Viability of indigenous soil bacteria assayed by respiratory activity and growth

Comparison of methods used to determine the amount of viable bacteria in soil shows that microcolony and 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) reduction assays result in comparable numbers and plate counts result in less numbers due to cell clumping or reduced culturability. The microcolony assay, involving single-cell observations, is effective in measuring viable cells in soil. Number of culturable and viable bacteria increases in the prewetted soil and decreases in predried soil.