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Query: UMLS:C1832526 (PCC)
 5,967 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

D-Mannitol (hereafter denoted mannitol) is used in the medical and food industry and is currently produced commercially by chemical hydrogenation of fructose or by extraction from seaweed. Here, the marine cyanobacterium Synechococcus sp. PCC 7002 was genetically modified to photosynthetically produce mannitol from CO2 as the sole carbon source. Two codon-optimized genes, mannitol-1-phosphate dehydrogenase (mtlD) from Escherichia coli and mannitol-1-phosphatase (mlp) from the protozoan chicken parasite Eimeria tenella, in combination encoding a biosynthetic pathway from fructose-6-phosphate to mannitol, were expressed in the cyanobacterium resulting in accumulation of mannitol in the cells and in the culture medium. The mannitol biosynthetic genes were expressed from a single synthetic operon inserted into the cyanobacterial chromosome by homologous recombination. The mannitol biosynthesis operon was constructed using a novel uracil-specific excision reagent (USER)-based polycistronic expression system characterized by ligase-independent, directional cloning of the protein-encoding genes such that the insertion site was regenerated after each cloning step. Genetic inactivation of glycogen biosynthesis increased the yield of mannitol presumably by redirecting the metabolic flux to mannitol under conditions where glycogen normally accumulates. A total mannitol yield equivalent to 10% of cell dry weight was obtained in cell cultures synthesizing glycogen while the yield increased to 32% of cell dry weight in cell cultures deficient in glycogen synthesis; in both cases about 75% of the mannitol was released from the cells into the culture medium by an unknown mechanism. The highest productivity was obtained in a glycogen synthase deficient culture that after 12 days showed a mannitol concentration of 1.1 g mannitol L(-1) and a production rate of 0.15 g mannitol L(-1) day(-1). This system may be useful for biosynthesis of valuable sugars and sugar derivatives from CO2 in cyanobacteria.
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PMID:Engineering of photosynthetic mannitol biosynthesis from CO2 in a cyanobacterium. 2426 97

The genetic engineering of microbial cell factories is a sustainable alternative to the chemical synthesis of organic compounds. Successful metabolic engineering often depends on manipulating several enzymes, requiring multiple transformation steps and selection markers, as well as protein assembly and efficient substrate channeling. Naturally occurring fusion genes encoding two or more enzymatic functions may offer an opportunity to simplify the engineering process and to generate ready-made protein modules, but their functionality in heterologous systems remains to be tested. Here we show that heterologous expression of a fusion enzyme from the marine alga Micromonas pusilla, comprising a mannitol-1-phosphate dehydrogenase and a mannitol-1-phosphatase, leads to synthesis of mannitol by Escherichia coli and by the cyanobacterium Synechococcus sp. PCC 7002. Neither of the heterologous systems naturally produce this sugar alcohol, which is widely used in food, pharmaceutical, medical, and chemical industries. While the mannitol production rates obtained by single-gene manipulation were lower than those previously achieved after pathway optimization with multiple genes, our findings show that naturally occurring fusion proteins can offer simple building blocks for the assembly and optimization of recombinant metabolic pathways.
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PMID:Engineering Mannitol Biosynthesis in Escherichia coli and Synechococcus sp. PCC 7002 Using a Green Algal Fusion Protein. 3040 53