Full Length Research Paper

Population dynamics of soil microbes and diversity of Bacillus thuringiensis in agricultural and botanic garden soils of India

Tushar Kanti Dangar, Y. Kishore Babu and Jyotirmayee Das

Microbiology Laboratory, Division of Crop Production, Central Rice Research Institute, Cuttack 753006, Orissa, India.

*Corresponding author. E-mail: dangartk@rediffmail.com. Tel: 91-0671-2367768-783 Ext. 207. Fax: 91-0671-2367663.

Accepted 18 August, 2008

   Abstract

Different microbial guilds of three rice fields (aerobic (dry or wet) laterite and red sandy, and anaerobic (flooded), clay-loam), a botanical garden (wet, aerobic, humus) and a sorghum (dry, aerobic, sandy) soil were investigated. Population (x10⁶ cfu/g dr. soil) of the aerobic (3.8 - 26.2) and anaerobic (0.91 - 13.6) heterotrophic, aerobic (1.1 - 3.7) and anaerobic (0.8 - 1.3) spore forming, Gram (-)ve (0.3 - 0.7), phosphate solubilizing (0.01 - 0.06), asymbiotic N₂-fixing (0.26 - 0.88), sulfur oxidizing (0.13 - 0.75), sulfate reducing (0.01 - 0.1), nitrifying (0.1 - 0.23) and denitrifying (0.04 - 0.25) bacteria; actinomycetes (0.01x10⁴ cfu/g dr. soil), fungi (0.01 - 0.05x10⁵ cfu/g dr. soils) and Bacillus thuringiensis (Bt) (0.13-0.25x10⁶ cfu/g dr. soil) population were variable in different soils. Nevertheless, proportions of Bt in relation to spore forming bacteria were comparable (index (5-9) x10^-4) and they produced either monotypic (bipyramidal or spherical) or heterotypic (polymorphic-bipyramidal or bipyramidal-rhomboidal) crystals although the bipyramidal crystal producing Bt were predominant in the soils. The bipyramidal crystal producing Bt were diverse in different ecologies, resistant to penicillin group of antibiotics and tolerated 5 - 6% NaCl. Phenotypic characters allowed to group the Bt isolates of botanic garden as B. thuringiensis subsp. coreanensis and as B. thuringiensis subsp. thompsoni/coreanensis, sorghum fields as B. thuringiensis subsp. finitimus and but those of rice fields as B. thuringiensis subsp. thuringiensis/ shandongiensis, finitimus and thompsoni/coreanensis. The isolates produced 25.78, 25.78, 86.26, 24.73, 68.0, 26.8 and 26.8 kDa proteins and equivalent to Cyt, Cry5 and Cry2 toxins effective against the insects of Diptera and Lepidoptera/Coleoptera.

Key words: Microbial diversity, stress tolerance, Bacillus thuringiensis, rice, soil.