Genome rearrangements in Bradyrhizobium japonicum field isolates.

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Among Bradyrhizobium japonicum field isolates, I found abnormal isolates (HRS isolates) which possesses many copies of prokaryotic insertion sequences (IS), RS-alpha, RS-beta and others. We obtained physical evidence for genome rearrangements in B.japonicum HRS isolates. The symbiotic regions (nif, nod and hup) in a HRS genome were heavily subjected to insertion, deletion and other types of genome rearrangements. HRS isolates had a tandem repeat RS-alpha dimer, which may give rise to a burst of transpositional rearrangements.Because snapback analysis showed the presence of the pairs of ISs in an opposite direction, these structures correspond to type II transposon, a compound transposon. In order to examine whether the potential compound transposon may contribute to horizontal transfer of symbiotic genes, I developed to detect nod gene transfer on agar media from B.japonicum HRS isolates to B.elkanii USDA94deltaNOD,a mutant defective in nod genes. As a result, we could obtained B.elkanii cells which acquired the nod region of the HRS isolate and IS element, FK1. The B.elkanii cells restored nodulation phenotype to siratro and production of lipo-chitin nodulation signals.