A methylamine-resistant mutant strain (4m3) of ATCC 29413 was capable of growth at pH 7·0, but not at pH 9·0, in the presence of concentrations of methylamine that totally inhibited growth of the parent strain. Strain 4m3 showed a marked reduction, at pH 7·0 but not at pH 9·0, in the initial rapid and slower second phases of uptake of [C]methylamine and ammonia, when compared with the parent strain, The rate of inhibition of nitrogenase activity, on adding ammonia at pH 7·0, was lower in strain 4m3 than in the parent strain and was attributable to a defect in the CHNH /NH transport system. Evidence that the second slower phase of [C]methylamine uptake is associated with metabolism via glutamine synthetase (GS) was obtained using mutant strains partially deficient in GS. Unlike these GS-deficient strains, strain 4m3 did not liberate ammonia extracellularly unless treated with L-methionine-DL-sulphoximine. Growth of strain 4m3 in medium containing 3 mM-methylamine resulted in a restoration of the first phase of [C]methylamine uptake, at pH 7·0, but not of ammonia uptake. However, growth in the presence of 3 mM-ammonia did not enhance the uptake of either methylamine or ammonia. Strain 4m3 is apparently deficient in the active CHNH /NH transport system, but has a CHNH transport system which can be induced by growth in the presence of methylamine.


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