MICROBIAL BIOTECHNOLOGY: SCOPE, TECHNIQUES CONTD.
CONTROL OF PATHOGENIC BACTERIA, FUNGI,AND PARASITIC NEMATODES
The cell walls of many plant pests, such as insects and fungi, contain chitin
(poly-N-acetylglucosamine) as a major structural component. Many bacteria (e.g., species of Serratia, Streptomyces, and Vibrio) produce chitin degrading enzymes (chitinases). The control of some fungal diseases by such bacteria has been correlated with the production of chitinases. Genes
encoding chitinases from several different soil bacteria have been cloned
into Pseudomonas fluorescens,an efficient colonizer of plant roots.The effectiveness of these recombinant strains in controlling fungal disease is not yet known.
BACILLUS SUBTILIS STRAINS AS BROAD-SPECTRUM MICROBIAL PESTICIDES
Selected B. subtilis strains are widely accepted as broad-spectrum microbial pesticides. Strains of the common soil bacterium B. subtilis secrete a formidable array of compounds, which together display antifungal, antibacterial, and even insecticidal activities. These include two different classes of lipopeptides designated iturins and plipastatins; a surfactant called surfactin; 2,3-dihydroxybenzoylglycine, an iron-chelating agent; and potent proteases with broad specificity. Iturin lipopeptides consist of oneβ-amino fatty acid and seven α-amino acids, whereas surfactins and plipastatins consist of oneβ-hydroxy fatty acid and seven and 10α-amino acids, respectively. Large amounts of a B. subtilis strain capable of producing this potent mixture of products can be obtained by solid-state fermentation with soybean curd residue as substrate. Under these cultivation conditions, the cells produce greatly elevated levels of the lipopeptides. When the mixture of cells and metabolites obtained by the solid-state fermentation is directly applied to soil, it suppresses the growth of various plant pathogens.
RESISTANCE TO VIRAL DISEASES:
Plant virus diseases are difficult to control. Research in the mid-1980s showed that transgenic tobacco expressing the coat protein (capsid) gene of tobacco mosaic virus (TMV) is resistant to TMV, and it was speculated that the resistance is the result of the interference with virus uncoating by the expressed coat protein. Similar coat protein transgene-mediated protection was reported for a number of other related plant RNA viruses, TMV, cucumber mosaic virus, alfalfa mosaic virus, and several potato viruses. The protection is now known to be the result of RNA silencing, a cell-based sequence specific post transcriptional RNA degradation system that is programmed by the transgene-encoded RNA sequence. In Hawaii, papaya ranks as the second most important fruit crop. This crop was subject to severe damage caused by papaya ringspot virus (PRSV). The introduction in 1998 of transgenic papaya cultivars with a transgene that expressed a PRSV coat protein saved the Hawaiian papaya industry. In recent years, transgenic plants have been engineered with a variety of other sequences, encoding either viral proteins or RNAs that confer virus resistance.
Please Refer This Links To:
Msc Microbiology, TU .
Assistant Professor In Pokhara University, Pokhara Bigyan Thata Prabidhi Campus, PNC, LA, NA.