Engineering the lycopene synthetic pathway in <Emphasis Type="Italic">E. coli</Emphasis> by comparison of the carotenoid genes of <Emphasis Type="Italic">Pantoea agglomerans</Emphasis> and <Emphasis Type="Italic">Pantoea ananatis</Emphasis>

The lycopene synthetic pathway was engineered in Escherichia coli using the carotenoid genes (crtE, crtB, and crtI) of Pantoea agglomerans and Pantoea ananatis. E. coli harboring the P. agglomerans crt genes produced 27 mg/l of lycopene in 2YT medium without isopropyl-beta-d-thiogalactopyranoside (IPTG) induction, which was twofold higher than that produced by E. coli harboring the P. ananatis crt genes (12 mg/l lycopene) with 0.1 mM IPTG induction. The crt genes of P. agglomerans proved better for lycopene production in E. coli than those of P. ananatis. The crt genes of the two bacteria were also compared in E. coli harboring the mevalonate bottom pathway, which was capable of providing sufficient carotenoid building blocks, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), with exogenous mevalonate supplementation. Lycopene production significantly increased using the mevalonate bottom pathway and 60 mg/l of lycopene was obtained with the P. agglomerans crt genes, which was higher than that obtained with the P. ananatis crt genes (35 mg/l lycopene). When crtE among the P. ananatis crt genes was replaced with P. agglomerans crtE or Archaeoglobus fulgidus gps, both lycopene production and cell growth were similar to that obtained with P. agglomerans crt genes. The crtE gene was responsible for the observed difference in lycopene production and cell growth between E. coli harboring the crt genes of P. agglomerans and P. ananatis. As there was no significant difference in lycopene production between E. coli harboring P. agglomerans crtE and A. fulgidus gps, farnesyl diphosphate (FPP) synthesis was not rate-limiting in E. coli. Sang-Hwal Yoon and Ju-Eun Kim: These authors contributed equally to this work.     

Synthesis of carotenoids by<Emphasis Type="Italic"> Rhodotorula rubra</Emphasis> GED8 co-cultured with yogurt starter cultures in whey ultrafiltrate

Two cultures, a yeast (Rhodorula rubra GED8) and a yogurt starter (Lactobacillus bulgaricus 2–11+Streptococcus thermophilus 15HA), were selected for associated growth in whey ultrafiltrate (WU) and active synthesis of carotenoids. In associated cultivation with the yogurt culture L bulgaricus 2–11+S. thermophilus 15HA under intensive aeration (1.3 l^–1min^–1 air-flow rate) in WU (45 g lactose l^–1), initial pH 5.5, 30 °C, the lactose-negative strain R. rubra GED8 synthesized large amounts of carotenoids (13.09 mg l^–1 culture fluid). The carotenoid yield was approximately two-fold higher in association with a mixed yogurt culture than in association with pure yogurt bacteria. The major carotenoid pigments comprising the total carotenoids were -carotene (50%), torulene (12.3%) and torularhodin (35.2%). Carotenoids with a high -carotene content were produced by the microbial association 36 h earlier than by Rhodotorula yeast species. No significant differences were notd in the ratio between the pigments synthesized by R. rubra GED8+L. bulgaricus 2–11, R. rubra GED8+S. thermophilus 15HA, and R.rubra GED8+yogurt culture, despite the fact that the total carotenoid concentrations were lower in the mixed cultures with pure yogurt bacteria.     

Redesign,Reconstruction, and Directed Extension of the Brevibacterium linens C40 Carotenoid Pathway in Escherichia coli

In this study, the carotenoid biosynthetic pathways of Brevibacterium linens DSMZ 20426 were reconstructed, redesigned, and extended with additional carotenoid-modifying enzymes of other sources in a heterologous host Escherichia coli. The modular lycopene pathway synthesized an unexpected carotenoid structure, 3,4-didehydrolycopene, as well as lycopene. Extension of the novel 3,4-didehydrolycopene pathway with the mutant Pantoea lycopene cyclase CrtY₂ and the Rhodobacter spheroidene monooxygenase CrtA generated monocyclic torulene and acyclic oxocarotenoids, respectively. The reconstructed β-carotene pathway synthesized an unexpected 7,8-dihydro-β-carotene in addition to β-carotene. Extension of the β-carotene pathway with the B. linens β-ring desaturase CrtU and Pantoea β-carotene hydroxylase CrtZ generated asymmetric carotenoid agelaxanthin A, which had one aromatic ring at the one end of carotene backbone and one hydroxyl group at the other end, as well as aromatic carotenoid isorenieratene and dihydroxy carotenoid zeaxanthin. These results demonstrate that reconstruction of the biosynthetic pathways and extension with promiscuous enzymes in a heterologous host holds promise as a rational strategy for generating structurally diverse compounds that are hardly accessible in nature.Carotenoids, which are produced by many microorganisms and plants, belong to a class of pigment chemicals found in nature. These structurally diverse pigments have different biological functions such as coloration, photo protection, light-harvesting, and precursors for many hormones (3, 22). Carotenoids are commercially used as food colorants, animal feed supplements and, more recently, as nutraceuticals and as cosmetic and pharmaceutical compounds (19). Currently, only a few carotenoids can be produced commercially by chemical synthesis, fermentation, or isolation from a few abundant natural sources (13). The increasing industrial importance of carotenoids has led to renewed efforts to develop bioprocesses for large-scale production of a range of carotenoids, including lycopene, β-carotene, and more structurally diverse carotenoids (17, 21, 30, 31, 34). Interestingly, a recent study showed that carotenoids with more diverse structures tend to have higher biological activity than simple structures (1).Previously, in vitro evolution altered the catalytic functions of the carotenoid enzymes phytoene desaturase CrtI and lycopene cyclase CrtY (Fig. ​(Fig.1)1) and produced novel carotenoid structures of tetradehydrolycopene and torulene in Escherichia coli (27). Furthermore, these in vitro evolved pathways and redesigned C₃₀ carotenoid biosynthetic pathways were successfully extended with additional, wild-type carotenoid modifying enzymes and evolved enzymes (21), generating novel carotenoid structures (26).Open in a separate windowFIG. 1.Reconstructed and redesigned B. linens carotenoid biosynthetic pathway in the heterologous host E. coli. Carotenogenic enzymes of B. linens, P. ananatis, and R. capsulatus, which were used for the biosynthetic pathway reconstruction, are indicated by boldface letters. Idi (IPP isomerase), IspA (FPP synthase), CrtE (GGPP synthase), CrtB (phytoene synthase), CrtI (phytoene desaturase), CrtYcYd (lycopene cyclase), CrtU (β-carotene desaturase), CrtZ (β-carotene hydrolase), CrtY₂ (mutant lycopene cyclase), and CrtA (spheroidene monooxygenase). B. linens 3,3′-dihydroxyisorenieratene biosynthesis is indicated by dashed arrows.Beside in vitro evolution (23, 34), combinatorial biosynthesis with carotenoid-modifying enzymes in a heterologous host has often been used to generate structurally novel carotenoids (24, 32). This combinatorial biosynthetic approach basically relies on the functional coordination of pathway enzymes from different sources in a heterologous host (5, 19, 35). Carotenogenic enzymes tend to be promiscuous in their substrate specificity (33) and show unexpected/hidden activities (20) when expressed in heterologous host microorganisms. One example is the unusual activity of diapophytoene desaturase CrtN in E. coli, which resulted in structurally novel compounds (20). Therefore, utilizing the promiscuity of carotenogenic enzymes makes combinatorial biosynthesis one of the most powerful strategies to generate structurally novel carotenoids that cannot be accessed in nature.Yellow colored Brevibacterium linens is commonly used as a food colorant by the cheese industry (15). Interestingly, B. linens is known to synthesize aromatic ring-containing carotenoids, isorenieratene and its hydroxy derivatives (6, 7, 16). They are produced by seven carotenogenic enzymes expressed in B. linens: GGPP synthase CrtE, phytoene synthase CrtE, phytoene desaturase CrtI, lycopene cyclase CrtYcYd, β-carotene desaturase CrtU, and the cytochrome P450 (Fig. ​(Fig.1).1). Even though the carotenoid biosynthetic pathways of B. linens have been recently studied (6, 10), there have been no systematic functional study of downstream enzymes such as lycopene cyclase CrtYcYd in the biosynthetic pathway of B. linens in a heterologous environment.Therefore, in the present study, for the first time we reconstructed, redesigned, and rationally extended the B. linens carotenoids biosynthetic pathway in E. coli to investigate the flexibility of the pathway enzymes in a heterologous host. Using this approach, we obtained an unexpected structure 3,4-didehydrolycopene, 7,8-dihydro-β-carotene, torulene, and the asymmetric carotenoid, agelaxanthin A, from engineered B. linens carotenoid pathways in E. coli.     

Purification and characterization of the fusion protein trypsin-streptavidin expressed in Escherichia coli

Expression of fusion protein trypsin-streptavidin (TRYPSA)⁴ in Escherichia coli was evaluated and the protein purified. Protein expression was induced by 1 mM isopropylthio--D-galactoside (IPTG), and the enzyme activity was measured by the hydrolysis rate of p-toluenesulfonyl-l-arginine methyl ester (TAME). Expression of the fusion protein in the cell-free extract decreased with increased induction time; correspondingly, that in the inclusion bodies increased. The total expression in Luria–Bertani broth (LB) and Terrific Broth (TB) media reached the highest levels in 2 hr at 30°C. The optimum expression level was 35 and 48 U/L in LB and TB, respectively. Expression of the fusion protein was verified by Western Blot analysis using streptavidin antiserum, and the fusion protein was purified using a benzamidine Sepharose 6B affinity column at room temperature. The molecular size of the soluble purified fusion protein was determined by size-exclusion chromatography using Superose 12 FPLC. A molecular weight of 39–40 kDa was obtained, indicating that the soluble protein exists as a monomer; thus, the presence of the trypsin domain must prevent the streptavidin domain from tetramer formation.     

Increase of lycopene production by supplementing auxiliary carbon sources in metabolically engineered <Emphasis Type="Italic">Escherichia coli</Emphasis>

In the fed-batch culture of glycerol using a metabolically engineered strain of Escherichia coli, supplementation with glucose as an auxiliary carbon source increased lycopene production due to a significant increase in cell mass, despite a reduction in specific lycopene content. l-Arabinose supplementation increased lycopene production due to increases in cell mass and specific lycopene content. Supplementation with both glucose and l-arabinose increased lycopene production significantly due to the synergistic effect of the two sugars. Cell growth by the consumption of carbon sources was related to endogenous metabolism in the host E. coli. Supplementation with l-arabinose stimulated only the mevalonate pathway for lycopene biosynthesis and supplementation with both glucose and l-arabinose stimulated synergistically only the mevalonate pathway. In the fed-batch culture of glycerol with 10 g l⁻¹ glucose and 7.5 g l⁻¹ l-arabinose, the cell mass, lycopene concentration, specific lycopene content, and lycopene productivity after 34 h were 42 g l⁻¹, 1,350 mg l⁻¹, 32 mg g cells⁻¹, and 40 mg l⁻¹ h⁻¹, respectively. These values were 3.9-, 7.1-, 1.9-, and 11.7-fold higher than those without the auxiliary carbon sources, respectively. This is the highest reported concentration and productivity of lycopene.     

Production of vanillin from ferulic acid using recombinant strains ofEscherichia coli

Vanillin is one of the world's principal flavoring compounds, and is used extensively in the food industry. The potential vanillin production of the bacteria was compared to select and clone genes which were appropriate for highly productive vanillin production byE. coli. Thefcs (feruloyl-CoA synthetase) andech (enoyl-CoA hydratase/aldolase) genes cloned fromAmycolatopsis sp. strain HR104 andDelftia acidovorans were introduced to pBAD24 vector with P_BAD promoter and were named pDAHEF and pDDAEF, respectively. We observed 160 mg/L vanillin production withE. coli harboring pDAHEF, whereas 10 mg/L of vanillin was observed with pDDAEF. Vanillin production was optimized withE. coli harboring pDAHEF. Induction of thefcs andech genes from pDAHEF was optimized with the addition of 13.3 mM arabinose at 18 h of culture, from which 450 mg/L of vanillin was produced. The feeding time and concentration of ferulic acid were also optimized by the supplementation of 0.2% ferulic acid at 18 h of culture, from which 500 mg/L of vanillin was obtained. Under the above optimized condition of arabinose induction and ferulic acid supplementation, vanillin production was carried out with four different types of media, M9, LB, 2YT, and TB. The highest vanillin production, 580 mg/L, was obtained with LB medium, a 3.6 fold increase in comparison to the 160 mg/L obtained before the optimization of vanillin production.     

Growth conditions required for bacteriocin production by strains of <Emphasis Type="Italic">Staphylococcus aureus</Emphasis>

The influence of growth parameters on the production of bacteriocins (aureocins) by five strains of Staphylococcus aureus was investigated. These aureocins have a broad spectrum of activity and can inhibit important human and animal pathogens. All strains produced large inhibition zones upon the indicator strain when they were grown in rich media such as brain-heart infusion (BHI), N2GT and 2 × YT. Bacteriocin production was not influenced by the initial pH of the medium (6.0–8.0). At lower temperature (28 °C), there was a marked reduction in bacteriocin production. Incubation of the producers under anaerobiosis affected profoundly the production of two related bacteriocins, aureocins MB92 and 146L, and slightly increased the production of aureocins A53 and 215FN. Production of aureocins MB92 and 215FN was apparently abolished in media containing 2.5 g and 3.5 g Nacl/100 ml, respectively. Although production of the remaining aureocins was observed in all NaCl concentrations tested (0.5–7.5 g/100 ml), the larger inhibition zones were detected in media containing up to either 1.5 g (for aureocins A70 and 146L) or 2.5 g NaCl/100 ml (for aureocin A53). Aureocin 215FN could not be detected in the culture supernatant. For the remaining aureocins tested, the highest levels of bacteriocin production occurred in either the late-log or early stationary growth phase of cultures grown in BHI medium at 37 °C. Changes in environmental conditions can, therefore, have detrimental effects on the production of active aureocins. Such factors are relevant when considering the potential biotechnological applications of these substances and when testing new S. aureus isolates for bacteriocin production.     

Identification of the gene responsible for torulene cleavage in the Neurospora carotenoid pathway

Torulene, a C₄₀ carotene, is the precursor of the end product of the Neurospora carotenoid pathway, the C₃₅ xanthophyll neurosporaxanthin. Torulene is synthesized by the enzymes AL-2 and AL-1 from the precursor geranylgeranyl diphosphate and then cleaved by an unknown enzyme into the C₃₅ apocarotenoid. In general, carotenoid cleavage reactions are catalyzed by carotenoid oxygenases. Using protein data bases, we identified two putative carotenoid oxygenases in Neurospora, named here CAO-1 and CAO-2. A search for novel mutants of the carotenoid pathway in this fungus allowed the identification of two torulene-accumulating strains, lacking neurosporaxanthin. Sequencing of the cao-2 gene in these strains revealed severe mutations, pointing to a role of CAO-2 in torulene cleavage. This was further supported by the identical phenotype found upon targeted disruption of cao-2. The biological function was confirmed by in vitro assays using the purified enzyme, which cleaved torulene to produce β-apo-4′-carotenal, the corresponding aldehyde of neurosporaxanthin. The specificity of CAO-2 was shown by the lack of γ-carotene-cleaving activity in vitro. As predicted for a structural gene of the carotenoid pathway, cao-2 mRNA was induced by light in a WC-1 and WC-2 dependent manner. Our data demonstrate that CAO-2 is the enzyme responsible for the oxidative cleavage of torulene in the neurosporaxanthin biosynthetic pathway.     

Biosynthesis of aryl carotenoids: Inhibitor studies of chlorobactene biosynthesis in Chlorobium limicola f. thiosulfatophilum

The biosynthesis of the aryl carotenoid, chlorobactene, was examined in the green sulfur bacterium, Chlorobium limicola f. thiosulfatophilum. Nicotine, which was used to inhibit carotenoid cyclization, caused the accumulation of the acyclic carotenoid, lycopene. Cells reincubated in fresh medium, after removal of nicotine, synthesized chlorobactene more readily from newly synthesized lycopene rather than from the pool of lycopene accumulated during nicotine inhibition. When the cells were reincubated in the presence of diphenylamine, which inhibited de novo carotenogenesis, a portion of the lycopene which had accumulated during nicotine inhibition was converted into chlorobactene. There was no evidence that neurosporene, rather than lycopene, was the precyclization intermediate. The involvement of -carotene as the cyclic precursor of chlorobactene also was shown. The pathway for chlorobactene biosynthesis is discussed in terms of a possible arrangement of the enzymes involved in carotenoid biosynthesis.Abbreviations DPA Diphenylamine - TLC Thin layer chromatography     

Molecular cloning and expression of the pyranose 2-oxidase cDNA from<Emphasis Type="Italic"> Trametes ochracea</Emphasis> MB49 in<Emphasis Type="Italic"> Escherichia coli</Emphasis>

A cDNA of a structural gene encoding pyranose 2-oxidase (P2O) from Trametes ochracea strain MB49 was cloned into Escherichia coli strain BL21(DE3) on a multicopy plasmid under the control of the trc promoter. Synthesis of P2O was studied in batch cultures in LB or M9-based mineral medium at 28°C. While there was a low specific activity of P2O in LB medium, the enzyme was synthesised constitutively in mineral medium and represented 3% of the cell soluble protein (0.3 U mg^–1). The effect of isopropyl -d-thiogalactoside on the expression of P2O was studied in mineral medium at 25 and 28°C. The synthesis of P2O at 28°C corresponded to 39% of the cell soluble protein but the major portion of P2O (93%) was in the form of non-active inclusion bodies (activity of P2O equalled 0.19 U mg^–1). At 25°C, the amount of P2O represented 14% of the cell soluble protein and the activity of P2O was 1.1 U mg^–1. The soluble enzyme represented 70% of the total amount of P2O.     

The neutral carotenoids of wild-type and mutant strains of Neurospora crassa

The neutral carotenoids of wild-type Neurospora crassa and of carotenoid mutants at four discrete genetic loci were isolated using gradient elution chromatography on deactivated alumina columns. Carotenoids were identified by absorption spectrophotometry and thin layer cochromatography with carotenoid standards. Phytoene, phytofluene, -carotene, -carotene, neurosporene, torulene, lycopene, and 3,4-dehydrolycopene were isolated from wild type. Phytoene, phytofluene, -carotene, -carotene, neurosporene, -carotene, lycopene, and one unknown carotenoid, tentatively identified as 15,15-cis--carotene, were isolated from a yellow mutant, ylo-1. ylo-1 also contained residual carotenoids having similar absorption spectra to, but very different chromatographic behavior from, phytofluene, -carotene, -carotene, and lycopene. Albino and colored al-1 mutants contained large amounts of phytoene and only traces of other neutral carotenoids. Albino al-2 and al-3 mutants contained only traces of neutral carotenoids.     

A carotenoid synthesis gene cluster from Algoriphagus sp. KK10202C with a novel fusion-type lycopene β-cyclase gene

A carotenoid synthesis gene cluster was isolated from a marine bacterium Algoriphagus sp. strain KK10202C that synthesized flexixanthin. Seven genes were transcribed in the same direction, among which five of them were involved in carotenoid synthesis. This cluster had a unique gene organization, with an isoprenoid gene, ispH (previously named lytB), being present among the carotenoid synthesis genes. The lycopene β-cyclase encoded by the crtY _cd gene appeared to be a fusion of bacterial heterodimeric lycopene cyclase CrtY_c and CrtY_d. This was the first time that a fusion-type of lycopene β-cyclase was reported in eubacteria. Heterologous expression of the Algoriphagus crtY _cd gene in lycopene-accumulating Escherichia coli produced bicyclic β-carotene. A biosynthesis pathway for monocyclic flexixanthin was proposed in Algoriphagus sp. strain KK10202C, though several of the carotenoid synthesis genes not linked with the cluster have not yet been cloned.     

Biosynthetic Pathway for γ-Cyclic Sarcinaxanthin in Micrococcus luteus: Heterologous Expression and Evidence for Diverse and Multiple Catalytic Functions of C50 Carotenoid Cyclases

We report the cloning and characterization of the biosynthetic gene cluster (crtE, crtB, crtI, crtE2, crtYg, crtYh, and crtX) of the γ-cyclic C₅₀ carotenoid sarcinaxanthin in Micrococcus luteus NCTC2665. Expression of the complete and partial gene cluster in Escherichia coli hosts revealed that sarcinaxanthin biosynthesis from the precursor molecule farnesyl pyrophosphate (FPP) proceeds via C₄₀ lycopene, C₄₅ nonaflavuxanthin, C₅₀ flavuxanthin, and C₅₀ sarcinaxanthin. Glucosylation of sarcinaxanthin was accomplished by the crtX gene product. This is the first report describing the biosynthetic pathway of a γ-cyclic C₅₀ carotenoid. Expression of the corresponding genes from the marine M. luteus isolate Otnes7 in a lycopene-producing E. coli host resulted in the production of up to 2.5 mg/g cell dry weight sarcinaxanthin in shake flasks. In an attempt to experimentally understand the specific difference between the biosynthetic pathways of sarcinaxanthin and the structurally related ɛ-cyclic decaprenoxanthin, we constructed a hybrid gene cluster with the γ-cyclic C₅₀ carotenoid cyclase genes crtYg and crtYh from M. luteus replaced with the analogous ɛ-cyclic C₅₀ carotenoid cyclase genes crtYe and crtYf from the natural decaprenoxanthin producer Corynebacterium glutamicum. Surprisingly, expression of this hybrid gene cluster in an E. coli host resulted in accumulation of not only decaprenoxanthin, but also sarcinaxanthin and the asymmetric ɛ- and γ-cyclic C₅₀ carotenoid sarprenoxanthin, described for the first time in this work. Together, these data contributed to new insight into the diverse and multiple functions of bacterial C₅₀ carotenoid cyclases as key catalysts for the synthesis of structurally different carotenoids.Carotenoids are natural pigments synthesized by bacteria, fungi, algae, and plants, and more than 750 different carotenoids have been isolated from natural sources (17). They possess important biological functions as protectants against light and oxygen excess in photosynthetic processes (32, 38), and they have been proposed to reduce the risk of certain cancers, cardiovascular disease, and Alzheimer disease due to their antioxidative properties (20, 46). The global market for carotenoids used as food colorants and nutritional supplements was estimated at approximately $935 million in 2005 (11). More than 95% of all natural carotenoids are based on a symmetric C₄₀ phytoene backbone, and only a small number of C₃₀ and even fewer C₅₀ carotenoids have been discovered (42).C₅₀ carotenoids have multiple conjugated double bonds, and they contain at least one hydroxyl group; both these features contribute to strong antioxidative properties (17, 30, 32, 38). In nature, C₅₀ carotenoids are synthesized by bacteria of the order Actinomycetales, and to date, only two different C₅₀ carotenoid biosynthetic pathways have been described in the literature. The biosynthetic pathways of the ɛ-cyclic C₅₀ carotenoid decaprenoxanthin [2,2′-bis-(4-hydroxy-3-methybut-2-enyl)-ɛ,ɛ-carotene] and the β-cyclic C₅₀ carotenoid C.p.450 [2,2′-bis-(4-hydroxy-3-methybut-2-enyl)-β,β-carotene] have been elucidated in Corynebacterium glutamicum (22, 23) and in Dietzia sp. CQ4 (41), respectively. For both pathways, the common precursor, C₄₀ lycopene, is synthesized from C₁₅ farnesyl pyrophosphate (FPP) via the methylerythritol 4-phosphate (MEP) pathway, which is present in most eubacteria (33). Effective lycopene production has been achieved in genetically engineered noncarotenogenic hosts, such as Escherichia coli and Saccharomyces cerevisiae (9). Accordingly, the potential of using such biotechnologically relevant hosts for heterologous production of any lycopene-derived carotenoids has generated high interest.The biosynthesis of cyclic C₅₀ carotenoids from lycopene is catalyzed by lycopene elongase and carotenoid cyclases. Even though most carotenoids in plants and microorganisms exhibit cyclic structures, cyclization reactions were predominantly known for C₄₀ pathways (45) catalyzed by monomeric enzymes that have been isolated from plants and bacteria (5, 16, 27, 29, 31, 36). In C. glutamicum, the genes crtYe, crtYf, and crtEb were identified as being involved in the conversion of lycopene to the ɛ-cyclic C₅₀ carotenoid decaprenoxanthin (22, 44). Sequential elongation of lycopene into the acyclic C₅₀ carotenoid flavuxanthin was catalyzed by the crtEb gene product lycopene elongase. Subsequent cyclization to decaprenoxanthin was catalyzed by a heterodimeric C₅₀ carotenoid, ɛ-cyclase, encoded by crtYe and crtYf (22). C. glutamicum can synthesize both mono- and diglucosylated decaprenoxanthin; however, the genetic and enzymatic bases for glucosylation of decaprenoxanthin are unknown. Analogous to decaprenoxanthin, biosynthesis of the β-cyclic C₅₀ carotenoid C.p.450 in Dietzia sp. CQ4 from lycopene involves lycopene elongase and C₅₀ carotenoid β-cyclase activities (41).While most cyclic carotenoids exhibit β-rings, ɛ-ring-containing pigments are common in higher plants (7), and carotenoids substituted only with γ-rings are rarely observed in plants and algae (14). To date, no biosynthetic pathway for γ-cyclic C₅₀ carotenoids has been reported in the literature.Micrococcus luteus NCTC2665 (the “Fleming strain”) is a Gram-positive bacterium belonging to the family Micrococcaceae within the order Actinomycetales. The carotenoids, including the γ-cyclic C₅₀ sarcinaxanthin [(2R,6R,2′R,6′R)-(2,2′-bis(4-hydroxy-3-methyl-2-butenyl)-γ,γ-carotene)], synthesized by this bacterium have been identified and structurally elucidated (26). We recently isolated and characterized several wild-type M. luteus strains from the sea surface microlayer of the middle part of the Norwegian coast (39). Here, we report one additional such marine M. luteus isolate, designated Otnes7, forming color-intensive colonies indicating high sarcinaxanthin production levels. Both Otnes7 and NCTC2665 were used as M. luteus model strains, and the sarcinaxanthin biosynthetic gene clusters were cloned from both strains. The complete sarcinaxanthin biosynthetic pathway from lycopene was elucidated, including glucosylation, and we also explored the potential of using Otnes7-derived genes to achieve effective heterologous production of sarcinaxanthin in E. coli. The results add important new knowledge of the biosynthesis of C₅₀ carotenoids, and in particular, they highlight the diverse functions of C₅₀ carotenoid cyclases leading to synthesis of structurally different carotenoids.     

Effect of anaerobic promoters on the microaerobic production of polyhydroxybutyrate (PHB) in recombinant <Emphasis Type="Italic">Escherichia coli</Emphasis>

Nine anaerobic promoters were cloned and constructed upstream of PHB synthesis genes phbCAB from Ralstonia eutropha for the micro- or anaerobic PHB production in recombinant Escherichia coli. Among the promoters, the one for alcohol dehydrogenase (P _adhE ) was found most effective. Recombinant E. coli JM 109 (pWCY09) harboring P _adhE and phbCAB achieved a 48% PHB accumulation in the cell dry weight after 48 h of static culture compared with only 30% PHB production under its native promoter. Sixty-seven percent PHB was produced in the dry weight (CDW) of an acetate pathway deleted (Δpta deletion) E. coli JW2294 harboring the vector pWCY09. In a batch process conducted in a 5.5-l NBS fermentor containing 3 l glucose LB medium, E. coli JW2294 (pWCY09) grew to 7.8 g/l CDW containing 64% PHB after 24 h of microaerobic incubation. In addition, molecular weight of PHB was observed to be much higher under microaerobic culture conditions. The high activity of P _adhE appeared to be the reason for improved micro- or anaerobic cell growth and PHB production while high molecular weight contributed to the static culture condition.     

Metabolic Engineering for Production of β-Carotene and Lycopene in Saccharomyces cerevisiae

We have engineered a conventional yeast, Saccharomyces cerevisiae, to confer a novel biosynthetic pathway for the production of β-carotene and lycopene by introducing the bacterial carotenoid biosynthesis genes, which are individually surrounded by the promoters and terminators derived from S. cerevisiae. β-Carotene and lycopene accumulated in the cells of this yeast, which was considered to be a result of the carbon flow for the ergosterol biosynthetic pathway being partially directed to the pathway for the carotenoid production.     

Efficient synthesis of functional isoprenoids from acetoacetate through metabolic pathway-engineered <Emphasis Type="Italic">Escherichia coli</Emphasis>

We show here an efficient synthesis system of isoprenoids from acetoacetate as the main substrate. We expressed in Escherichia coli a Streptomyces mevalonate pathway gene cluster starting from HMG-CoA synthase and including isopentenyl diphosphate isomerase (idi) type 2 gene and the yeast idi type 1 and rat acetoacetate-CoA ligase (Aacl) genes. When the α-humulene synthase (ZSS1) gene of shampoo ginger was expressed in this transformant, the resultant E. coli produced 958 μg/mL culture of α-humulene with a lithium acetoacetate (LAA) supplement, which was a 13.6-fold increase compared with a control E. coli strain expressing only ZSS1. Next, we investigated if this E. coli strain engineered to utilize acetoacetate can synthesize carotenoids effectively. When the crtE, crtB, and crtI genes required for lycopene synthesis were expressed in the transformant, lycopene amounts reached 12.5 mg/g dry cell weight with addition of LAA, an 11.8-fold increase compared with a control expressing only the three crt genes. As for astaxanthin production with the E. coli transformant, in which the crtE, crtB, crtI, crtY, crtZ, and crtW genes were expressed, the total amount of carotenoids produced (astaxanthin, lycopene, and phytoene) was significantly increased to 7.5 times that of a control expressing only the six crt genes.     

Production of l-alanine from ammonium fumarate using two immobilized microorganisms

Summary For the efficient production of l-alanine from ammonium fumarate using the aspartase activity of immobilized Escherichia coli cells and l-aspartate -decarboxylase activity of immobilized Pseudomonas dacunhae cells, alanine racemase and fumarase activities should be eliminated. We investigated various procedures to eliminate these side reactions, and found that both activities of intact E. coli cells could be eliminated by treating the culture broth at pH 5.0 and 45° C for 1 h, and those of intact P. dacunhae cells could be eliminated by treating the culture broth at pH 4.75 and 30° C for 1 h. Further, it was confirmed that l-alanine was efficiently produced using these two immobilized pH-treated microorganisms.     

High-Level Production of the Industrial Product Lycopene by the Photosynthetic Bacterium Rhodospirillum rubrum

The biosynthesis of the major carotenoid spirilloxanthin by the purple nonsulfur bacterium Rhodospirillum rubrum is thought to occur via a linear pathway proceeding through phytoene and, later, lycopene as intermediates. This assumption is based solely on early chemical evidence (B. H. Davies, Biochem. J. 116:93–99, 1970). In most purple bacteria, the desaturation of phytoene, catalyzed by the enzyme phytoene desaturase (CrtI), leads to neurosporene, involving only three dehydrogenation steps and not four as in the case of lycopene. We show here that the chromosomal insertion of a kanamycin resistance cassette into the crtC-crtD region of the partial carotenoid gene cluster, whose gene products are responsible for the downstream processing of lycopene, leads to the accumulation of the latter as the major carotenoid. We provide spectroscopic and biochemical evidence that in vivo, lycopene is incorporated into the light-harvesting complex 1 as efficiently as the methoxylated carotenoids spirilloxanthin (in the wild type) and 3,4,3′,4′-tetrahydrospirilloxanthin (in a crtD mutant), both under semiaerobic, chemoheterotrophic, and photosynthetic, anaerobic conditions. Quantitative growth experiments conducted in dark, semiaerobic conditions, using a growth medium for high cell density and high intracellular membrane levels, which are suitable for the conventional industrial production in the absence of light, yielded lycopene at up to 2 mg/g (dry weight) of cells or up to 15 mg/liter of culture. These values are comparable to those of many previously described Escherichia coli strains engineered for lycopene production. This study provides the first genetic proof that the R. rubrum CrtI produces lycopene exclusively as an end product.