Even with genetic modification, resistance may be a nasty problem
Posted 22nd November 2019 by Liv Sewell
Natural resistance to our methods to control pests and weeds is a brand new phenomenon, historically speaking. It only evolved as mankind started to use chemical, and later biotechnological means to control nature. Genetic modification may not be the answer to resistance. Attempts to control pests and weeds by growing GM plants run into the same problem as the application of chemical agents. But still, nature may provide some answers.
It’s hard to avoid resistance
When resistance was first discovered in 1914, researchers hoped that this natural phenomenon would be confined to the inorganic insecticides used at the time. But soon enough they discovered that it also showed up when farmers started to use organic insecticides. Same story with herbicides. Even the strongest weed killer ever developed, Roundup, runs into difficulty because of natural resistance. At first it was thought that Roundup would kill all weeds; the land would then only allow the growth of engineered Roundup resistant crops, such as sold by Monsanto. But this underestimated nature’s resilience. Cotton farmers in the USA now suffer from a Roundup resistant amaranth that developed this property all on its own. It grows very fast and then covers the cotton plants in shade, severely reducing the yield.
GM crops do not escape this fate, as shown by the history of Bt cotton. This is a cotton variety with some DNA of Bacillus Thuringiensis in it. The plantcontains the same pesticide as this bacterium. The purpose is to kill any pests that attack it. But in India and China, resistance to the Bt toxin emerged within 10 years of large-scale cultivation. Resistance can be slowed down (but not prevented) by ‘refuges’, areas with non-Bt crops and plants. These are intended to decrease the chances of two resistant pests mating and producing resistant offspring. But in general, GM as a strategy will run into the same problems as chemical pesticides. As Anne Glover, president-elect of the Royal Society of Edinburgh, puts it: ‘There is a strong pressure for pests to evolve resistance to whatever control pressure we put on them, whether part of a GM strategy or as part of conventional chemical control.’
Resistance to antibiotics is a growing problem
Resistance of bacteria to antibiotics is another instance of the same phenomenon. Resistance can spread through several mechanisms. Firstly, the drug may kill susceptible bacteria, thereby promoting the proportion of non-susceptible bacteria in the population. In the course of time, these may become dominant. Secondly, spontaneous DNA changes may create non-susceptible bacteria. And thirdly, DNA can be swapped between species, thereby rendering resistant a species so far susceptible to the drug.
Bacterial resistance is much enhanced when humans and animals are over-treated with antibiotics, or are treated with broad-spectrum antibiotics where specific medicines could have been used. Bacterial resistance can also result from pharmaceutical effluents not properly cleaned up. In case of resistance, doctors may have to prescribe ever larger amounts of the drugs, which in the end may become ineffective. The problem is growing, as no fundamentally new classes of antibiotics have been discovered since the 1970s. Hospitals may become breeding places for ‘superbugs’ that cannot be controlled any more with available medicines. Estimates show that more than 700,000 people globally now die each year of infections that cannot be cured by antibiotics.
Nature offers us an insight into a possible solution
But how then does nature deal with resistance? After all, nature is characterized by an (albeit dynamic) equilibrium between species. How does nature do this? Recent research shed some light on this question. The researchers studied Atta ants, a species common across the Americas. They cut leaves and carry them to their nests, where they feed them to a fungus. They cannot digest the plant material, but fungi are good decomposers and break it down; the ants then feed on the fungus.
These nests are sometimes attacked by hostile bacteria and fungi. In defence, ants carry in their bodies bacteria that produce powerful antibacterial and antifungal substances. Therefore, there is a tripartite mutualistic relationship between ants, fungi and bacteria. Now British and Italian researchers discovered that the antibiotics produced in the ant nests do not consist of a simple compound, as do our antibiotics, but of a whole series of closely related molecules. Would this prevent antibiotics resistance? Yes, it seems to do so. But it is equally valid to suppose that the ants (and their friendly fungi and bacteria) are engaged in a ‘co-evolutionary arms race’ with their microbial enemies. In order to prevent the hostile organism to develop antibiotics resistance, the tripartite consortium continuously develops new antibiotics from its pool of closely related substances.
Can we accept that the pathogens will win at times?
There is a snag here, if we should wish to copy this mechanism for use by human beings. We humans use antibiotics to kill the pathogens; the ants just contain them. Therefore, the ants don’t always win. Some ant nests are still invaded by fungi in spite of the defence mechanisms. So yes, we may need to accept an evolutionary strategy in the development of our medicines. They need to be part of a cocktail and evolve all the time. This holds for chemical substances and GM strategies alike. But the flipside of this coin is that we cannot always win. We might have to accept that sometimes the pathogens win. Let’s not destroy but contain.
Alle Bruggink is a former research director to DSM and a professor emeritus in industrial organic chemistry and Diederik van der Hoeven is a philosopher and a science journalist. They are both editors at Bio Based Press.
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