Ice-minus bacteria is a common name given to a variant of the common bacterium Pseudomonas syringae (P. syringae). This strain of P. syringae lacks the ability to produce a certain surface protein, usually found on wild-type P. syringae. The "ice-plus" protein (INA protein, "Ice nucleation-active" protein) found on the outer bacterial cell wall acts as the nucleating centers for ice crystals.[1] This facilitates ice formation, hence the designation "ice-plus". The ice-minus variant of P. syringae is a mutant, lacking the gene responsible for ice-nucleating surface protein production. This lack of surface protein provides a less favorable environment for ice formation. Both strains of P. syringae occur naturally, but recombinant DNA technology has allowed for the synthetic removal or alteration of specific genes, enabling the ice-minus strain to be created from the ice-plus strain in the lab.
The ice nucleating nature of P. syringae incites frost development, freezing the buds of the plant and destroying the occurring crop. The introduction of an ice-minus strain of P. syringae to the surface of plants would reduce the amount of ice nucleate present, rendering higher crop yields. The recombinant form was developed as a commercial product known as Frostban. Field-testing of Frostban in 1987 was the first release of a genetically modified organism into the environment. The testing was very controversial and drove the formation of US biotechnology policy. Frostban was never marketed.