Ice-Minus Bacteria

In cold weather conditions, frost settles on plants and can cause a great deal of damage. The agricultural industry suffers heavy losses every year due to frost-damaged crops. Researchers hope that spraying ice-minus bacteria on a wide-scale of plants may help stave off the annual havoc caused by frosty conditions. Environmentalists, on the other hand, question the effect this might have on the ecosystem.

The ice-minus bacterium is a mutant strain of the common wild-type bacteria Pseudomonas syringae (P. syringae). The wild-type P. syringae bacterium is known as ice-plus bacteria. It contains a surface protein in its outer cell wall that helps with frost formation, hence the name ice-plus. In the case of the mutant P. syringae, the frost-facilitating surface protein is missing, so these types of bacteria cannot facilitate frost formation and are therefore known as ice-minus bacteria. Both ice-minus bacteria and ice-plus bacteria are found in nature. However, the ice-minus bacteria to be used for spraying crops are made on a large scale using recombinant DNA technology.

In the 1970s, Stephen Lindow, a graduate student of the University of Wisconsin-Madison, discovered that the Pseudomonas syringae (P. syringae) bacteria played a role in frost formation in plants. He was working on research begun by the U.S. Department of Agriculture researcher, Dr. Hall Hoppe.

Dr. Hoppe, in 1961, had been testing fungal infection in corn. He dried infected corn leaves and crushed them into powder. Then he sprinkled the powder on corn plants. The result was that the crops that had been sprinkled with the powder suffered frost damage while the plants that had not been sprinkled with the powder remained well and healthy. This puzzled researchers until Stephen Lindow discovered the presence of ice-plus bacteria in the powdered leaves.

Stephen Lindow, on carrying out further research, discovered the ice-minus strain of bacterium in 1977. Later he discovered a way of recreating these ice-minus bacteria using restriction enzymes and recombinant DNA technology.

In 1987, in a move roundly criticized by environmentalists, the U.S. government allowed Advanced Genetic Sciences to field test ice-minus bacteria on a strawberry field. This field test and subsequent ones showed that spraying ice-minus bacteria on crops could be an efficient way of saving crops from frost. While this may seem like a boon to farmers, the concerns of the environmentalists have to be looked at. What will be the long-term effects of introducing the genetically engineered ice-minus bacteria into the ecosystem? In nature, the ice-plus and ice-minus strains balance each other, but an abundance of the genetically engineered ice-minus strain might have negative consequences. For instance, the bacteria may prevent cloud formations; the ice nucleating proteins in ice-plus bacteria help create ice crystals that lead to cloud formations.

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