Determination of metabolic activity of streptomycetes in soil microcosms

Two Streptomyces griseus strains were isolated from different soil types. S . griseus CAG 17 strain was isolated from an agricultural area with low org anic matter but rich in phosphorus content and S. griseus 26K strain was is olated from a forest area rich in organic matter with a low phosphorus cont ent. The survival and metabolic activity of these isolates were studied in dynamic sterile soil microcosm systems. The fitness of each isolate was stu died by re-inoculation in a soil type different from its origin. Maximum pe rcentage of germination and respiration rates occurred within the first 48 h after each soil turnover (removal and addition of certain soil volumes). Data suggested that S. griseus CAG17 survived better independently of the s oil type in comparison with S. griseus 26K which sporulated within the firs t 12 h after inoculation. Incubation temperatures did affect the lifecycles in relation to soil type. For example, the lowest temperature tested, 22 d egrees C, was more favourable for extended germination and adaptation in ge neral but revealed lesser spore numbers in the 'foreign' sail environment. Monitoring metabolic activity by estimation of urease, phosphatases and deh ydrogenase-specific activities, between 18 and 35 degrees C incubation temp eratures, was a reliable method for studying the survival and growth of str eptomycete populations in soil. Results also confirmed that respiration rat e and enzyme-specific activity corresponded with spore counts in long-term experiments which were designed for the investigation of survival and growt h of S. griseus CAG17. Under selective pressure by heavy metals, in soil mi crocosm systems, metabolic activity proved a useful tool for the investigat ion of streptomycete activity. These methods could also be applied in agric ultural field studies for monitoring microbial populations under conditions where various 'pollutants' are present in soil samples.