放線菌の遺伝子操作(組換え微生物の農業利用-野外での利用を中心にして-)

抄録

Streptomyces are gram-positive soil bacteria that undergo a complex cycle of morphological differentiation. Their genome consists of single circular chromosomes whose size is approximately 10^4 kb. As they produce various kinds of antibiotics, they have attracted the attentions of researchers for many years. Recently, recombinant DNA techniques in Streptomyces have been developed and gene cloning has made it possible to carry out the experiments with Streptomyces which were impossible before. In the first part of this article, detailed accounts on the cloning experiments are given. The factors which should be considered in selecting host strains and vectors are listed. Genome fluidity of streptomycetes has been studied extensively. Most of the Streptomyces plasmids possess a transfer function, which contributes to the exchange of genetic information between strains. Some important phenotypic traits can be lost due to extensive deletions including structural genes for phenotypic traits studied along with considerable amplification of genome segments. In studying the mechanism of integration of the plasmid SCP1 into the S. coelicolor chromosome, a sequence of about 2kb was found to be present both on the S. coelicolor chromosome and on SCP1. This DNA segment was found to be transposable. The role of genome fluidity in the ecology, taxonomy and evolution of Streptomyces is discussed.