Genetically Modified Organisms

Some of us joined this Academy when Carlos Chagas was president. Upon meeting him for the first time, we knew that we were in the presence of a person of great vision, enormous integrity, and unquestioned dedication to science. His dedication to science had two foundations. One was his inherent fascination with the natural world. The second was his conviction that science could advance human welfare. Ever since last summer I have been thinking of how interested he would have been in the extraordinary scientific news coming from his beloved Brazil. On July 13, 2000, the cover of Nature Magazine displayed an insect, a leaf hopper, sitting on an orange or grapefruit. Inside, was a paper reporting the entire genome sequence, more than 2 million 600 base pairs (2,679,305), of the bacterium Xylella fastidiosa.' The many authors were from 34 different laboratories and a bioinformatics center in the State of Sao Paulo, Brazil. For part of its life cycle, Xylellu fastidiosa lives in the leaf hopper's gut. From there, it is delivered into the xylem of a plant by the feeding leaf hopper where it multiplies and causes chlorosis, the loss of chlorophyll by citrus trees. The tree produces useless fruit prematurely with consequent loss of the crop. Relatives of this bacterium cause diseases in coffee, nuts, fruits including grapes, and other important plants. Xylella is a major problem for Brazil which produces a third of the worlds oranges and half of the worlds orange juice concentrate. Remarkably, at least 83 Xylella genes are derived from bacteriophage genomes ... the viruses that infect bacteria. Among these are genes associated with virulence in other bacteria infecting other plants. Thus, the bacteriophage have been the agents of gene transfer between species.