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Chapter 31 : A Love Affair with Streptomyces Genetics
One of the Ph.D. topics on offer for the author at the Cambridge University was the actinomycete Streptomyces. In the pneumococcus, Escherichia coli and Salmonella typhimurium, incomplete genomes were transferred from donor to recipient strains by one of three bizarre processes (transformation, conjugation, and transduction) to yield incomplete zygotes, whereas fungi and higher organisms had life cycles, including a complete diploid stage and meiosis. Lewis Frost gave the author some Streptomyces cultures. The author streaked them out and chose one that produced a striking blue pigment. He set about isolating auxotrophic mutants from this Streptomyces coelicolor strain in order to look for genetic recombination in the way it was done for E. coli. By the early 1950s, few microbiologists regarded the actinomycetes as fungi, but many still thought of them as intermediate between fungi and bacteria. For Streptomyces there were biochemical pointers to a bacterial affinity, but their cellular architecture was unclear. In the 1970s, the author's research group added artificial protoplast fusion to natural, plasmid-mediated conjugation as a means of doing Streptomyces genetics and then, much more important, the ability to transform protoplasts with plasmid or bacteriophage DNA, thus ushering in the in vitro years of gene cloning, which really put Streptomyces genetics on the map. Soon, numerous antibiotic resistance genes had been isolated, and basic aspects of gene expression worked out. They could manipulate the production of antibiotics by streptomycetes, which had enormous potential importance for the emergence of biotechnology in the pharmaceutical industry.