Characterization of fast-growing Rhizobium japonicum isolated from korea

Abstract

$\underline{Rhizobium} \underline{japonicum}$ strains have been isolated from soybean root nodules collected throughout the country to study their several characteristics. The isolates were divided into two groups according to their growth rates. Fast growing isolates produced acid on yeast extract mannitol medium, while slow growing isolates not. Sucrose was utilized by the strains of fast growing isolates and slow growing isolates did not grow on sucrose as the sole carbon source. A modified gel electrophoresis technique provided a reproducible way of dectecting plasmids with molecular weight ranging from 50 to 600 kb harboured in fast growing isolates. One isolate, $\underline{R}$. $\underline{japonicum}$ R-41, contained only one ccc-DNA and four strains showed more than one plasmid band. Selected strain, $\underline{R}$. $\underline{japonicum}$ R-271, has three plasmids. The smallest plasmid, pRja271a, was eliminated by incubation at high temperature. This cured strain did not lose nodulation ability suggesting that pRja271a is not related to symbiosis. Large plasmids from fast-growers did not have any DNA homology with $\underline{nif}$ structural gene of $\underline{Klebsiella} \underline{pneumoniae}$. Homology bands were detected from the total DNA of $\underline{R}$. $\underline{japonicum}$ R-271 digested with various restriction enzyme, single band in HindIII digests and two homology bands in others. Molecular weights of these fragments were estimated. Transposon Tn5 was transferred into KR1017, spectinomycin resistant strain of $\underline{R}$. $\underline{japonicum}$ R-271, by conjugation with suicide plasmid vehicle containing Tn5. Transferred Tn5 was stably maintained and specified kanamycin resistance in new host.