Biology · Ch 8 — Microbes in Human Welfare
Microbes as Biocontrol Agents
Microbes as Biocontrol Agents
Biocontrol means using living organisms — in this case, microbes — to control pests and diseases, instead of relying on chemical pesticides. The central idea is that nature already has its own checks and balances; we can harness these natural enemies of pests to protect crops without poisoning the environment.
Chemical pesticides are effective but come with serious downsides. They are often non-biodegradable, meaning they persist in the soil and water for years. They can accumulate in the food chain, harming birds, animals, and even humans. Over time, pests also evolve resistance to these chemicals, forcing farmers to use stronger and stronger doses. Biocontrol agents offer a way around these problems.
The textbook introduces a classic and highly successful example of microbial biocontrol: the use of the bacterium Bacillus thuringiensis (often abbreviated as Bt). This bacterium produces a protein crystal that is toxic to certain insect larvae. When an insect larva eats the bacteria (or the spores containing the crystal), the toxin is activated in the alkaline gut of the insect and kills it. This is a very specific poison — it harms only the target insects, not plants, other animals, or humans.
The toxin produced by Bacillus thuringiensis is a protein. This is the key to how it is used in modern agriculture. Scientists have taken the gene that codes for this toxin and inserted it directly into the DNA of crop plants like cotton and corn. These genetically modified plants are called Bt-cotton, Bt-corn, etc. The plant itself now produces the insect-killing protein, so the farmer does not need to spray the bacteria on the field. This is a direct application of a microbe's natural weapon.
Another important group of microbial biocontrol agents are Trichoderma species. These are free-living fungi that are commonly found in root ecosystems. They are effective biocontrol agents against several plant pathogens. Trichoderma is an effective biocontrol agent against several plant pathogens generally, without the book naming specific crops. They work by competing with the harmful fungi for space and nutrients, and by producing antibiotics that directly kill the pathogens. …