Phosphate sensing microbial gene switch

A genetically engineered bacterium comprising:

• (i) a first gene expression cassette comprising a recombinant DNA molecule comprising a phosphate-sensitive promoter of a bacterial pstS phosphate ABC transporter gene operably linked to DNA encoding a transcript comprising a ribosome binding site (RBS) operably linked to a transcriptional repressor protein coding region,
• wherein the phosphate-sensitive promoter comprises a sequence having at least 95% sequence identity to SEQ ID NO:
• 515 and comprising the sequences of SEQ ID NO:
• 525, 526, 527, 528, and 529, wherein the RBS comprises SEQ ID NO:
• 449, and wherein the transcriptional repressor protein coding region encodes a bacterial TetR repressor protein;
• and
• (ii) a second gene expression cassette comprising a recombinant DNA molecule comprising a promoter which is repressed by the transcriptional repressor protein and which is operably linked to a DNA sequence encoding a bacterial glutamine synthetase
• wherein the promoter in the second gene expression cassette comprises a Ptet promoter;
• wherein the genetically engineered bacterium is of the genus Kosakonia and releases a greater amount of ammonia when grown in liquid culture under microaerobic conditions when inoculated in the presence of 0 mM inorganic phosphate than when grown in liquid culture under microaerobic conditions when inoculated in the presence of 20 mM inorganic phosphate.