Beyond Biotechnology: The Barren Promise of Genetic Engineering

5 Genes Are Not Immune to Context

Chapter 5 genes are not immune to Context Examples from Bacteria One of the most widespread misconceptions concerning the nature of genes is that they have a defined and fixed function that allows them to operate the same in all organisms and environments. We have a picture of robust genes determining all the characteristics an organism has. And any given gene will do the same thing in a bacterium as in a corn plant or human being. It doesn’t care where it is. The gene bears its set of instructions wherever it goes and strictly carries out its duty. This picture informs genetic engineering. Take a gene from bacteria and put it into a plant, and the plant will produce its own pesticide or become resistant to an herbicide. Since such transgenic plants exist, the proof is evidently in the pudding. Genetic manipulation works; genes are faithful workhorses. But does genetic manipulation work the way we imagine with our schematic pictures? What else may be occurring that doesn’t fit into such a neat mechanistic scheme? It’s somewhat ironic that precisely within the last ten to fifteen years—the period in which genetically modified crops have been developed and commercialized in the United States and some other countries —a wealth of research on genes in relation to environmental effects has been carried out, showing that genes are anything but automatic instruction sets immune to their context. This research has significant implications for the way we assess genetic engineering. Unfortunately, it often seems that the results of this basic research have little effect on the minds and pocketbooks supporting the global drive to manipulate 60 • Genes and Context organisms genetically. In this chapter we discuss some examples of the contextual gene in bacteria. The Interactive Gene With the widespread use of antibiotics in our culture, many bacteria have become resistant. They thrive even when subjected to high doses of antibiotics. As a rule, the resistance comes at a cost, since the resistant bacteria tend to grow slowly. But when they are grown in laboratory cultures, some of these resistant bacteria will experience so-called compensatory mutations—they stay resistant, but change genetically in a way that allows them to grow fast like wild, nonresistant strains. Others mutate back to the wild form and lose their resistance altogether. The question arises whether such mutations (changes in genes or in higher-order genetic structures) are in any way dependent on the environment . The traditional view, rooted deeply in the neo-Darwinian theory of evolution, holds that genes mutate spontaneously and independently of the environment. The classical experiment with bacteria by Salvadore Luria and Max Delbrück in the 1940s gave clear evidence that such spontaneous, milieu-independent mutations exist (Luria and Delbr ück 1943). For decades this experiment (along with other evidence) served as the rock-solid “proof” that genetic mutations, except for extreme cases involving irradiation or exposure to chemical toxins, are not influenced by their environment. But more recent research shows that mutations do in fact arise in response to changing environmental conditions. A group of biologists in Sweden investigated whether the abovementioned compensatory mutations and the reversion to the wild form in bacteria are influenced by the environment (Björkman et al. 2000). They grew antibiotic-resistant bacteria—in the absence of antibiotics —as laboratory cultures (in petri dishes) and also inoculated mice with the same bacteria. The researchers monitored the mutations that occurred in the bacteria in these two different habitats. They found that compensatory mutations occurred in both habitats, but, to their surprise , they discovered that the way the genetic material changed differed significantly depending upon the environment. In the case of streptomycin -resistant bacteria in mice, they found ten cases of identical compensatory mutations within the resistance gene. In contrast, this gene never mutated in the lab-cultured bacteria, where they found fourteen Genes Are Not Immune to Context • 61 compensatory mutations in genes outside the resistance gene. Evidently, the environment had everything to do with what kind of mutations occurred . “Mice are not furry petri dishes,” as the title of a commentary article put it (Bull and Levin 2000). The authors conclude that the mutations are “condition-dependent ”and suggest that some unknown“mutational mechanism”limited the mutations in the mice to a specific part of the resistance gene while also increasing its mutation rate. Whatever the details of cell physiology turn...