Some strains of bacterium streptococcus pyogenes secrete poisonous substances called exotoxins. the genes encoding the exotoxins are thought to have originated in bacteriophages, which are viruses that infect bacteria

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scientists have discovered that hiv does not cause aids by the virus's direct effect on the host's immune cells, but rather through the cells' lethal influence on one another. researchers from the gladstone institutes have revealed that hiv does not cause aids by the virus's