Bacillus thuringiensis toxins with improved activity

Details Bacillus thuringiensis toxins with improved activity Bacillus thuringiensis toxins with improved activity

1998-12-28

2001-10-16

Prouty, Rebecca E. (Department: 1652)

Chemistry: molecular biology and microbiology

Micro-organism, per se ; compositions thereof; proces of...

Bacteria or actinomycetales; media therefor

C536S023100, C536S023400, C536S023710, C435S320100, C435S252330, C435S252340, C435S419000, C424S093200

Reexamination Certificate

active

06303364

ABSTRACT:

BACKGROUND OF THE INVENTION
Insects and other pests cost farmers billions of dollars annually in crop losses and in the expense of keeping these pests tinder control. The losses caused by pests in agricultural production environments include decrease in crop yield, reduced crop quality, and increased harvesting costs.
Coleopterans are an important group of agricultural pests which cause a very large amount of damage each year. Examples of coleopteran pests include alfalfa weevils and corn rootworm.
The alfalfa weevil,
Hyperca postica
, and the closely related Egyptian alfalfa weevil,
Hyperca brunneipennis
, are the most important insect pests of alfalfa grown in the United States, with 2.9 million acres infested in 1984. An annual sum of 20 million dollars is spent to control these pests. The Egyptian alfalfa weevil is the predominant species in the southwestern U.S., where it undergoes aestivation (i.e., hibernation) during the hot summer months. In all other respects, it is identical to the alfalfa weevil, which predominates throughout the rest of the U.S.
The larval stage is the most damaging in the weevil life cycle. By feeding at the alfalfa plant's growing tips, the larvae cause skeletonization of leaves, stunting, reduced plant growth, and, ultimately, reductions in yield. Severe infestations can ruin an entire cutting of hay. The adults, also foliar feeders, cause additional, but less significant, damage.
Approximately 9.3 million acres of U.S. corn are infested with corn rootworm species complex each year. The corn rootworm species complex includes the northern corn rootworm,
Diabrotica barberi
, the southern corn rootworm,
D. undecimpunctata howardi
, and the western corn rootworm,
D. virgifera virgifera
. The soil-dwelling larvae of these Diabrotica species feed on the root of the corn plant, causing lodging. Lodging eventually reduces corn yield and often results in death of the plant. By feeding on cornsilks, the adult beetles reduce pollination and, therefore, detrimentally effect the yield of corn per plant. In addition, members of the genus Diabrotica attack cucurbit crops (cucumbers, melons, squash. etc.) and many vegetable and field crops in commercial production as well as those being grown in home gardens.
Control of corn rootworm has been partially addressed by cultivation methods, such as crop rotation and the application of high phosphate levels to stimulate the growth of an adventitious root system. In addition, an emerging two-year diapause (or overwintering) trait of Northern corn rootworms is disrupting crop rotation in some areas. However, chemical insecticides are relied upon most heavily to guarantee the desired level of control. Insecticides are either banded onto or incorporated into the soil. The major problem associated with the use of chemical insecticides is the development of resistance among the treated insect populations.
Over $250 million worth of insecticides are applied annually to control corn rootworms alone in the United States. Even with insecticide use, rootworms cause over $750 million worth of crop damage each year, making them the most serious corn insect pest in the Midwest.
Damage to plants caused by nematodes is also a prevalent and serious economic problem. Nematodes cause wide-spread and serious damage in many plant species. Many genera of nematodes are known to cause such damage. Plant-parasitic nematodes include members of the Phylum Nematoda, Orders Tylenchida and Dorylaimide. In the Order Tylenchida, the plant-parasitic nematodes are found in two Super Families: Tylenchoidea and Criconematoidea. There are more than 100,000 described species of nematodes.
Chemical pesticides have provided an effective method of pest control; however, the public has become concerned about the amount of residual chemicals that might be found in food, ground water, and the environment. Stringent new restrictions on the use of pesticides and the elimination of some effective pesticides form the marketplace could limit economical and effective options for controlling costly pests. Thus, there is an urgent need to identify pest control methods and compositions which are not harmful to the environment.
Nematicides routinely used for control of plant-parasitic nematodes are rapidly being pulled from the market as concern for environmental safety increases. In the year 2001, Methyl Bromide, a mainstay in the control of such parasites, will no longer be marketed in the United States. Therefore, less harmful control agents are clearly needed.
The use of chemical pesticides to control corn rootworm and other coleopteran pests, as well as nematodes, has several drawbacks. Pesticide use often raises environmental concerns such as contamination of soil and of both surface and underground water supplies. Working with pesticides may also pose hazards to the persons applying them.
The regular use of chemical pesticides for the control of unwanted organisms can select for chemical resistant strains. Chemical resistance occurs in many species of economically important insects and has also occurred in nematodes of sheep, goats, and horses. The regular use of chemical toxins to control unwanted organisms can select for drug-resistant strains. This has occurred in many species of economically important insects and has also occurred in nematodes of sheep, goats, and horses. For example, an accepted methodology for control of nematodes has centered around the drug benzimidazole and its congeners. The use of these drugs on a wide scale has led to many instances of resistance among nematode populations (Prichard, R. K. et al. [1980] “The problem of anthelmintic resistance in nematodes,”
Austr. Vet. J.
56:239-251; Coles, G. C. [1986] “Anthelmintic resistance in sheep,” In
Veterinary Clinics of North America: Food Animal Practice,
Vol 2:4-432 [Herd, R. P., eds.] W. B. Saunders, New York). There are more than 100,000 described species of nematodes. The development of pesticide resistance necessitates a continuing search for new control agents having different modes of action.
At the present time there is a need to have more effective means to control the many coleopterans and nematodes that cause considerable damage to susceptible hosts and crops. Advantageously, such effective means would employ specific biological agents.
The soil microbe
Bacillus thuringiensis
(B.t.) is a Gram-positive, spore-forming bacterium characterized by parasporal crystalline protein inclusions. These inclusions often appear microscopically as distinctively shaped crystals. The proteins can be highly toxic to pests and specific in their toxic activity. Certain B.t. toxin genes have been isolated and sequenced, and recombinant DNA-based B.t. products have been produced and approved for use. In addition, with the use of genetic engineering techniques, new approaches for delivering these B.t. endotoxins to agricultural environments are under development, including the use of plants genetically engineered with endotoxin genes for insect resistance and the use of stabilized intact microbial cells as B.t. endotoxin delivery vehicles (Gaertner, F. H., L. Kim [1988] TIBTECH 6:54-57). Thus, isolated B.t. endotoxin genes are becoming commercially valuable.
Until fairly recently, commercial use of B.t. pesticides has been largely restricted to a narrow range of lepidopteran (caterpillar) pests. Preparations of the spores and crystals of
B. thuringiensis
subsp.
kurstaki
have been used for many years as commercial insecticides for lepidopteran pests. For example,
B. thuringiensis
var.
kurstaki
HD-1 produces a crystalline &dgr;-endotoxin which is toxic to the larvae of a number of lepidopteran insects.
In recent years, however, investigators have discovered B.t. pesticides with specificities for a much broader range of pests. For example, other species of B.t., namely
israelensis
and
morrisoni
(a.k.a.
tenebrionis,
a.k.a. B.t. M- 7, a.k.a. B.t.
san diego
), have been used commercially to control insects of the orders Diptera and Cole

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