R&D Biology, Antibióticos S.A., Avenida de Antibióticos 59-61, 24009 León, Spain.
Astaxanthin is a red xanthophyll (oxygenated carotenoid) with large importance in the aquaculture, pharmaceutical, and food industries. The green alga Haematococcus pluvialis and the heterobasidiomycetous yeast Xanthophyllomyces dendrorhous are currently known as the main microorganisms useful for astaxanthin production at the industrial scale. The improvement of astaxanthin titer by microbial fermentation is a requirement to be competitive with the synthetic manufacture by chemical procedures, which at present is the major source in the market. In this review, we show how the isolation of new strains of X. dendrorhous from the environment, the selection of mutants by the classical methods of random mutation and screening, and the rational metabolic engineering, have provided improved strains with higher astaxanthin productivity. To reduce production costs and enhance competitiveness from an industrial point of view, low-cost raw materials from industrial and agricultural origin have been adopted to get the maximal astaxanthin productivity. Finally, fermentation parameters have been studied in depth, both at flask and fermenter scales, to get maximal astaxanthin titers of 4.7 mg/g dry cell matter (420 mg/l) when X. dendrorhous was fermented under continuous white light. The industrial scale-up of this biotechnological process will provide a cost-effective method, alternative to synthetic astaxanthin, for the commercial exploitation of the expensive astaxanthin (about $2,500 per kilogram of pure astaxanthin).
Engineering of a plasmid-free Escherichia coli strain for improved in vivo biosynthesis of astaxanthin.
Institute of Microbiology, Universität Stuttgart, Stuttgart, Germany.
The xanthophyll astaxanthin is a high-value compound with applications in the nutraceutical, cosmetic, food, and animal feed industries. Besides chemical synthesis and extraction from naturally producing organisms like Haematococcus pluvialis, heterologous biosynthesis in non-carotenogenic microorganisms like Escherichia coli, is a promising alternative for sustainable production of natural astaxanthin. Recent achievements in the metabolic engineering of E. coli strains have led to a significant increase in the productivity of carotenoids like lycopene or β-carotene by increasing the metabolic flux towards the isoprenoid precursors. For the heterologous biosynthesis of astaxanthin in E. coli, however, the conversion of β-carotene to astaxanthin is obviously the most critical step towards an efficient biosynthesis of astaxanthin. Here we report the construction of the first plasmid-free E. coli strain that produces astaxanthin as the sole carotenoid compound with a yield of 1.4 mg/g cdw (E. coli BW-ASTA). This engineered E. coli strain harbors xanthophyll biosynthetic genes from Pantoea ananatis and Nostoc punctiforme as individual expression cassettes on the chromosome and is based on a β-carotene-producing strain (E. coli BW-CARO) recently developed in our lab. E. coli BW-CARO has an enhanced biosynthesis of the isoprenoid precursor isopentenyl diphosphate (IPP) and produces β-carotene in a concentration of 6.2 mg/g cdw. The expression of crtEBIY along with the β-carotene-ketolase gene crtW148 (NpF4798) and the β-carotene-hydroxylase gene (crtZ) under controlled expression conditions in E. coli BW-ASTA directed the pathway exclusively towards the desired product astaxanthin (1.4 mg/g cdw). By using the λ-Red recombineering technique, genes encoding for the astaxanthin biosynthesis pathway were stably integrated into the chromosome of E. coli. The expression levels of chromosomal integrated recombinant biosynthetic genes were varied and adjusted to improve the ratios of carotenoids produced by this E. coli strain. The strategy presented, which combines chromosomal integration of biosynthetic genes with the possibility of adjusting expression by using different promoters, might be useful as a general approach for the construction of stable heterologous production strains synthesizing natural products. This is the case especially for heterologous pathways where excessive protein overexpression is a hindrance.
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High-titer production of astaxanthin by the semi-industrial fermentation of Xanthophyllomyces dendrorhous.
Juan Luis de la Fuente, Marta Rodríguez-Sáiz, Carmen Schleissner, Bruno Díez, Enrique Peiro, José Luis Barredo
R&D Biology, Antibióticos S.A., Avenida de Antibióticos 59-61, 24009 León, Spain.
An improved semi-industrial process for astaxanthin production by fermentation of Xanthophyllomyces dendrorhous has been developed. The culture medium was designed at the flask scale, reaching an astaxanthin cellular content of 3.0 mgg(-1) cell weight and a volumetric yield of 119 mgL(-1) broth. Astaxanthin production in flask was significantly improved by white light (4.0 mgg(-1) and 221 mgL(-1)), and by ultraviolet light (4.4 mgg(-1) and 235 mgL(-1)). The scale-up to 10- and 800-L fermentors was developed by feeding with glucose. Representative data for illuminated fermentation processes are presented and discussed at the 10-L scale, where 420 mgL(-1)(4.7 mgg(-1)) astaxanthin were produced, and the 800-L scale, with productivities of 350 mgL(-1)(4.1 mgg(-1)) astaxanthin. The purity of the astaxanthin in the broth was about 84%, with accumulation of the following carotenoids other than astaxanthin: 4% beta-carotene, 4% canthaxanthin, 5% HDCO, 1% zeaxanthin and 2% phoenicoxanthin. This technology can be easily scaled-up to an industrial application for the production of this xanthophyll widely demanded nowadays.
The crtS gene of Xanthophyllomyces dendrorhous encodes a novel cytochrome-P450 hydroxylase involved in the conversion of beta-carotene into astaxanthin and other xanthophylls.
Vanessa Alvarez, Marta Rodríguez-Sáiz, Juan Luis de la Fuente, Eduardo J Gudiña, Ramiro P Godio, Juan F Martín, José Luis Barredo
R&D Biology, Antibióticos S.A., Avenida de Antibióticos 59-61, 24009 León, Spain.
The conversion of beta-carotene into xanthophylls is a subject of great scientific and industrial interest. We cloned the crtS gene involved in astaxanthin biosynthesis from two astaxanthin producing strains of Xanthophyllomyces dendrorhous: VKPM Y2410, an astaxanthin overproducing strain, and the wild type ATCC 24203. In both cases, the ORF has a length of 3166bp, including 17 introns, and codes for a protein of 62.6kDa with similarity to cytochrome-P450 hydroxylases. crtS gene sequences from strains VKPM Y2410, ATCC 24203, ATCC 96594, and ATCC 96815 show several nucleotide changes, but none of them causes any amino acid substitution, except a G(2268) insertion in the 13th exon of ATCC 96815 which causes a change in the reading frame. A G(1470)-->A change in the 5' splicing region of intron 8 was also found in ATCC 96815. Both point mutations explain astaxanthin idiotrophy and beta-carotene accumulation in ATCC 96815. Mutants accumulating precursors of the astaxanthin biosynthetic pathway were selected from the parental strain VKPM Y2410 (red) showing different colors depending on the compound accumulated. Two of them were blocked in the biosynthesis of astaxanthin, M6 (orange; 1% astaxanthin, 71 times more beta-carotene) and M7 (orange; 1% astaxanthin, 58 times more beta-carotene, 135% canthaxanthin), whereas the rest produced lower levels of astaxanthin (5-66%) than the parental strain. When the crtS gene was expressed in M7, canthaxanthin accumulation disappeared and astaxanthin production was partially restored. Moreover, astaxanthin biosynthesis was restored when X. dendrorhous ATCC 96815 was transformed with the crtS gene. The crtS gene was heterologously expressed in Mucor circinelloides conferring to this fungus an improved capacity to synthesize beta-cryptoxanthin and zeaxanthin, two hydroxylated compounds from beta-carotene. These results show that the crtS gene is involved in the conversion of beta-carotene into xanthophylls, being potentially useful to engineer carotenoid pathways.
R&D Biology, Antibióticos S.A., Avenida de Antibióticos 59-61, 24009 León, Spain.
We determined the nucleotide sequence of a 4599-bp DNA genomic fragment including the gamma-actin encoding gene from Blakeslea trispora, showing an open reading frame of 1561 bp interrupted by four introns with fungal consensus splice-site junctions. The untranslated regions of the actA gene contain a consensus TATA box, a CCAAT motif, a large pyrimidine stretch, and the polyadenylation sequence AATAAA. The predicted protein (375 amino acids) revealed high identity to gamma-actins from fungi (>90%), and gene phylogenies support the grouping of B. trispora actin close to those from the majority of the filamentous fungi. actA transcript (1.4 kb) level in beta-carotene producing conditions was faintly higher than carRA (1.9 kb) and slightly lower than carB (1.8 kb) beta-carotene biosynthetic genes. The use of the actA promoter (PactA) for heterologous gene expression was ascertained by the transformation of gene fusions with the bleomycin resistance gene (bleR) from Streptoalloteichus hindustanus and the geneticin resistance marker (aphI) from Tn903, into Escherichia coli and Acremonium chrysogenum.
R&D Biology, Antibióticos S.A., Avenida de Antibióticos 59-61, 24009 León, Spain.
We purified the beta-N-acetylglucosaminidase from the filamentous fungus Penicillium chrysogenum and its N-terminal sequence was determined, showing the presence of a mixture of two proteins (P1 and P2). A genomic DNA fragment was cloned by using degenerated oligonucleotides from the Nt sequences. The nucleotide sequence showed the presence of an ORF (nagA gene) lacking introns, with a length of 1791 bp, and coding for a protein of 66.5 kDa showing similarity to acetylglucosaminidases. The NagA deduced protein includes P1 and P2 as incomplete forms of the mature protein, and contains putative features for protein maturation: an 18-amino acid signal peptide, a KEX2 processing site, and four glycosylation motifs. The sequence just after the signal peptide corresponds to P2 and that after the KEX2 site to P1. The nagA transcript has a size of about 2.1 kb and is present until the end of the fermentation process for penicillin production. NagA is one of the most largely represented proteins in P. chrysogenum, increasing along the fermentation process. The suitability of the nagA promoter (PnagA) for gene expression in fungi was demonstrated by expressing the bleomycin resistance gene (ble(R)) from Streptoalloteichus hindustanus in P. chrysogenum.
Strain improvement for cephalosporin production by Acremonium chrysogenum using geneticin as a suitable transformation marker.
Marta Rodríguez-Sáiz, Marianna Lembo, Luca Bertetti, Roberto Muraca, Javier Velasco, Antonella Malcangi, Juan Luis De La Fuente, José Luis Barredo
R+D Biology, Antibióticos S.A., Avenida de Antibióticos 59-61, 24009 León, Spain.
An Acremonium chrysogenum strain improvement program based on the transformation with cephalosporin biosynthetic genes was carried out to enhance cephalosporin C production. Best results were obtained with cefEF and cefG genes, selecting transformants with increased cephalosporin C production and lower accumulation of biosynthetic intermediates. Phleomycin resistant transformants, designated B1 and C1, showed a single copy random integration event, higher levels of cefEF transcript and, according to immunoblotting analyses, higher amounts of deacetylcephalosporin C acetyltransferase (DAC-AT) protein than their parental strains. Moreover, DAC-AT activity was higher in the transformants. Plasmids carrying geneticin resistance markers based on the nptII gene from Tn5 and the aphI gene from Tn903 were constructed to transform again B1 and C1, showing that the cassette Pgdh-nptII-trpC was able to confer geneticin resistance to A. chrysogenum and demonstrating that geneticin is a helpful selection marker.
R&D Biology, Antibióticos S. A., Avenida de Antibióticos 59-61, E-24009 León, Spain.
Penicillin, discovered 75 years ago by Sir Alexander Fleming in Penicillium notatum, laid the foundations of modern antibiotic chemotherapy. Early work was carried out on the original Fleming strain, but it was later replaced by overproducing strains of Penicillium chrysogenum, which became the industrial penicillin producers. We show how a C(1357)-->T (A394V) change in the gene encoding PahA in P. chrysogenum may help to explain the drawback of P. notatum. PahA is a cytochrome P450 enzyme involved in the catabolism of phenylacetic acid (PA; a precursor of penicillin G). We expressed the pahA gene from P. notatum in P. chrysogenum obtaining transformants able to metabolize PA (P. chrysogenum does not), and observing penicillin production levels about fivefold lower than that of the parental strain. Our data thus show that a loss of function in P. chrysogenum PahA is directly related to penicillin overproduction, and support the historic choice of P. chrysogenum as the industrial producer of penicillin.
The clavulanic acid biosynthetic cluster of Streptomyces clavuligerus: genetic organization of the region upstream of the car gene.
Encarnación Mellado, Luis Miguel Lorenzana, Marta Rodríguez-Sáiz, Bruno Díez, Paloma Liras, José Luis Barredo
Area de Biotecnología, Antibióticos SA, Avenida de Antibióticos 59-61, 24009 León, Spain.
The genetic organization of the region upstream of the car gene of the clavulanic acid biosynthetic gene cluster of Streptomyces clavuligerus has been determined. Sequence analysis of a 12.1 kb region revealed the presence of 10 ORFs whose putative functions, according to database searches, are discussed. Three co-transcriptional units are proposed: ORF10-11, ORF12-13 and ORF15-16-17-18. Potential transcriptional terminators were identified downstream of ORF11 (fd) and ORF15. Targeted disruption of ORF10 (cyp) gave rise to transformants unable to produce clavulanic acid, but with a considerably higher production of cephamycin C. Transformants inactivated at ORF14 had a remarkably lower production of clavulanic acid and similar production of cephamycin C. Significant improvements of clavulanic acid production, associated with a drop in cephamycin C biosynthesis, were obtained with transformants of S. clavuligerus harbouring multiple copies of plasmids carrying different constructions from the ORF10-14 region. This information can be used to guide strain improvement programs, blending random mutagenesis and molecular cloning, to optimize the yield of clavulanic acid.
Methods Mol Biol. 2012 ;898 :133-51 22711122
Gadea Biopharma, Parque Tecnológico de León, León, Spain.
Mucor circinelloides is a β-carotene producing zygomycete amenable to metabolic engineering using molecular tools. The crtS gene of the heterobasidiomycetous yeast Xanthophyllomyces dendrorhous encodes the enzymatic activities β-carotene hydroxylase and ketolase, allowing this yeast to produce the xanthophyll called astaxanthin. Here we describe the fermentation of X. dendrorhous in astaxanthin producing conditions to purify mRNA for the cloning of the cDNA from the crtS gene by RT-PCR. Further construction of an expression plasmid and transformation of M. circinelloides protoplasts allow the heterologous expression of the crtS cDNA in M. circinelloides to obtain β-cryptoxanthin and zeaxanthin overproducing transformants. These two xanthophylls are hydroxylated compounds from β-carotene. These results show that the crtS gene is involved in the conversion of β-carotene into xanthophylls, being potentially useful to engineer carotenoid pathways.
Methods Mol Biol. 2012 ;892 :13-20 22623295
Department of Microbiology, Instituto Biomar, S.A. Parque Tecnológico de León, León, Spain, email@example.com.
Carotenoids are important pigments produced by plants and many microorganisms, including fungi, microalgae, cyanobacteria, and bacteria. Marine actinomycetes are a group of bacteria that produce a variety of metabolites with economic potential. Here, we describe a general method of selecting marine actinomycetes as carotenoids' producers. The screening is carried out at two levels: the first one involves a quick selection of strains by visual color inspection, and the second consists in the analysis of the extracts by HPLC. The taxonomic analysis of the producing strains gives us an overview of the groups of actinomycetes in which carotenoids can be found.
Mol Biotechnol. 2008 Nov 18;: 19016007
The NADP-dependent Glutamate Dehydrogenase Gene from the Astaxanthin Producer Xanthophyllomyces dendrorhous: Use of Its Promoter for Controlled Gene Expression.
R&D Biology, Antibióticos S.A, Avenida de Antibióticos 59-61, 24009, León, Spain.
The gdhA gene encoding the NADP-dependent glutamate dehydrogenase (GDH) activity from Xanthophyllomyces dendrorhous has been cloned and characterized, and its promoter used for controlled gene expression in this red-pigmented heterobasidiomycetous yeast. We determined the nucleotide sequence of a 4701 bp DNA genomic fragment, showing an open reading frame of 1871 bp interrupted by five introns with fungal consensus splice-site junctions. The predicted protein (455 amino acids; 49 kDa) revealed high identity to GDHs, especially to those from the fungi Cryptococcus neoformans (70%), Sclerotinia sclerotiorum (66%), and several species of Aspergillus (66-67%). Gene phylogenies support the grouping of X. dendrorhous GDH close to those from the majority of the filamentous fungi. The promoter region of the gdhA gene (PgdhA) contains a TATA-like box and two large pyrimidine stretches. The use of PgdhA for gene expression was validated by electrotransformation of X. dendrorhous using an in-frame fusion with the hygromycin resistance gene (hyg (R)) as a reporter. X. dendrorhous transformants were able to grow in YEME complex medium and in Czapek minimal medium supplemented with 50 mug/ml hygromycin, but gene expression in Czapek medium was repressed when using ammonium acetate as a nitrogen source. PgdhA is a valuable tool for controlled gene expression in Basidiomycetes.
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Acta Biochim Pol. 2012 ;59 (1):151-3 22428133
Section of Chemistry, Faculty of Chemical Engineering, Aristotle University of Thessaloniki, Greece.
The all-trans-β-carotene is a natural pigment used in various industrial fields (food, cosmetics, pharmaceuticals, etc) and possesses the higher provitamin A activity, in respect to other carotenoids. All-trans-β-carotene is produced industrially by chemical and biotechnological means. For β-carotene biotechnological production in industrial scale mated cultures of Blakeslea trispora, a heterothallic fungus, are mainly used. Despite the intense research for β-carotene production by B. trispora, natural substrate utilization has not been extensively studied. Solid agro-food wastes such as cabbage, watermelon husk and peach peels from northern Greece as main carbon source into submerged B. trispora cultures for carotenoids production, was examined. The media containing only the agro-food waste (2-4) gave a biomass accumulation 7.77 ± 0.4 g/L, while a reference medium 1 with glucose (10 g/L) gave 4.65 ± 0.21 g/L. In another experiments series agro-food wastes were used with corn steep liquor and thiamine (media 6-8), giving a biomass accumulation and total carotenoid volumetric production 10.2 ± 2.41 g/L and 230.49 ± 22.97 mg/L, respectively. These are the higher values reported for solid wastes so far in respect to those obtained from a synthetic medium, with higher glucose concentration of 50 g/L where the correspondent values were 9.41 ± 1.18 g/L and 45.63 mg/L respectively. The results support that B. trispora is able to utilize, almost equivalently, different origin agro-food wastes for carotenoids production. Furthermore, β-carotene percentage in all examined cases was over 76%, as it was estimated by HPLC analysis, suggesting that these agro food wastes may be used for high purity, large scale β carotene production.
Institute of Biological Engineering, Department of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, People's Republic of China.
Poly (β-L:-malic acid)(PMLA) is a water-soluble polyester with many attractive properties in chemical industry and medicine development. However, the low titer of PMLA in the available producer strains limits further industrialization efforts and restricts its many potential applications. In order to solve this problem, a new strain with the distinguished high productivity of PMLA was isolated from fresh plants samples. It was characterized as the candidate of Aureobasidium pullulans based on the morphology and phylogenetic analyses of the internal transcribed spacer sequences. After the optimization of culture conditions, the highest PMLA concentration (62.27 g l(-1)) could be achieved in the shake flask scale. In addition, the contribution of the carbon flux to exopolysaccharide (EPS) and PMLA could be regulated by the addition of CaCO₃ in the medium. This high-level fermentation process was further scaled up in the 10 l benchtop fermentor with a high PMLA concentration (57.2 g l(-1)) and productivity (0.35 g l(-1) h(-1)), which are the highest level in all the literature. Finally, the suitable acid hydrolysis conditions of PMLA were also investigated with regard to the production of L:-malic acid, and the kinetics of PMLA acid hydrolysis was modeled to simulate the whole degradation process. The present work paved the road to produce this multifunctional biomaterial (PMLA) at industrial scale and promised one alternative method to produce L:-malic acid in the future.
Biotechnol Adv. 2011 Apr 9;: 21497650
An economic assessment of astaxanthin production by large scale cultivation of Haematococcus pluvialis.
College of Biotechnology, Tianjin University of Science and Technology, Tianjin 300457, P.R. China.
Although natural sources have long been exploited for astaxanthin production, it is still uncertain if natural astaxanthin can be produced at lower cost than that of synthetic astaxanthin or not. In order to give a comprehensive cost analysis of astaxanthin production from Haematococcus, a pilot plant with two large scale outdoor photobioreactors and a raceway pond was established and operated for 2years to develop processes for astaxanthin production from Haematococcus. The developed processes were scaled up to a hypothetical plant with a production capacity about 900kg astaxanthin per year, and the process economics was preliminarily assessed. Based on the analysis, the production cost of astaxanthin and microalgae biomass can be as low as $718/kg and $18/kg respectively. The results are very encouraging because the estimated cost might be lower than that of chemically synthesized astaxanthin.
Julia Maria Naumann, Andy Zöllner, Călin-Aurel Drăgan, Josef Messinger, Joachim Adam, Matthias Bureik
PomBioTech GmbH, Campus Building A1-1, 66123, Saarbrücken, Germany.
The human sex hormone progesterone plays an essential and complex role in a number of physiological processes. Progesterone deficiency is associated with menstrual disorders and infertility as well as premature birth and abortion. For progesterone replacement therapy, the synthetic progestogen dydrogesterone is commonly used. In the body, this drug is metabolized to 20α-dihydrodydrogesterone (20α-DHD), which also shows extensive pharmacological effects and hence could act as a therapeutic agent itself. In this study, we describe an efficient biotechnological production procedure for 20α-DHD that employs the stereo- and regioselective reduction of dydrogesterone in a whole-cell biotransformation process based on recombinant fission yeast cells expressing the human enzyme AKR1C1 (20α-hydroxysteroid dehydrogenase, 20α-HSD). In a fed-batch fermentation at pilot scale (70 L) with a genetically improved production strain and under optimized reaction conditions, an average 20α-DHD production rate of 190 μM day(-1) was determined for a total biotransformation time of 136 h. Combined with an effective and reliable downstream processing, a continuous production rate of 12.3 ± 1.4 g 20α-DHD per week and fermenter was achieved. We thus established an AKR-dependent whole-cell biotransformation process that can also be used for the production of other AKR1C1 substrates (as exemplarily shown by the production of 20α-dihydroprogesterone in gram scale) and is in principle suited for the production of further human AKR metabolites at industrial scale.
Departamento de Biotecnología, Universidad Autónoma Metropolitana-Iztapalapa, Av. San Rafael Atlixco No. 186 Col. Vicentina, CP 09340, Distrito Federal, Mexico.
Owing to their health benefits, probiotics and prebiotics are nowadays widely used in yogurts and fermented milks, which are leader products of functional foods worldwide. The world market for functional foods has grown rapidly in the last three decades, with an estimated size in 2003 of ca US$ 33 billion, while the European market estimation exceeded US$ 2 billion in the same year. However, the production of probiotics and prebiotics at industrial scale faces several challenges, including the search for economical and abundant raw materials for prebiotic production, the low-cost production of probiotics and the improvement of probiotic viability after storage or during the manufacturing process of the functional food. In this review, functional foods based on probiotics and prebiotics are introduced as a key biotechnological field with tremendous potential for innovation. A concise state of the art addressing the fundamentals and challenges for the development of new probiotic- and prebiotic-based foods is presented, the niches for future research being clearly identified and discussed.
College of Chemical Engineering and Ecology, Guangxi University for Nationality, Nanning, 530007, China.
As a rare sugar alcohol, L-arabitol can be used in food and can prevent extra fat deposits in the intestinal tract. Commercially, L-arabitol is prepared from pure L-arabinose by hydrogenation, which needs a high temperature and high pressure, leading to a high production cost for Larabitol. Therefore, this study describes a novel L-arabitol production method based on biological purification from the xylitol mother liquor, a cheap and readily available raw material that contains a high concentration of Larabitol. First, a novel Bacillus megaterium strain was screened that can utilize xylitol, sorbitol, and mannitol, yet not L-arabitol. The isolated strain was inoculated into a medium containing the xylitol mother liquor under formulated culture conditions, where a high L-arabitol yield (95%) and high purity (80%) were obtained when the medium was supplemented with 50 g/l of xylitol mother liquor. Upon further purification of the fermentation broth by ion exchange and decolorization, L-arabitol was crystallized with a purity of 98.5%.
Metabolic engineering of Escherichia coli and Corynebacterium glutamicum for the production of L-threonine.
State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi 214122, China.
L-threonine is an essential amino acid for mammals and as such has a wide and expanding application in industry with a fast growing market demand. The major method of production of l-threonine is microbial fermentation. To optimize L-threonine production the fundamental solution is to develop robust microbial strains with high productivity and stability. Metabolic engineering provides an effective alternative to the random mutation for strain development. In this review, the updated information on genetics and molecular mechanisms for regulation of L-threonine pathways in Escherichia coli and Corynebacterium glutamicum are summarized, including L-threonine biosynthesis, intracellular consumption and trans-membrane export. Upon such knowledge, genetically defined L-threonine producing strains have been successfully constructed, some of which have already achieved the productivity of industrial producing strains. Furthermore, strategies for strain construction are proposed and potential problems are identified and discussed. Finally, the outlook for future strategies to construct industrially advantageous strains with respect to recent advances in biology has been considered.
Department of Plant and Environmental Sciences, The Institute of Life Sciences, Moshe Shilo Minerva Center for Marine Biogeochemistry, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel. firstname.lastname@example.org
In comparison with the thermophilic and the alkaliphilic extremophiles, halophilic microorganisms have as yet found relatively few biotechnological applications. Halophiles are involved in centuries-old processes such as the manufacturing of solar salt from seawater and the production of traditional fermented foods. Two biotechnological processes involving halophiles are highly successful: the production of beta-carotene by the green alga Dunaliella and the production of ectoine (1,4,5,6-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid), used as a stabilizer for enzymes and now also applied in cosmetic products, from moderately halophilic bacteria. The potential use of bacteriorhodopsin, the retinal protein proton pump of Halobacterium, in optoelectronic devices and photochemical processes is being explored, and may well lead to commercial applications in the near future. Demand for salt-tolerant enzymes in current manufacturing or related processes is limited. Other possible uses of halophilic microorganisms such as treatment of saline and hypersaline wastewaters, and the production of exopolysaccharides, poly-beta-hydroxyalkanoate bioplastics and biofuel are being investigated, but no large-scale applications have yet been reported.
Centre for Marine and Environmental Research, CIMA, Faculty of Sciences and Technology, Universidade do Algarve, Campus de Gambelas, 8005-139, Faro, Portugal.
Large-scale production has been the major obstacle to the success of many biopesticides. The spreading of microbial biocontrol agents against postharvest disease, as a safe and environmentally friendly alternative to synthetic fungicides, is quite dependent on their industrial mass production from low-cost raw materials. Considerable interest has been shown in using agricultural waste products and by-products from food industry as nitrogen and carbon sources. In this work, carob pulp aqueous extracts were used as carbon source in the production of the biocontrol agent Pantoea agglomerans PBC-1. Optimal sugar extraction was achieved at a solid/liquid ratio of 1:10 (w/v), at 25°C, for 1 h. Batch experiments were performed in shake flasks, at different concentrations and in stirred reactors at two initial inoculums concentrations, 10(6) and 10(7) cfu ml(-1). The initial sugar concentration of 5 g l(-1) allowed rapid growth (0.16 h(-1)) and high biomass productivity (0.28 g l(-1) h(-1)) and was chosen as the value for use in stirred reactor experiments. After 22 and 32 h of fermentation the viable population reached was 3.2 × 10(9) and 6.2 × 10(9) cfu ml(-1) in the fermenter inoculated at 10(6) cfu ml(-1) and 2.7 × 10(9) and 6.7 × 10(9) cfu ml(-1) in the bioreactor inoculated at 10(7) cfu ml(-1). A 78% reduction of the pathogen incidence was achieved with PBC-1 at 1 × 10(8) cfu ml(-1), grown in medium with carob extracts, on artificially wounded apples stored after 7 days at 25°C against P. expansum.
Generation of high rapamycin producing strain via rational metabolic pathway-based mutagenesis and further titer improvement with fed-batch bioprocess optimization.
Department of Chemical and Biological Engineering, Institute of Biological Engineering, Zhejiang University, Hangzhou 310027, Zhejiang, China.
Rapamycin is a triene macrolide antibiotic produced by Streptomyces hygroscopicus. Besides its wide application as an effective immunosuppressive agent, other important bioactivities have made rapamycin a potential drug lead for novel pharmaceutical development. However, the low titer of rapamycin in the original producer strain limits further industrialization efforts and restricts its use for other applications. Predicated on knowledge of the metabolic pathways related to rapamycin biosynthesis in S. hygroscopicus, we have rationally designed approaches to generate a rapamycin high producer strain of S. hygroscopicus HD-04-S. These have included alleviation of glucose repression, improved tolerance towards lysine and shikimic acid, and auxotrophy of tryptophan and phenylalanine through the application of stepwise UV mutagenesis. The resultant strain produced rapamycin at 450 mg/L in the shake flask scale. These fermentations were further scaled up in 120 and 20,000 L fermentors, respectively, at the pilot plant. Selected fermentation factors including agitation speed, pH, and on-line supplementation were systematically evaluated. A fed-batch strategy was established to maximize rapamycin production. With these efforts, an optimized fermentation process in the larger scale fermentor was developed. The final titer of rapamycin was 812 mg/L in the 120 L fermentor and 783 mg/L in the 20,000 L fermentor. This work highlights a high rapamycin producing strain derived by mutagenesis and subsequent screening, fermentation optimization of which has now made it feasible to produce rapamycin on an industrial scale by fermentation. The strategies developed here should also be applicable to titer improvement of other important microbial natural products on an industrial scale.