The present invention relates to glucoamylase variants having improved thermostability. The present invention also relates to polynucleotides encoding the variants; nucleic acid constructs, vectors, and host cells comprising the polynucleotides; and methods of using the variants.

The present disclosure discloses a thermophilic L-asparaginase mutant and screening and fermentation methods thereof, and belongs to the field of gene engineering, enzyme engineering and fermentation engineering. In Bacillus subtilis 168, a Pyrococcus yayanosii CH1-derived L-asparaginase encoding gene is used as a template, and a mutation library is constructed by an error-prone PCR (epPCR) technology. A mutant strain with improved specific enzyme activity is screened through a high-flux screening method of synchronous cell disruption and enzyme activity measurement. Mutated residues included in a positive mutant are analyzed to construct a composite mutant strain S17G/A90S/R156S/K272A with improved specific enzyme activity and specific enzyme activity of 3108 U/mg. An expression quantity of the composite mutant strain in the Bacillus subtilis 168 is increased through measures of a strong promoter P.sub.43 and RBS optimization. Finally, the Bacillus subtilis 168 with a gene of the L-asparaginase composite mutant strain is subjected to enzyme production fermentation in a 5 L fermentation tank through culture medium optimization and pH and feeding coupling strategies. The enzyme activity yield of the L-asparaginase is up to 6453+/−127 U/mL.

The present disclosure discloses a thermophilic L-asparaginase mutant and screening and fermentation methods thereof, and belongs to the field of gene engineering, enzyme engineering and fermentation engineering. In Bacillus subtilis 168, a Pyrococcus yayanosii CH1-derived L-asparaginase encoding gene is used as a template, and a mutation library is constructed by an error-prone PCR (epPCR) technology. A mutant strain with improved specific enzyme activity is screened through a high-flux screening method of synchronous cell disruption and enzyme activity measurement. Mutated residues included in a positive mutant are analyzed to construct a composite mutant strain S17G/A90S/R156S/K272A with improved specific enzyme activity and specific enzyme activity of 3108 U/mg. An expression quantity of the composite mutant strain in the Bacillus subtilis 168 is increased through measures of a strong promoter P.sub.43 and RBS optimization. Finally, the Bacillus subtilis 168 with a gene of the L-asparaginase composite mutant strain is subjected to enzyme production fermentation in a 5 L fermentation tank through culture medium optimization and pH and feeding coupling strategies. The enzyme activity yield of the L-asparaginase is up to 6453+/−127 U/mL.

The present invention relates to glucoamylase variants having improved thermostability. The present invention also relates to polynucleotides encoding the variants; nucleic acid constructs, vectors, and host cells comprising the polynucleotides; and methods of using the variants.

The present invention relates to glucoamylase variants having improved thermostability. The present invention also relates to polynucleotides encoding the variants; nucleic acid constructs, vectors, and host cells comprising the polynucleotides; and methods of using the variants.

The invention relates to the technical field of bioengineering, and discloses a method for synthesizing L-aspartic acid with maleic acid by whole-cell biocatalysis. In the invention, a recombinant strain co-expressing maleate cis-trans isomerase and L-aspartate lyase is constructed, and engineered and optimized to produce L-aspartic acid from maleic acid with a high conversion rate by whole-cell catalyzing. Relatively inexpensive maleic acid is utilized by the recombinant strain to produce L-aspartic acid, where maleic acid is reacted completely in 40-120 min, there is almost no buildup of the intermediate fumaric acid, and the conversion rate is up to 98% or more.

The invention relates to the technical field of bioengineering, and discloses a method for synthesizing L-aspartic acid with maleic acid by whole-cell biocatalysis. In the invention, a recombinant strain co-expressing maleate cis-trans isomerase and L-aspartate lyase is constructed, and engineered and optimized to produce L-aspartic acid from maleic acid with a high conversion rate by whole-cell catalyzing. Relatively inexpensive maleic acid is utilized by the recombinant strain to produce L-aspartic acid, where maleic acid is reacted completely in 40-120 min, there is almost no buildup of the intermediate fumaric acid, and the conversion rate is up to 98% or more.

It is an object of the present invention to provide a bacterial strain that can decrease the amount of an intermediate Compound P converted into Metabolite M and efficiently accumulate Compound P in a medium that is not supplemented with Metabolite M or the final product generated from Metabolite M. The present invention provides a prokaryotic organism having all features (a) to (d) as defined in the specification so as to accumulate Compound P by regulating expression level of Enzyme X that converts Compound P as an intermediate metabolite into Metabolite M in a biosynthetic pathway in which Metabolite M indispensable for the growth is produced from a carbon source.

It is an object of the present invention to provide a bacterial strain that can decrease the amount of an intermediate Compound P converted into Metabolite M and efficiently accumulate Compound P in a medium that is not supplemented with Metabolite M or the final product generated from Metabolite M. The present invention provides a prokaryotic organism having all features (a) to (d) as defined in the specification so as to accumulate Compound P by regulating expression level of Enzyme X that converts Compound P as an intermediate metabolite into Metabolite M in a biosynthetic pathway in which Metabolite M indispensable for the growth is produced from a carbon source.

The invention relates to the technical field of bioengineering, and discloses a method for synthesizing L-aspartic acid with maleic acid by whole-cell biocatalysis. In the invention, a recombinant strain co-expressing maleate cis-trans isomerase and L-aspartate lyase is constructed, and engineered and optimized to produce L-aspartic acid from maleic acid with a high conversion rate by whole-cell catalyzing. Relatively inexpensive maleic acid is utilized by the recombinant strain to produce L-aspartic acid, where maleic acid is reacted completely in 40-120 min, there is almost no buildup of the intermediate fumaric acid, and the conversion rate is up to 98% or more.