Allen Kerr

Dr. Allen Kerr was a University of Adelaide professor and was awarded the Australia Prize in 1990 for his work with plant genetics and biology.

In 1966, Professor Allen Kerr returned to the Waite Agricultural Research Institute in Adelaide, after working in Sri Lanka, and began studies aimed at controlling crown gall disease in fruit trees. In nurseries and orchards in Australia and other fruit-producing regions of the world, it was causing production of more than $100 million annually.

In 1969, one of Professor Kerr's students isolated from a nursery near Adelaide, a strain of Agrobacterium that infected plants without causing cancer-like growth. Experiments showed that the benign strain somehow protected young fruit trees against virulent forms of the same bacterium. When the trees were experimentally inoculated with a mixed culture of the benign and virulent strains, they did not develop crown gall disease.

Professor Kerr's group later showed that the benign bacterium, dubbed strain K84, produces an antibiotic called agrocin 84, which is deadly to pathogenic strains of crown gall bacteria. Strain K84 is itself unaffected, because it possesses a resistance gene that makes it immune to its own antibiotic. The antibiotic is also harmless to most other species of bacteria only virulent strains of Agrobacterium seem to be susceptible. Strain 84 uses the antibiotic to gain a biological advantage over its relatives.

In 1973 Professor Kerr's group released strain K84 in Australia as a biological control agent for crown gall disease. It was highly effective and was subsequently adapted in Europe, Africa, North America and South America. However, in 1973, reports came in from Greece that Strain K84 was losing its effectiveness as a biological control agent for crown gall disease. Greek researchers reported that pathogenic strains of Agrobacterium became resistant to the antibiotic, agrocin 84, when mixed in culture with strain K84.

In a joint project with a research team led by Professor Jeff Schell, of the University of Ghent in Belgium (now of the University of Cologne), Professor Kerr's group determined that Strain K84 was passing its antibiotic resistance gene to pathogenic strains of Agrobacterium on a loop of DNA called a plasmid. Evolution had ensured a pairing of the resistance gene and the antibiotic gene on the same plasmid, so that pathogenic strains acquiring both genes became resistant to biological control.

Professor Kerr decided to use recombinant DNA technology - genetic engineering - to perform surgery on Strain K84. Working with Dr Farrand, of the University of Illinois, Professor Kerr identified a region of DNA that mediates the transfer of the plasmid to other bacteria. Professor Kerr's team deleted the region so that the bacterium retained its ability to synthesise the agrocin antibiotic, but could not pass the resistance gene to other bacteria.

With permission from the Genetic Manipulation Advisory Committee, Professor Kerr performed an experimental field release of the genetically modified bacterium, called strain K1026, in the grounds of the Waite Institute in June 1987. It was only the third recombinant DNA organism to be field-tested anywhere in the world.

In 1988, the NSW Department of Agriculture approved strain K1026 for commercial use as a pesticide, under the trade name No Gall. It can be used anywhere in Australia, but has not been approved for release by countries overseas, where strain K84 Is still used for control. Strain K1026 remains the only recombinant DNA organism released for commercial use anywhere in the world.

No Gall is used to control crown gall by treating disease-free propagation stock. It is applied in an aqueous solution to seeds, seedlings and cuttings before planting and works by protecting wound sites from infection. This new strain is the first genetically engineered micro-organism to be sold live to the public. Its significant commercial potential in major world producers of stone fruits and nuts is highlighted by its user-friendliness, its long shelf-life, and its harmlessness to produce from plants it has treated, as well as to the surrounding environment. Products using the same technology now exist in many forms worldwide, and the product Nogall itself is currently licensed to the NSW company Bio-Care Technology.