During the past decade the pesticidal bacterium Bacillus thuringiensis has been the subject of intensive research. These efforts have yielded considerable data about the complex relationships between the structure, mechanism of action, and genetics of the organism’s pesticidal crystal proteins, and a coherent picture of these relationships is beginning to emerge. Other studies have focused on the ecological role of the B. thuringiensis crystal proteins, their performance in agricultural and other natural settings, and the evolution of resistance mechanisms in target pests. Armed with this knowledge base and with the tools of modern biotechnology, researchers are now reporting promising results in engineering more-useful toxins and formulations, in creating transgenic plants that express pesticidal activity, and in constructing integrated management strategies to insure that these products are utilized with maximum efficiency and benefit.

Bacillus thuringiensis and Its Pesticidal Crystal Proteins

The ways in which plant growth promoting rhizobacteria facilitate the growth of plants are considered and discussed. Both indirect and direct mechanisms of plant growth promotion are dealt with. Th...

The enhancement of plant growth by free-living bacteria

https://www.fabinet.up.ac.za/publication/pdfs/2509-lacey_et_al_2001.pdf

Insect Pathogens as Biological Control Agents: Do They Have a Future?

Bacteria associated with the plant rhizosphere may have beneficial effects on plant growth by providing nutrients and growth factors, or by producing antibiotics and siderophores, which antagonize phytopathogenic fungi and bacteria. There is considerable experimental support for the idea that plant growth promoting bacteria may be used as bio–fertilizers or biological disease control agents to increase agricultural yields. Recent advances in our understanding of the molecular biology of the systems responsible for plant growth stimulation are opening the way to strain improvement by genetic engineering.

Plant Beneficial Bacteria

The purpose of pesticide formulations and recent requirements of pesticide industry are discussed, and the importance of research work on pesticide delivery systems, is pointed out. For this purpose, the microcapsules, as one of the typical controlled release formulations, play an important role. Handling safety of the pesticides is improved considerably by microencapsulation due to hazard and exposure reduction.

Microencapsulation of pesticides and their improved handling safety

Gene replacement mediated by Tn5 sequences was used to integrate the Bacillus thuringiensis subsp. kurstaki HD-1 delta-endotoxin gene (tox) into the chromosome of two corn root-colonizing strains of Pseudomonas fluorescens. A Tn5 transposase deletion element containing the tox gene (delta Tn5-tox) was substituted for a Tn5 element previously present in the P. fluorescens chromosome. Two classes of delta Tn5-tox elements were made. The first class encodes kanamycin resistance in addition to the Tox protein, whereas the second class encodes only the Tox protein. Both classes of delta Tn5-tox elements can no longer transpose, owing to a 324-base-pair deletion in the transposase gene of IS50R, minimizing the potential for horizontal gene transfer of the tox gene to other bacterial species. A frameshift mutation in the transposase gene of IS50L was also constructed to eliminate the possibility of suppression or of a spontaneous reversion at the ochre termination codon that would create an active transposase. Expression of the Tox protein in P. fluorescens strains 112-12 and Ps3732-3-7 was demonstrated by an immunological assay (Western blot) and toxicity against larvae of the tobacco hornworm (Manduca sexta). Images

E J Mayer

Papers

Tn5-mediated integration of the delta-endotoxin gene from Bacillus thuringiensis into the chromosome of root-colonizing pseudomonads.