REGULATION OF THE ESCHERICHIA-COLI WATER CHANNEL GENE AQPZ

Osmotic movement of water across bacterial cell membranes is postulate d to be a homeostatic mechanism for maintaining cell turgor, The molec ular water transporter remained elusive until discovery of the Escheri chia coli water channel, AqpZ, however the regulation of the aqpZ gene expression and physiological function of the AqpZ protein are unknown . Northern analysis revealed a transcript of 0.7 kb, confirming the mo nocistronic nature of aqpZ Regulatory studies performed with an aqpZ:: lacZ low copy plasmid demonstrate enhanced expression during mid-logar ithmic growth, and expression of the gene is dependent upon the extrac ellular osmolality, which increased in hypoosmotic environments but st rongly reduced in hyperosmolar NaCl or KCI, While disruption of the ch romosomal aqpZ is not lethal for E, coli, the colonies of the aqpZ kno ckout mutant are smaller than those of the parental wild-type strain, When cocultured with parental wild-type E, coli, the aqpZ knockout mut ant exhibits markedly reduced colony formation when grown at 39 degree s C, Similarly, the aqpZ knockout mutant also exhibits greatly reduced colony formation when grown at low osmolality, but this phenotype is reversed by overexpression of AqpZ protein, These results implicate Aq pZ as a participant in the adaptive response of E, coli to hypoosmotic environments and indicate a requirement for AqpZ by rapidly growing c ells.