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.

The present invention relates to a tumor-targeting Salmonella gallinarum strain and the use thereof. The tumor-targeting Salmonella gallinarum strain has excellent tumor proliferation inhibitory activity and enables tumor-specific targeting, and thus can be utilized for treatment and imaging of tumors without any side effects.

The present invention relates to recombinant Escherichia coli (E. coli) host cells comprising, in relation to wild-type cells, at least one mutation selected from the group consisting of deletion of the gene relA (relA); amino acid substitutions R290E and K292D in the protein guanosine-3,5-bis pyrophosphate 3-pyrophosphohydrolase (bifunctional (p)ppGpp synthetase II; SpoT) (spo T[R290E;K292D]); and amino acid substitution G267C in the protein pyruvate dehydrogenase subunit E1 (AceE) (aceE[G267C]). Said recombinant host cells are characterized by increased sugar uptake rates that lead to increased productivity when using said cells for the production of biosynthetic products. The present invention further relates to respective methods for the biosynthetic production of a product of interest using said host cells.

The present invention relates to a cell which is genetically modified over its wild type in such a way that it has a reduced ppGppase activity relative to its wild type, and preferably an essential amino acid, even more preferably an essential amino acid derived from serine, most preferably methionine or tryptophan, to a feed additive comprising such a cell, to a method of preparing a cell overproducing essential amino acid, more preferably an essential amino acid derived from serine, most preferably methionine or tryptophan, comprising preparing a cell having a knocked-out gene coding for a ppGppase, and to a method of preparing an essential amino acid, more preferably an essential amino acid derived from serine, most preferably methionine or tryptophan, comprising the steps of a) culturing the cell according to the first aspect of the present invention or to any of its embodiments, and b) optionally: purifying the amino acid.