IMPROVED SOIL DISPERSION PROCEDURES FOR TOTAL BACTERIAL COUNTS, EXTRACTION OF INDIGENOUS BACTERIA AND CELL-SURVIVAL

The effects of different soil dispersion procedures for enumeration an d extraction of indigenous soil bacteria were investigated. Increased counts and extraction efficiency were obtained with pyrophosphate inst ead of water as dispersion liquid. When physical dispersion was conduc ted in the Waring blender, the effect of container volume and number o f dispersions on extraction efficiency and bacterial counts was shown. An extraction efficiency of 70-80% of soil bacteria was obtained by r epeated extractions, compared to 25% with one extraction. Cell damage by different container volumes was investigated by measuring the physi cal cell integrity and viability of pure cultures of Escherichia coli and Bacillus subtilis when dispersed in slurries of gamma-sterilized s oil. Nearly identical decay rates were observed with the different War ing blender containers. Separation of soil particles and bacteria by N ycodenz density gradient centrifugation facilitated almost complete se paration of structurally intact cells and soil particles. Enzymatic cl eavage and chemical oxidation of soil polysaccharides by periodate tre atment did not increase the extraction efficiency.