Cultivation of a single crop on a given tract of land leads eventually to decreased yields. One reason for this is that harmful bacterial phytopathogens, organisms parasitic on plant hosts, increase in the soil surrounding plant roots. The problem can be cured by crop rotation, denying the pathogens a suitable host for seeds with fluorescent pseudomonads. Similar treatment of sugar beets, cotton, and potatoes has had similar results.
These improvements in crop yields through the application of Pseudomonas fluorescents suggest that agriculture could benefit from the use of bacteria genetically altered for specific purposes. For example, a form of phytopathogen altered to remove its harmful properties could be released into the environment in quantities favorable to its competing with and to cause frost damage, thereby rendering it safer than the phytopathogen from which it was derived.
Some proponents have gone further and suggest that genetic alteration techniques could create organisms with totally new combinations of desirable traits not found in nature. For example, genes responsible for production of insecticidal compounds have been transposed from other bacteria into pseudomonads that colonize corn roots. Experiments of this kind are difficult of opponents and create a climate in which such research can go forward without undue impediment.
What this question is testing
Topic
The author is walking through how some bacteria help crops — first naturally, then through genetic engineering — and laying out the debate over deliberately releasing altered bacteria.
Framework
Present Debate. The author isn't taking sides directly; they're presenting both arguments and a hopeful direction.
Main Point
Here's the simpler version: some natural soil bacteria help crops by crowding out the bacteria that hurt them. Treating seeds with these helpful bacteria has already boosted yields. Some scientists want to take this further: alter bacteria genetically to do new helpful things, like a frost-damage version of P. syringae with the harmful gene removed. Critics worry about releasing engineered bugs into nature. Supporters argue that since the altered version is just a stripped-down version of an existing strain, it's actually safer than the original.
P1: Helpful bacteria, naturally
Continuously farming the same crop builds up bad bacteria. Rotation helps, but even without rotation, soil eventually develops a population of good bacteria like P. fluorescents that crowds out the bad ones. Coating seeds with these good bacteria has boosted yields significantly across several crops.
P2: Helpful bacteria, engineered
If natural bacteria can do this, why not engineer custom ones? Proponents' lead example: take P. syringae, which causes frost damage, remove the gene that causes the damage, and release the harmless version to crowd out the harmful one. Critics worry that releasing engineered bacteria could backfire. Proponents say the altered version is safer than what's already out there, since it's missing the harmful gene.
P3: Even more ambitious projects
Some go further — combining genes from different bacteria to create new traits, like making a corn-root bacterium that produces insecticide. These engineered bacteria are tricky to develop and may not survive in real soil. Still, the supporters are optimistic and hope risk assessments will quiet the critics so the research can continue.
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