Ammonium (methylammonium) transport by Azospirillum spp

In recent years soil bacteria of the genus Azospirillum found increasing biological and ecological interest because of their ability to microaerobically fix N 2 and to live in close association with plant roots, stimulating growth of nitrogenlimited plants [1-5]. The physiology of N 2 fixation, especially its repression by N H + , has been studied extensively [6-9]. The question, however, how NH~traverses the membrane of these organisms has not yet been studied. In a number of soil bacteria, N H + uptake is mediated by specific carriers [10]. The results presented here also indicate the existence of a specific NH~carrier in Azospirillum.