The invention discloses a genetically engineered bacterium in which the gene encoding adenine deaminase on the genome of the bacterium is knocked out or/and the gene encoding the enzyme in the NAD.sup.+ anabolic pathway is integrated on the genome of the bacterium. The invention also discloses a construction method of the above-mentioned genetically engineered bacteria. The gene encoding adenine deaminase on the genome of the host strain is knocked out to obtain a strain with high NAD.sup.+ yield. Or the expression cassettes of the gene encoding the enzyme in the NAD.sup.+ synthesis pathway are constructed separately, and then the enzyme encoding The gene expression cassette is integrated into the genome of the host strain whose gene encoding adenine deaminase is knocked out to construct a strain with high NAD.sup.+ production. The application of the above genetically engineered bacteria is disclosed. A method of producing NAD.sup.+ is disclosed.

The present invention relates to microbial production of nicotinamide mononucleotide (NMN), nicotinamide riboside (NR), and nicotinamide adenine dinucleotide (NAD) using a genetically modified bacterium.

The present invention relates to a method of detecting the presence of a bacterial and/or fungal cell in a sample through detecting the presence of nicotinamidase activity or nicotinamidase, wherein the presence of nicotinamidase activity or nicotinamidase indicates the presence of a bacterial and/or fungal cell in the sample. The invention also relates to a method for monitoring bacterial and/or fungal cell contamination in a cell of tissue culture comprising detecting the presence of nicotinamidase activity or nicotinamidase in the cell or tissue culture.

The invention discloses a genetically engineered bacterium in which the gene encoding adenine deaminase on the genome of the bacterium is knocked out or/and the gene encoding the enzyme in the NAD.sup.+ anabolic pathway is integrated on the genome of the bacterium. The invention also discloses a construction method of the above-mentioned genetically engineered bacteria. The gene encoding adenine deaminase on the genome of the host strain is knocked out to obtain a strain with high NAD.sup.+ yield. Or the expression cassettes of the gene encoding the enzyme in the NAD.sup.+ synthesis pathway are constructed separately, and then the enzyme encoding The gene expression cassette is integrated into the genome of the host strain whose gene encoding adenine deaminase is knocked out to construct a strain with high NAD.sup.+ production. The application of the above genetically engineered bacteria is disclosed. A method of producing NAD.sup.+ is disclosed.

There is described herein a plant cell having modulated expression or activity of a nicotinamidase enzyme, said plant cell comprising: (a) a polynucleotide sequence comprising, consisting or consisting essentially of a sequence encoding the nicotinamidase enzyme; or (b) a polypeptide encoded by the polynucleotide set forth in (a); wherein said plant cell comprises at least one modification which modulates the expression or activity of the polynucleotide or the polypeptide as compared to a control plant cell in which the expression or activity of the polynucleotide or polypeptide has not been modified. Furthermore, said poly nucleotide (a) of said plant cell comprises: (i) a polynucleotide comprising, consisting or consisting essentially of a sequence having at least 70% sequence identity to SEQ ID NO:1, SEQ ID NO:3, SEQ ID NO:5, SEQ ID NO:7, SEQ ID NO:9, SEQ ID NO:11, SEQ ID NO:13, SEQ ID NO:15, SEQ ID NO:17, SEQ ID NO:19 SEQ ID NO:24 or SEQ ID NO:26; and/or (ii) a construct, vector or expression vector comprising the isolated polynucleotide set forth in (i) or set forth in SEQ ID NO:21. Furthermore, wherein said polypeptide (b) of said plant cell comprises: a polypeptide encoded by the polynucleotide set forth above; and/or a polypeptide comprising, consisting or consisting essentially of a sequence having at least 90% sequence identity to SEQ ID NO:2, SEQ ID NO:4, SEQ ID NO:6, SEQ ID NO:8, SEQ ID NO:10, SEQ ID NO:12, SEQ ID NO:14, SEQ ID NO:16, SEQ ID NO:18, SEQ ID NO:20, SEQ ID NO:25 or SEQ ID NO:27.

Stress tolerance in plants and plant cells is achieved by using nucleotide sequences encoding enzymes involved in the NAD salvage synthesis pathway and/or the NAD de novo synthesis pathway e.g. for overexpression in plants.