Method for producing spermidine by using cheap substrates and engineering bacterium
A spermidine and spermidine decarboxylase technology, applied in the field of bioengineering, can solve the problems of undiscovered microorganisms, low spermidine content and the like
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Embodiment 1
[0073] Embodiment 1: Mutation and screening of carboxyspermidine dehydrogenase
[0074] Carboxyspermidine dehydrogenase gene rscsdh was cloned from Rhodobacter sphaeroides ATCC BAA-808. The accession NO of the amino acid sequence on NCBI is YP_351518.1. The expressed product is used to synthesize carboxyspermidine. The cloned genes were respectively connected to the pETDuet-1 vector, transformed into Escherichia coli BL21(DE), and expressed and purified. Induced expression purification method: the recombinant Escherichia coli is transferred to LB fermentation medium (peptone 10g / L, yeast powder 5g / L, NaCl 10g / L) in the amount of 2% by volume ratio, when the cell OD 600 After reaching 0.6-0.8, add IPTG with a final concentration of 0.4mM, induce expression and culture at 20°C for 8h. After induction of expression, the cells were collected by centrifugation at 4°C, 8000 rpm, and 20 minutes. After cell destruction, the enzyme was purified by the histag tag method, and the act...
Embodiment 2
[0076] Example 2: Mutation and screening expression of carboxyspermidine decarboxylase
[0077]The carboxyspermidine decarboxylase gene bccsdc (amino acid sequence is EEF87925.1) was obtained from Bacteroides cellulosilyticus DSM 14838. Induced expression and purification were performed in the same manner as in Example 1. Using isocarboxyspermidine as a substrate, the specific activity of the enzyme expressed by carboxyspermidine decarboxylase gene bccsdc is measured as 0 U / mg. Referring to the aforementioned "5. High-throughput screening of random mutations of enzymes", the genes bccsdc1 and bccsdc2 with the highest enzyme activity were obtained by random mutation screening, and their nucleic acid sequences are shown in SEQ ID NO:3 and SEQ ID NO:4. The specific activities of the expressed enzymes were: 32.1, 56.6U / mg.
Embodiment 3
[0078] Embodiment 3: the construction of the recombinant Escherichia coli expressing 6 kinds of enzymes simultaneously
[0079] Construction of recombinant Escherichia coli: six genes (γ-glutamate kinase ecggk, glutamate-5-semialdehyde dehydrogenase ecgsd, carboxyspermidine dehydrogenase rscsdh, carboxyspermidine decarboxylase bccsdc, glucose dehydrogenase Hydrogenase bsgdh, polyphosphate kinase 2-I smpkk) were connected to pETDuet-1, pACYCDuet-1, pRSFDuet-1 or pCDFduet-1 plasmids respectively, each plasmid expressed 2 kinds of genes, and each gene contained T7 promoter and RBS junction, with T7 terminator behind the gene. The 3 recombinant plasmids were transformed into E. coli Escherichia coli BL21, and the positive transformants were obtained by screening with a mixed antibiotic plate, that is, 6 recombinant E. coli that could enhance the expression of 6 genes as shown in Table 1 were obtained.
[0080] Construct the whole cell transformation production system, the whole c...
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