress in crops.

Integrated transcriptomic and metabolomic analyses revealed the molecular mechanism of terpenoid formation for salicylic acid resistance in Pulsatilla chinensis callus

As a kind of traditional Chinese medicine, Pulsatilla chinensis (Bunge) Regel is well known for its anti-inflammation and anti-cancer activities, which are attributed to its active components including total saponins and monomers. To clarify the synthesis and metabolism mechanisms of class components in callus terpenes of P. chinensis, a certain concentration of salicylic acid (SA) hormone elicitor was added to the callus before being analysed by transcriptomic and metabolomic techniques. Results showed that the content of Pulsatilla saponin B4 in the callus suspension culture was significantly increased up to 1.99% with the addition of SA. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the differentially expressed genes were mainly enriched in 122 metabolic pathways, such as terpenoid metabolism-related pathways: terpenoid skeleton synthesis pathway, monoterpenoid biosynthesis pathways, diterpenoid biosynthesis pathways, and ubiquinone and other terpenoid-quinone biosynthesis pathways. A total of 31 differentially accumulated metabolites were obtained from four differential groups. Amongst 21 kinds of known chemical components in P. chinensis, deoxyloganic acid was the only monoterpenoid; the others are triterpenoids. In summary, this study found that SA elicitors can affect the metabolic changes of terpenoids in P. chinensis callus, which provided a basis for analysing the genetic regulation of terpenoid components of leucons.

Amoxicillin-resistant Streptococcus pneumoniae can be resensitized by targeting the mevalonate pathway as indicated by sCRilecs-seq

Antibiotic resistance in the important opportunistic human pathogen Streptococcus pneumoniae is on the rise. This is particularly problematic in the case of the β-lactam antibiotic amoxicillin, which is the first-line therapy. It is therefore crucial to uncover targets that would kill or resensitize amoxicillin-resistant pneumococci. To do so, we developed a genome-wide, single-cell based, gene silencing screen using CRISPR interference called sCRilecs-seq (subsets of CRISPR interference libraries extracted by fluorescence activated cell sorting coupled to next generation sequencing). Since amoxicillin affects growth and division, sCRilecs-seq was used to identify targets that are responsible for maintaining proper cell size. Our screen revealed that downregulation of the mevalonate pathway leads to extensive cell elongation. Further investigation into this phenotype indicates that it is caused by a reduced availability of cell wall precursors at the site of cell wall synthesis due to a limitation in the production of undecaprenyl phosphate (Und-P), the lipid carrier that is responsible for transporting these precursors across the cell membrane. The data suggest that, whereas peptidoglycan synthesis continues even with reduced Und-P levels, cell constriction is specifically halted. We successfully exploited this knowledge to create a combination treatment strategy where the FDA-approved drug clomiphene, an inhibitor of Und-P synthesis, is paired up with amoxicillin. Our results show that clomiphene potentiates the antimicrobial activity of amoxicillin and that combination therapy resensitizes amoxicillin-resistant S. pneumoniae. These findings could provide a starting point to develop a solution for the increasing amount of hard-to-treat amoxicillin-resistant pneumococcal infections.

Complex and flexible catabolism in Aromatoleum aromaticum pCyN1

Large quantities of organic matter are continuously deposited, and (a)biotic gradients intersect in the soil-rhizosphere, where biodegradation contributes to the global cycles of elements. The betaproteobacterial genus Aromatoleum comprises cosmopolitan, facultative denitrifying degradation specialists. A. aromaticum pCyN1 stands out for anaerobically decomposing plant-derived monoterpenes in addition to monoaromatic hydrocarbons, polar aromatics and aliphatics. The catabolic network's structure and flexibility in A. aromaticum pCyN1 was studied across 34 growth conditions by superimposing proteome profiles onto the manually annotated 4.37 Mbp genome. Strain pCyN1 employs three fundamentally different enzymes for C-H-bond cleavage at the methyl groups of p-cymene/4-ethyltoluene, toluene and p-cresol, respectively. Regulation of degradation modules displayed substrate specificities ranging from narrow (toluene and cyclohexane carboxylate) via medium-wide (one module shared by p-cymene, 4-ethyltoluene, α-phellandrene, α-terpinene, γ-terpinene and limonene) to broad (central benzoyl-CoA pathway serving 16 aromatic substrates). Remarkably, three variants of ATP-dependent (class I) benzoyl-CoA reductase and four different β-oxidation routes establish a degradation hub that accommodates the substrate diversity. The respiratory system displayed several conspicuous profiles, e.g., the presence of nitrous oxide reductase under oxic and of low-affinity oxidase under anoxic conditions. Overall, nutritional versatility in conjunction with network regulation endow A. aromaticum pCyN1 with broad adaptability. This article is protected by copyright. All rights reserved.

Genome-wide screening antifungal genes in Streptomyces griseus S4-7, a Fusarium wilt disease suppressive microbial agent

Streptomyces is a widely studied bacterial genus, particularly with regard to secondary metabolites and antibiotics production. Streptomyces griseus S4-7 was isolated from a strawberry Fusarium wilt disease suppressive soil, and its biological control ability has been well established. However, the antifungal mechanism of strain S4-7 is not yet fully understood at the molecular and biochemical level. Therefore, in this study we created a random mutant library for strain S4-7 with the Tn5 transposon element to investigate antifungal traits on a genome-wide scale. In total 4646 individual mutant strains were created and 13 mutants were selected based on loss of antifungal activity. The knockout genes were identified as electron transfer oxidoreductase (eto),sigma factor-70(sig70) and nrps by Inverse PCR (I-PCR). eto regulates the geranylgeranyl reductase gene, which is involved in terpenoid-quinone biosynthesis, an important factor in cell fitness. In the △eto strain, expression of wbl, a master regulator of the production of secondary metabolites, was significantly reduced. sig70 is responsible for the cell differentiation sensing mechanism in genus Streptomyces. △nrps showed decreased production of hybrid peptide-polyketide siderophores. These results suggest that S. griseus S4-7 may have various antifungal mechanisms, and each mechanism is essential to maximal antifungal activity.

Engineered Rhodobacter capsulatus as a Phototrophic Platform Organism for the Synthesis of Plant Sesquiterpenoids

Sesquiterpenoids are a large class of natural compounds offering manifold properties valuable for food, cosmetics, agriculture, and pharma industry. Production in microorganisms is a sustainable approach to provide sesquiterpenoids for research and industrial use independent of their natural sources. This requires the functional transfer of the respective biocatalytic pathways in an adequate host microorganism offering a sufficient supply of precursors that is ideally adjusted to the individual demand of the recombinant biosynthesis route. The phototrophic purple bacterium Rhodobacter capsulatus offers unique physiological properties that are favorable for biosynthesis of hydrophobic terpenes. Under phototrophic conditions, it develops a large intracytoplasmic membrane suitable for hosting membrane-bound enzymes and metabolites of respective biosynthetic pathways. In addition, Rhodobacter harbors an intrinsic carotenoid biosynthesis that can be engineered toward the production of foreign terpenes. Here, we evaluate R. capsulatus as host for the production of plant sesquiterpenoids under phototrophic conditions using patchoulol and valencene as a proof of concept. The heterologous expression of patchoulol synthase PcPS from Pogostemon cablin as well as the valencene synthases CsVS from Citrus sinensis and CnVS from Callitropsis nootkatensis led to the production of the respective sesquiterpenoids in R. capsulatus. To analyze, if gradually adjustable formation of the key precursor farnesylpyrophosphate (FPP) is beneficial for sesquiterpene synthesis under phototrophic conditions, the intrinsic 1-deoxy-D-xylulose 5-phosphate (DXP) pathway genes as well as the heterologous mevalonate pathway genes were modularly expressed in various combinations. To this end, different plasmids and chromosomally integrated expression tools were developed harboring the strong and tightly controlled P_nif promoter for heterologous gene expression. Notably, comparative studies identified a distinct combination of precursor biosynthetic genes as best-performing setup for each of the tested sesquiterpene synthases. In summary, we could demonstrate that R. capsulatus is a promising alternative platform organism that is suited for sustainable sesquiterpenoid formation under phototrophic cultivation conditions. A modular engineering of R. capsulatus strains via tailored co-expression of FPP biosynthetic genes further allowed adaptation of sesquiterpene precursor formation to its catalytic conversion by different plant terpene synthases.

Substrate Specificity and Engineering of Mevalonate 5-Phosphate Decarboxylase

A bifurcation of the mevalonate (MVA) pathway was recently discovered in bacteria of the Chloroflexi phylum. In this alternative route for the biosynthesis of isopentenylpyrophosphate (IPP), the penultimate step is the decarboxylation of (R)-mevalonate 5-phosphate ((R)-MVAP) to isopentenyl phosphate (IP), which is followed by the ATP-dependent phosphorylation of IP to IPP catalyzed by isopentenyl phosphate kinase (IPK). Notably, the decarboxylation reaction is catalyzed by mevalonate 5-phosphate decarboxylase (MPD), which shares considerable sequence similarity with mevalonate diphosphate decarboxylase (MDD) of the classical MVA pathway. We show that an enzyme originally annotated as an MDD from the Chloroflexi bacterium Anaerolinea thermophila possesses equal catalytic efficiency for (R)-MVAP and (R)-mevalonate 5-diphosphate ((R)-MVAPP). Further, the molecular basis for this dual specificity is revealed by near atomic-resolution X-ray crystal structures of A. thermophila MPD/MDD bound to (R)-MVAP or (R)-MVAPP. These findings, when combined with sequence and structural comparisons of this bacterial enzyme, functional MDDs, and several putative MPDs, delineate key active-site residues that confer substrate specificity and functionally distinguish MPD and MDD enzyme classes. Extensive sequence analyses identified functional MPDs in the halobacteria class of archaea that had been annotated as MDDs. Finally, no eukaryotic MPD candidates were identified, suggesting the absence of the alternative MVA (altMVA) pathway in all eukaryotes, including, paradoxically, plants, which universally encode a structural and functional homologue of IPK. Additionally, we have developed a viable engineered strain of Saccharomyces cerevisiae as an in vivo metabolic model and a synthetic biology platform for enzyme engineering and terpene biosynthesis in which the classical MVA pathway has been replaced with the altMVA pathway.

Limonene dehydrogenase hydroxylates the allylic methyl group of cyclic monoterpenes in the anaerobic terpene degradation by Castellaniella defragrans

The enzymatic functionalization of hydrocarbons is a central step in the global carbon cycle initiating the mineralization of methane, isoprenes, and monoterpenes, the most abundant biologically produced hydrocarbons. Also, terpene-modifying enzymes have found many applications in the energy-economic biotechnological production of fine chemicals. Here, we describe a limonene dehydrogenase that was purified from the facultatively anaerobic betaproteobacterium Castellaniella defragrans 65Phen grown on monoterpenes under denitrifying conditions in the absence of molecular oxygen. The purified limonene:ferrocenium oxidoreductase activity hydroxylated the methyl group of limonene (1-methyl-4-(1-methylethenyl)-cyclohex-1-ene) yielding perillyl alcohol ([4-(prop-1-en-2-yl)cyclohex-1-en-1-yl]methanol). The enzyme had a DTT:perillyl alcohol oxidoreductase activity yielding limonene. Mass spectrometry and molecular size determinations revealed a heterodimeric enzyme comprising CtmA and CtmB. Recently, the two proteins had been identified by transposon mutagenesis and proteomics as part of the cyclic terpene metabolism (ctm) in C. defragrans and are annotated as FAD-dependent oxidoreductases of the protein domain family phytoene dehydrogenases and related proteins (COG1233). CtmAB is the first heterodimeric enzyme in this protein superfamily. Flavins in the purified CtmAB are oxidized by ferrocenium and are reduced by limonene. Heterologous expression of CtmA, CtmB, and CtmAB in Escherichia coli demonstrated that limonene dehydrogenase activity required both subunits, each carrying a flavin cofactor. Native CtmAB oxidized a wide range of monocyclic monoterpenes containing the allylic methyl group motif (1-methyl-cyclohex-1-ene). In conclusion, we have identified CtmAB as a hydroxylating limonene dehydrogenase and the first heteromer in a family of FAD-dependent dehydrogenases acting on allylic methylene or methyl CH-bonds. We suggest placing in Enzyme Nomenclature as new entry EC 1.17.99.8.

Microbial Cell Factories for the Production of Terpenoid Flavor and Fragrance Compounds

Terpenoid flavor and fragrance compounds are of high interest to the aroma industry. Microbial production offers an alternative sustainable access to the desired terpenoids independent of natural sources. Genetically engineered microorganisms can be used to synthesize terpenoids from cheap and renewable resources. Due to its modular architecture, terpenoid biosynthesis is especially well suited for the microbial cell factory concept: a platform host engineered for a high flux toward the central C₅ prenyl diphosphate precursors enables the production of a broad range of target terpenoids just by varying the pathway modules converting the C₅ intermediates to the product of interest. In this review typical terpenoid flavor and fragrance compounds marketed or under development by biotech and aroma companies are given, and the specificities of the aroma market are discussed. The main part of this work focuses on key strategies and recent advances to engineer microbes to become efficient terpenoid producers.

Mevalonate 5-diphosphate mediates ATP binding to the mevalonate diphosphate decarboxylase from the bacterial pathogen Enterococcus faecalis

The mevalonate pathway produces isopentenyl diphosphate (IPP), a building block for polyisoprenoid synthesis, and is a crucial pathway for growth of the human bacterial pathogen Enterococcus faecalis The final enzyme in this pathway, mevalonate diphosphate decarboxylase (MDD), acts on mevalonate diphosphate (MVAPP) to produce IPP while consuming ATP. This essential enzyme has been suggested as a therapeutic target for the treatment of drug-resistant bacterial infections. Here, we report functional and structural studies on the mevalonate diphosphate decarboxylase from E. faecalis (MDD_EF). The MDD_EF crystal structure in complex with ATP (MDD_EF-ATP) revealed that the phosphate-binding loop (amino acids 97-105) is not involved in ATP binding and that the phosphate tail of ATP in this structure is in an outward-facing position pointing away from the active site. This suggested that binding of MDD_EF to MVAPP is necessary to guide ATP into a catalytically favorable position. Enzymology experiments show that the MDD_EF performs a sequential ordered bi-substrate reaction with MVAPP as the first substrate, consistent with the isothermal titration calorimetry (ITC) experiments. On the basis of ITC results, we propose that this initial prerequisite binding of MVAPP enhances ATP binding. In summary, our findings reveal a substrate-induced substrate-binding event that occurs during the MDD_EF-catalyzed reaction. The disengagement of the phosphate-binding loop concomitant with the alternative ATP-binding configuration may provide the structural basis for antimicrobial design against these pathogenic enterococci.

Challenges and Hallmarks of Establishing Alkylacetylphosphonates as Probes of Bacterial 1-Deoxy-d-xylulose 5-Phosphate Synthase

1-Deoxy-d-xylulose 5-phosphate (DXP) synthase catalyzes the thiamin diphosphate (ThDP)-dependent formation of DXP from pyruvate and d-glyceraldehyde 3-phosphate. DXP is at a metabolic branch point in bacteria, feeding into the methylerythritol phosphate pathway to indispensable isoprenoids and acting as a precursor for biosynthesis of essential cofactors in central metabolism, pyridoxal phosphate and ThDP, the latter of which is also required for DXP synthase catalysis. DXP synthase follows a unique random sequential mechanism and possesses an unusually large active site. These features have guided the design of sterically demanding alkylacetylphosphonates (alkylAPs) toward the development of selective DXP synthase inhibitors. alkylAPs studied here display selective, low μM inhibitory activity against DXP synthase. They are weak inhibitors of bacterial growth in standard nutrient rich conditions. However, bacteria are significantly sensitized to most alkylAPs in defined minimal growth medium, with minimal inhibitory concentrations (MICs) ranging from low μM to low mM and influenced by alkyl-chain length. The longest analog (C₈) displays the weakest antimicrobial activity and is a substrate for efflux via AcrAB-TolC. The dependence of inhibitor potency on growth environment emphasizes the need for antimicrobial screening conditions that are relevant to the in vivo microbial microenvironment during infection. DXP synthase expression and thiamin supplementation studies offer support for DXP synthase as an intracellular target for some alkylAPs and reveal both the challenges and intriguing aspects of these approaches to study target engagement.

Carotenoid Biosynthesis in Fusarium

Many fungi of the genus Fusarium stand out for the complexity of their secondary metabolism. Individual species may differ in their metabolic capacities, but they usually share the ability to synthesize carotenoids, a family of hydrophobic terpenoid pigments widely distributed in nature. Early studies on carotenoid biosynthesis in Fusariumaquaeductuum have been recently extended in Fusarium fujikuroi and Fusarium oxysporum, well-known biotechnological and phytopathogenic models, respectively. The major Fusarium carotenoid is neurosporaxanthin, a carboxylic xanthophyll synthesized from geranylgeranyl pyrophosphate through the activity of four enzymes, encoded by the genes carRA, carB, carT and carD. These fungi produce also minor amounts of β-carotene, which may be cleaved by the CarX oxygenase to produce retinal, the rhodopsin's chromophore. The genes needed to produce retinal are organized in a gene cluster with a rhodopsin gene, while other carotenoid genes are not linked. In the investigated Fusarium species, the synthesis of carotenoids is induced by light through the transcriptional induction of the structural genes. In some species, deep-pigmented mutants with up-regulated expression of these genes are affected in the regulatory gene carS. The molecular mechanisms underlying the control by light and by the CarS protein are currently under investigation.

Microbial alkane production for jet fuel industry: motivation, state of the art and perspectives

Bio‐jet fuel has attracted a lot of interest in recent years and has become a focus for aircraft and engine manufacturers, oil companies, governments and researchers. Given the global concern about environmental issues and the instability of oil market, bio‐jet fuel has been identified as a promising way to reduce the greenhouse gas emissions from the aviation industry, while also promoting energy security. Although a number of bio‐jet fuel sources have been approved for manufacture, their commercialization and entry into the market is still a far way away. In this review, we provide an overview of the drivers for intensified research into bio‐jet fuel technologies, the type of chemical compounds found in bio‐jet fuel preparations and the current state of related pre‐commercial technologies. The biosynthesis of hydrocarbons is one of the most promising approaches for bio‐jet fuel production, and thus we provide a detailed analysis of recent advances in the microbial biosynthesis of hydrocarbons (with a focus on alkanes). Finally, we explore the latest developments and their implications for the future of research into bio‐jet fuel technologies.