Accumulation of prenyl alcohols by terpenoid biosynthesis inhibitors in various microorganisms

Analysis of Microbial Community, Volatile Flavor Compounds, and Flavor of Cigar Tobacco Leaves From Different Regions

Despite the booming international trade in cigar tobacco leaves (CTLs), the main characteristics of tobacco leaves from different producing areas are rarely reported. This study aimed to characterize the microbial community, volatile flavor compounds (VFCs), and flavor of CTLs from four famous cigar-producing areas, including Dominica, Brazil, Indonesia, and China. High-throughput sequencing results showed that the dominant genera in CTLs were Staphylococcus, Pseudomonas, Aspergillus, Sampaiozyma, and Alternaria. Sensory analysis revealed that Indonesian and Chinese CTLs were characterized by leathery, peppery, and baked aroma. Brazilian CTLs were dominated by caramel and herb aroma. Dominican CTLs had aromas of milk, fruity, sour, cream, flower, nutty, and honey. Supplemented with the determination of volatile flavor compounds (VFCs), the flavor of CTLs could be scientifically quantified. Most of these VFCs were aldehydes and ketones, and 20 VFCs showed significant differences in CTLs from different regions. The microbial community, VFCs, and flavor of CTLs vary widely due to geographic differences. Network analysis revealed the microbial community was closely related to most VFCs, but the relationships between the fungal community and VFCs were less than the bacterial community, and most of them were negative. Furthermore, it also found that the bacterial community had a greater contribution to the flavor of CTLs than the fungal community. This study obtained essential information on CTLs, which laid a foundation for deeply excavating the relationship between microbes and VFCs and flavor, and establishing a tobacco information database.

Increasing the intracellular isoprenoid pool in Saccharomyces cerevisiae by structural fine-tuning of a bifunctional farnesyl diphosphate synthase

Farnesyl diphosphate synthase (FPPS) is a key enzyme responsible for the supply of isoprenoid precursors for several essential metabolites, including sterols, dolichols and ubiquinone. In Saccharomyces cerevisiae, FPPS catalyzes the sequential condensation of two molecules of isopentenyl diphosphate (IPP) with dimethylallyl diphosphate (DMAPP), producing geranyl diphosphate (GPP) and farnesyl diphosphate (FPP). Critical amino acid residues that determine product chain length were determined by a comparative study of strict GPP synthases versus strict FPPS. In silico ΔΔG, i.e. differential binding energy between a protein and two different ligands-of yeast FPPS mutants was evaluated, and F96, A99 and E165 residues were identified as key determinants for product selectivity. A99X variants were evaluated in vivo, S. cerevisiae strains carrying A99R and A99H variants showed significant differences on GPP concentrations and specific growth rates. The FPPS A99T variant produced unquantifiable amounts of FPP and no effect on GPP production was observed. Strains carrying A99Q, A99Y and A99K FPPS accumulated high amounts of DMAPP-IPP, with a decrease in GPP and FPP. Our results demonstrated the relevance of the first residue before FARM (First Aspartate Rich Motif) over substrate consumption and product specificity of S. cerevisiae FPPS in vivo. The presence of A99H significantly modified product selectivity and appeared to be relevant for GPP synthesis.

Endogenous sterol biosynthesis is important for mitochondrial function and cell morphology in procyclic forms of Trypanosoma brucei

Sterol biosynthesis inhibitors are promising entities for the treatment of trypanosomal diseases. Insect forms of Trypanosoma brucei, the causative agent of sleeping sickness, synthesize ergosterol and other 24-alkylated sterols, yet also incorporate cholesterol from the medium. While sterol function has been investigated by pharmacological manipulation of sterol biosynthesis, molecular mechanisms by which endogenous sterols influence cellular processes remain largely unknown in trypanosomes. Here we analyse by RNA interference, the effects of a perturbation of three specific steps of endogenous sterol biosynthesis in order to dissect the role of specific intermediates in proliferation, mitochondrial function and cellular morphology in procyclic cells. A decrease in the levels of squalene synthase and squalene epoxidase resulted in a depletion of cellular sterol intermediates and end products, impaired cell growth and led to aberrant morphologies, DNA fragmentation and a profound modification of mitochondrial structure and function. In contrast, cells deficient in sterol methyl transferase, the enzyme involved in 24-alkylation, exhibited a normal growth phenotype in spite of a complete abolition of the synthesis and content of 24-alkyl sterols. Thus, the data provided indicates that while the depletion of squalene and post-squalene endogenous sterol metabolites results in profound cellular defects, bulk 24-alkyl sterols are not strictly required to support growth in insect forms of T. brucei in vitro.

Farnesol production from Escherichia coli by harnessing the exogenous mevalonate pathway

Farnesol (FOH) production has been carried out in metabolically engineered Escherichia coli. FOH is formed through the depyrophosphorylation of farnesyl pyrophosphate (FPP), which is synthesized from isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP) by FPP synthase. In order to increase FPP synthesis, E. coli was metabolically engineered to overexpress ispA and to utilize the foreign mevalonate (MVA) pathway for the efficient synthesis of IPP and DMAPP. Two-phase culture using a decane overlay of the culture broth was applied to reduce volatile loss of FOH produced during culture and to extract FOH from the culture broth. A FOH production of 135.5 mg/L was obtained from the recombinant E. coli harboring the pTispA and pSNA plasmids for ispA overexpression and MVA pathway utilization, respectively. It is interesting to observe that a large amount of FOH could be produced from E. coli without FOH synthase by the augmentation of FPP synthesis. Introduction of the exogenous MVA pathway enabled the dramatic production of FOH by E. coli while no detectable FOH production was observed in the endogenous MEP pathway-only control.

Geranylgeranyl pyrophosphate is a potent regulator of HRD-dependent 3-Hydroxy-3-methylglutaryl-CoA reductase degradation in yeast

3-Hydroxy-3-methylglutaryl (HMG)-CoA reductase (HMGR), the rate-limiting enzymes of sterol synthesis, undergoes feedback-regulated endoplasmic reticulum degradation in both mammals and yeast. The yeast Hmg2p isozyme is subject to ubiquitin-mediated endoplasmic reticulum degradation by the HRD pathway. We had previously shown that alterations in cellular levels of the 15-carbon sterol pathway intermediate farnesyl pyrophosphate (FPP) cause increased Hmg2p ubiquitination and degradation. We now present evidence that the FPP-derived, 20-carbon molecule geranylgeranyl pyrophosphate (GGPP) is a potent endogenous regulator of Hmg2p degradation. This work was launched by the unexpected observation that GGPP addition directly to living yeast cultures caused high potency and specific stimulation of Hmg2p degradation. This effect of GGPP was not recapitulated by FPP, GGOH, or related isoprenoids. GGPP-caused Hmg2p degradation met all the criteria for the previously characterized endogenous signal. The action of added GGPP did not require production of endogenous sterol molecules, indicating that it did not act by causing the build-up of an endogenous pathway signal. Manipulation of endogenous GGPP by several means showed that naturally made GGPP controls Hmg2p stability. Analysis of the action of GGPP indicated that the molecule works upstream of retrotranslocation and can directly alter the structure of Hmg2p. We propose that GGPP is the FPP-derived regulator of Hmg2p ubiquitination. Intriguingly, the sterol-dependent degradation of mammalian HMGR is similarly stimulated by the addition of GGOH to intact cells, implying that a dependence on 20-carbon geranylgeranyl signals may be a common conserved feature of HMGR regulation that may lead to highly specific therapeutic approaches for modulation of HMGR.

Overproduction of geranylgeraniol by metabolically engineered Saccharomyces cerevisiae

(E, E, E)-Geranylgeraniol (GGOH) is a valuable starting material for perfumes and pharmaceutical products. In the yeast Saccharomyces cerevisiae, GGOH is synthesized from the end products of the mevalonate pathway through the sequential reactions of farnesyl diphosphate synthetase (encoded by the ERG20 gene), geranylgeranyl diphosphate synthase (the BTS1 gene), and some endogenous phosphatases. We demonstrated that overexpression of the diacylglycerol diphosphate phosphatase (DPP1) gene could promote GGOH production. We also found that overexpression of a BTS1-DPP1 fusion gene was more efficient for producing GGOH than coexpression of these genes separately. Overexpression of the hydroxymethylglutaryl-coenzyme A reductase (HMG1) gene, which encodes the major rate-limiting enzyme of the mevalonate pathway, resulted in overproduction of squalene (191.9 mg liter(-1)) rather than GGOH (0.2 mg liter(-1)) in test tube cultures. Coexpression of the BTS1-DPP1 fusion gene along with the HMG1 gene partially redirected the metabolic flux from squalene to GGOH. Additional expression of a BTS1-ERG20 fusion gene resulted in an almost complete shift of the flux to GGOH production (228.8 mg liter(-1) GGOH and 6.5 mg liter(-1) squalene). Finally, we constructed a diploid prototrophic strain coexpressing the HMG1, BTS1-DPP1, and BTS1-ERG20 genes from multicopy integration vectors. This strain attained 3.31 g liter(-1) GGOH production in a 10-liter jar fermentor with gradual feeding of a mixed glucose and ethanol solution. The use of bifunctional fusion genes such as the BTS1-DPP1 and ERG20-BTS1 genes that code sequential enzymes in the metabolic pathway was an effective method for metabolic engineering.