Understanding Bacillus Thuringiensis (Bt)

in Issue 32 by

Do you use chemicals on your vegetables?” is a question that the farmer selling directly to the customer is likely to hear. Often the farmer answers, “Only when necessary” or “No, I am organic”. For questions like this, it is hard to give an accurate answer because most farmers whether organic or not, use some form of chemicals on their farms. Some farmers that are strictly organic must avoid certain chemicals but are still likely using some “natural” forms that are considered non-toxic.

The scientific definition of a chemical is any basic substance that is used in or produced by a  reaction involving changes to atoms or molecules.It is evident then, that chemicals include many things which may be harmful or helpful.Chemicals come in many forms. They can kill instantly, be completely safe – even beneficial to our health, or slowly cause damage to our bodies over the long-term. The inherent properties, method of use, concentration, and other factors determine the effect on the human body whether dangerous or not. For example, vinegar, bleach, sulfuric acid, glyphosate, and cyanide are all chemicals and have very different effects on our body and on living things in the environment. A better question then is for the customer to ask the farmer, “What types of chemicals do you use?”

I find it a little alarming that sometimes farmers are not able to specifically answer that question very well in a way that gives the customer an informed understanding of the subject. What is used to grow the food we are eating is important to all of us.It is important for the farmer and the customer to know about types of chemicals used in agriculture so wise decisions can be made about the food we grow and eat.

With that goal in mind, I would like to discuss Bacillus Thuringiensis (Bt) which is used in both organic and conventional farming. Bt is actually a specific species of bacteria that is found naturally in the soil. It can be classified as one of a group of substances called biopesticides or biologicals. Biopesticides are certain types of pesticides derived from plants, bacteria, fungi, animals, or certain minerals. The term biological means that they are the product of natural chemical synthesis usually coming from a living substance. Because something is classified as a biological in itselfdoesn’t indicate whether it is toxic to the human body; it only indicates that it comes from a naturally occurring source. Certain plants, for example, can contain strong poisons that could kill you very quickly. Therefore, it depends on an analysis of the specific components of the biological to determine its toxic or non-toxic properties.

Based on research up to this point, Bt has been observed to contain components that are non-toxic to the human body when used in sprays because it does not penetrate the cellular wall of the plant cell, but deadly to certain types of insects.This bacteria produces a protein that, when inside the intestines of certain types of caterpillars or worms, forms protein molecules that cause holes to form in the intestinal lining of the insect. The worms then disintegrate from the inside out and are soon shriveled and black in the garden. Bt bacteria is widely accepted as a non-toxic spray and allowed even in some of the strictest organic farms. It is applied as a liquid spray or a dust to the leaves of the plants where the worms are located. Since it contains a living bacteria in the ingredients, the Bt concentrate needs to be kept in a sealed container out of intense heat and light. It is usually able to be found for sale in farm chemical supply stores.

Our discussion of Bt would not be complete without mentioning the topic for which this bacteria is infamously known for. This is the name given to a genetically modified (GM) trait common in certain corn varieties that are widely grown in the United States. Capitalizing on the action of the proteins produced by this Bt bacteria species, scientists found a way to take the DNA in this bacteria cell that is specifically responsible for creating the deadly insect killer molecule and insert that DNA into a cell taken from a corn plant. The cell is then multiplied in a laboratory with the result that after several steps, full size plants are able to be produced. These plants can be grown to produce corn seeds that contain genetic information that automatically produces the same protein originally produced by the Bt bacteria in every cell of the corn plant. The result of this technology has been incredible. Now with every cell of the plant containing protein molecules that are toxic to caterpillars and worms, the two greatest pests of corn, (corn borer and corn earworm) are almost completely controlled without sprays. Now every time the eggs of these pests hatch on the corn plant, the larvae immediately have only a food source that is almost 100% deadly to them. There is however a very small number of these pests that somehow are resistant to the Bt toxin. Because of this, it is a concern that at some point in the future this technology will no longer be effective as an insect control if a population of insects resistant to Bt is eventually able to dominate.

In conclusion, Bt is the name of two things. Both have a deadly effect on the target insect pests. However, the similarities stop there. One is a biopesticide containing a live bacteria used in both organic and conventional agriculture, and the other is a modified genetic trait created within a plant to manufacture certain proteins within the plant. One is sprayed in small quantities on the exterior of the crops and the other is genetically produced within every plant cell. Both are said to be safe for consumption but to date there hasn’t been comprehensive research to determine the long-term effects of the bacteria or the specific proteins after they are consumed. Research is needed to determine how these protein molecules are absorbed in the digestive system and the short term and long term effects on the body.