NH4+ transport system of a psychrophilic marine bacterium, Vibrio sp strain ABE-1

NH4+ transport system of a psychrophilic marine bacterium Vibrio sp. strain ABE-1 (Vibrio ABE-1) was examined by measuring the uptake of [C-14]methyla mmonium ion ((CH3NH3+)-C-14) into the intact cells. (CH3NH3+)-C-14 uptake w as detected in cells grown in medium containing glutamate as the sole nitro gen source, but not in those grown in medium containing NH4Cl instead of gl utamate. Vibrio ABE-1 did not utilize CH3NH3+ as a carbon or nitrogen sourc e. NH4Cl and nonradiolabeled CH3NH3+ completely inhibited (CH3NH3+)-C-14 up take. These results indicate that (CH3NH3+)-C-14 uptake in this bacterium i s mediated via an NH4+ transport system and not by a specific carrier for C H3NH3+. The respiratory substrate succinate was required to drive (CH3NH3+) -C-14 uptake and the uptake was completely inhibited by KCN, indicating tha t the uptake was energy dependent. The electrochemical potentials of H+ and /or Na+ across membranes were suggested to be the driving forces for the tr ansport system because the ionophores carbonylcyanide m-chlorophenylhydrazo ne and monensin strongly inhibited uptake activities at pH 6.5 and 8.5, res pectively. Furthermore, KCl activated (CH3NH3+)-C-14 uptake. The (CH3NH3+)- C-14 uptake activity of Vibrio ABE-1 was markedly high at temperatures betw een 0 degrees and 15 degrees C, and the apparent K-m value for CH3NH3+ of t he uptake did not change significantly over the temperature range from 0 de grees to 25 degrees C. Thus, the NH4+ transport system of this bacterium wa s highly active at low temperatures.