1-AMINOCYCLOPROPANE-1-CARBOXYLATE (ACC) DEAMINASE GENES IN RHIZOBIA: ISOLATION AND CHARACTERIZATION
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A collection of 233 putative Rhizobia strains from 30 different sites across Saskatchewan, Canada was assayed for ACC deaminase activity, with 27 of the strains displaying activity. When all 27 strains were characterized based on 16S rRNA gene sequences, it was noted that 26 strains are Rhizobium leguminosarum and one strain is Rhizobium gallicum. PCR was used to rapidly isolate ACC deaminase structural genes from the above mentioned 27 strains; 17 of them have 99% identities when compared with the previously characterized ACC deaminase structural gene (acdS) from Rhizobium leguminosarum bv. viciae 128C53K, whereas the other 10 strains are 83% identical compared to the acdS of R. leguminosarum bv. viciae 128C53K. Southern hybridization showed that each strain has only one ACC deaminase gene. Using inverse PCR, the region upstream of the ACC deaminase structural genes was characterized for all 17 strains and shown to encode a leucine responsive regulatory protein. The results are discussed in the context of a previously proposed model for the regulation of bacterial ACC deaminase and facilitates an elaboration of the role of ACC deaminase in nodulation and nitrogen fixation.