Deletion of one of two Escherichia coli genes encoding putative Na+/H+ exchangers (ycgO) perturbs cytoplasmic alkali cation balance at low osmolarity.
Two genes in the Escherichia coli genome, b4065 (yjcE) and b1191 (ycgO), are similar to genes encoding eukaryotic Na+/H+ exchangers. Mutants were constructed in which yjcE (GRN11), ycgO (GRF55) or both (GRD22) were inactivated. There was no change in respiration-driven Na+ efflux in any of the mutants when grown in media containing 50-500 mM Na+. The only striking finding was that growth of GRF55 was impaired at low osmolarity. In complex low-salt medium, GRF55 grew at a wild-type rate for three to four generations but then stopped; the growth was partially recovered after a pause, the length of which was dependent on salt concentration. Measurement of cytoplasmic alkali cations showed that an abrupt loss of about one-half of the intracellular K+ preceded the pause. When grown in low-salt medium with only 20 mM added Na+, GRF55 also lost the ability to maintain a sodium concentration gradient. However, this phenomenon appears to be a secondary effect of the ycgO deletion. The double mutant GRD22 has the same properties as GRF55; no additional effect was found. The data indicate that neither ycgO nor yjeE participates in respiration-driven Na+ extrusion. Instead, ycgO is required for growth at low osmolarity. Hence it is concluded that ycgO participates in cell volume regulation, and accordingly it is suggested that ycgO be renamed cvrA.
Verkhovskaya
M L
ML
Helsinki Bioenergetics Group, Institute of Biotechnology, PO Box 56 (Viikinkaari 5), FIN-00014 University of Helsinki, Finland. Marina.Verkhovskaya@Helsinki.Fi
Barquera
B
B
Wikström
M
M
D000595:Amino Acid Sequence; D001692:Biological Transport; D027682:Cation Transport Proteins; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000502:physiology*; D005798:Genes, Bacterial; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials; D008969:Molecular Sequence Data; D009154:Mutation; D009994:Osmolar Concentration; D010100:Oxygen / Q000378:metabolism; D010641:Phenotype; D010957:Plasmids / Q000235:genetics; D011188:Potassium / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000502:physiology*
D027682:Cation Transport Proteins; D029968:Escherichia coli Proteins; D017923:Sodium-Hydrogen Exchangers; D012964:Sodium; D011188:Potassium; D010100:Oxygen