Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Desoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III

Abstract

Biologists have long attempted by chemical means to induce in higher organisms predictable and specific changes which thereafter could be transmitted in series as hereditary characters. Among microorganisms the most striking example of inheritable and specific alterations in cell structure and function that can be experimentally induced and are reproducible under well defined and adequately controlled conditions is the transformation of specific types of Pneumococcus. This phenomenon was first described by Griffith (1) who succeeded in transforming an attenuated and non-encapsulated (R) variant derived from one specific type into fully encapsulated and virulent (S) cells of a heterologous specific type. A typical instance will suffice to illustrate the techniques originally used and serve to indicate the wide variety of transformations that are possible within the limits of this bacterial species.Griffith found that mice injected subcutaneously with a small amount of a living R culture derived from Pneumococcus Type II together with a large inoculum of heat-killed Type III (S) cells frequently succumbed to infection, and that the heart's blood of these animals yielded Type III pneumococci in pure culture. The fact that the R strain was avirulent and incapable by itself of causing fatal bacteremia and the additional fact that the heated suspension of Type III cells contained no viable organisms brought convincing evidence that the R forms growing under these conditions had newly acquired the capsular structure and biological specificity of Type III pneumococci.The original observations of Griffith were later confirmed by Neufeld and Levinthal (2), and by Baurhenn (3) abroad, and by Dawson (4) in this laboratory. Subsequently Dawson and Sia (5) succeeded in inducing transformation in vitro. This they accomplished by growing R cells in a fluid medium containing anti-R serum and heat-killed encapsulated S cells. They showed that in the test tube as in the animal body transformation can be selectively induced, depending on the type specificity of the S cells used in the reaction system. Later, Alloway (6) was able to cause

DNA triple helices: Biological consequences and therapeutic potential

“…Friedrich Miescher discovered DNA in 1868, yet it took more than 70 years to demonstrate that it is the molecule that carries genetic information [1]. Once this was realized, tremendous effort has been made to better understand both the structure and function of DNA.…”

Bacteria are small but not stupid: cognition, natural genetic engineering and socio-bacteriology

“…I was far from the only microbiologist to receive this message. Molecular genetics began with the study of transformation in gram-positive bacteria -the ability of bacterial cells to incorporate information from exogenous DNA -and this was where we first learned about DNA as hereditary material (Avery et al, 1944). My thesis advisor, Bill Hayes, established his reputation by showing how autonomous plasmids can promote DNA transfer between bacterial cells (see Hayes, 1968).…”

Os Experimentos De Griffith No Ensino De Biologia: A Transposição Didática Do Conceito De Transformação Nos Livros Didáticos

“…Em trabalhos posteriores, a substância responsável pela transformação foi isolada e identificada como sendo o DNA (AVERY et al, 1944). Detalhes acerca da proposta do DNA como material genético estão sendo investigados em um estudo mais aprofundado por nós realizado.…”

“…Para Griffith o componente do extrato celular responsável pela transformação de um tipo em outro era uma proteína. Porém, convém lembrar que, na época em que os experimentos de Griffith sobre transformação bacteriana foram realizados não se sabia a natureza do material genético, que somente foi conhecida em trabalhos posteriores (AVERY et al, 1944). Segundo Gardner e Snustad (1986), Agora sabemos que o segmento de DNA no cromossomo dos pneumococos que carrega a informação genética que especifica a síntese da cápsula do Tipo III é fisicamente integrado no cromossomo da célula receptora da variante R do Tipo II por um processo específico de recombinação que ocorre durante a transformação (p.63).…”