NH 4 + transport system of a psychrophilic marine bacterium, Vibrio sp. strain ABE-1

NH 4 + transport system of a psychrophilic marine bacterium Vibrio sp. strain ABE-1 ( Vibrio ABE-1) was examined by measuring the uptake of [ 14 C]methylammonium ion ( 14 CH 3 NH 3 + ) into the intact cells. 14 CH 3 NH 3 + uptake was detected in cells grown in medium containing glutamate as the sole nitrogen source, but not in those grown in medium containing NH 4 Cl instead of glutamate. Vibrio ABE-1 did not utilize CH 3 NH 3 + as a carbon or nitrogen source. NH 4 Cl and nonradiolabeled CH 3 NH 3 + completely inhibited 14 CH 3 NH 3 + uptake. These results indicate that 14 CH 3 NH 3 + uptake in this bacterium is mediated via an NH 4 + transport system and not by a specific carrier for CH 3 NH 3 + . The respiratory substrate succinate was required to drive 14 CH 3 NH 3 + uptake and the uptake was completely inhibited by KCN, indicating that the uptake was energy dependent. The electrochemical potentials of H + and/or Na + across membranes were suggested to be the driving forces for the transport system because the ionophores carbonylcyanide m -chlorophenylhydrazone and monensin strongly inhibited uptake activities at pH 6.5 and 8.5, respectively. Furthermore, KCl activated 14 CH 3 NH 3 + uptake. The 14 CH 3 NH 3 + uptake activity of Vibrio ABE-1 was markedly high at temperatures between 0° and 15°C, and the apparent K m value for CH 3 NH 3 + of the uptake did not change significantly over the temperature range from 0° to 25°C. Thus, the NH 4 + transport system of this bacterium was highly active at low temperatures.