Merging Microbes Precede Gene Therapy by Millions of Years
Nature Magazine reports that "The parasite that causes sleeping sickness once swallowed a plant, say researchers. They have found plant-like genes in the organism, suggesting that drugs based on herbicides might be able to kill it."

At least as interesting however, is the last paragraph which says "The finding shows how easy it is for microbes to mix and match genes from different sources for different uses, says evolutionary biologist Miklos Muller of Rockefeller University in New York."

So releasing altered genes into the biosphere not only makes it possible for unpredicted transfer to other life forms, given the engineering of living things, it starts to look pretty well certain.