The total viable bacterial count and the organophosphorous insecticide (quinalphos) resisting bacterial population of the surface soil samples of rice cultivating field was taken. The total heterotrophic bacteria in the soil 81.00 × 10⁷ CFU/g sample was observed, whereas the quinalphos resisting bacterial density was found to be 48.00 × 10⁷ CFU/g, 4.00 × 10⁷ CFU/g at 0.01%, 0.1% pesticide concentrations, respectively. The dominance of gram negative bacterial types was noticed in both total viable bacterial counts, pesticide resisting and degrading bacterial populations. The generic composition of pesticide resisting, degrading bacterial strains showed the higher incidence of Pseudomonas and Bacillus sp. The higher amount of phosphatase enzyme activity was exhibited at 0.1% pesticide concentration. The growth characteristics of pesticide degrading bacteria, strained at different time intervals was also investigated.

During early human civilization, it was realized that pests harm crops and transmit diseases both to human beings and animals. Pesticide is a general term for insecticide, acaricide, rodenticide, molluscicides, herbicides, fungicides and other similarly active compounds. The era of synthetic organic pesticides started around 1940. At present, there are more than 10,000 different pesticides, used to kill various kinds of pests. Pesticides are broadly classified into several types according to their general chemical nature (Sharma, 2004). The annual production of pesticides increased from the green revolution period from £6,000 mn to over £24,000 mn. In the current era, where pesticides play a vital role in day-to-day life, large quantities of pesticides, some of which are highly toxic, are being used regularly by industries, consumers, and farmers, to enhance agricultural productivity. Pesticide manufacturing industries increased across the world during the past three decades. Extensive and improper use of chemicals pose greater risk to plants, animals and human beings, which has been reviewed from time to time. One of the major problems besides toxicity and carcinogenicity is their long persistence, which amplifies the toxicity and health problems in the area of contamination. There are chemical and physical factors that influence the fate of pesticides but the least predictable detoxification is usually caused by microorganisms. A number of aerobic and anaerobic microbes, isolated from soil, water and other habitats have been known for their degrading capability towards various pesticides and have been proved highly potential for partial or complete degradation of pesticides (Babu et al., 1998).

Soil samples from the paddy field were collected to take the total viable counts of pesticide-resisting bacterial population. The paddy field was sprayed with quinalphos pesticide during earlier cultivation period. Soil samples were collected from different areas of the field by using sterile scalpel and these soil samples were placed in sterile polythene bags. After collection of these soil samples, they were placed inside the ice box and brought to the lab immediately for microbiological analysis. The time taken for the collection of samples and processing never exceeded 2 h (Kannan, 2003).

Environmental Sciences Journal, Microbial Degradation, Organophosphorous Insecticide, Soil Bacteria, Green Revolution Period, Agricultural Productivity, Colony Forming Units, Microbial Strains, Microorganisms, Heterotrophic Bacterial Density, Heterotrophic Bacterial Genera, Agricultural Soil, Bacterial Communities.