Abstract: A bacterium for producing L-amino acid has improved expression of a polynucleotide encoding a protein represented by SEQ ID NO:3 and improved expression of a polynucleotide encoding a protein represented by SEQ ID NO:31, and/or has mutations in bases at positions ?45 bp and ?47 bp of a promotor region represented by SEQ ID NO:57. A polynucleotide, encodes proteins and can be included in a recombinant vector, which can be included in a recombinant strain. These are useful in a method for producing L-amino acid. The polynucleotide encodes a protein which is represented by SEQ ID NO:3 and has arginine at position 334 substituted by a terminator or encodes a protein which is represented by SEQ ID NO:31 and has tyrosine at position 592 substituted by phenylalanine, or is formed by mutations in bases at positions ?45 bp and ?47 bp of a promotor region represented by SEQ ID NO:57.

Abstract: Provided are a method for introducing point mutations to the coding sequence of NCg12176 gene or improving the expression thereof in Corynebacterium glutamicum, and a method for performing point mutations on the promoter region sequence of dapB gene in Corynebacterium glutamicum. The fermentation yield of L-lysine produced by a strain with the mutations can be increased by means of the methods.

Abstract: A method for screening for target cells, a corresponding test kit and a use thereof, a method for screening cells, and a biological culture chip and a preparation method therefor and a use thereof. The method for screening target cells comprises: culturing said candidate single cells within a culture chamber provided with a signal screening layer, the signal screening layer comprising signal molecules for specific recognition of target molecules; on the basis of signals of the signal molecules, selecting target cells suitable for secreting the target molecules. The method for screening cells comprises: arranging candidate cells in a culture chamber to form target antibody-antigen-signal antibody complexes; on the basis of signals of signal molecules connected to the signal antibodies, determining whether the candidate cells are target cells. The biological culture chip comprises a matrix (100), and a biological culture space arranged on the surface of the matrix (100) and used for culturing biological cells.

Abstract: An Escherichia coli-based kdtA-gene-modified recombinant strain, a construction method therefor and use thereof are provided. A mutant gene obtained by subjecting a wild-type kdtA gene (ORF sequence is shown in a sequence 73556-74833 in GenBank accession No. CP032667.1), a wild-type spoT gene (ORF sequence is shown in a sequence 3815907-3818015 in GenBank accession No. AP009048.1) and a wild-type yebN gene (ORF sequence is shown in a sequence 1907402-1907968 in GenBank accession No. AP009048.1) of an E. coli K12 strain and a derivative strain thereof (such as MG1655 and W3110) to site-directed mutagenesis, and a recombinant strain obtained therefrom can be used for the production of L-threonine. Compared with an unmutated wild-type strain, the obtained strain can produce L-threonine with a higher concentration and has good strain stability, and also has lower production cost as an L-threonine production strain.