USE OF RHIZOSPHERE CARBON-SOURCES IN SOLE CARBON SOURCE TESTS TO DISCRIMINATE SOIL MICROBIAL COMMUNITIES

Sole carbon source tests (Biolog(TM)), designed to identify microbial isolates can be used to metabolically fingerprint soil microbial commu nities, although the carbon source profiles were not selected for this purpose, This paper reports on the use of alternative carbon sources not available in the Biolog(TM) GN plates to characterize soil microbi al communities. The carbon sources used are compounds commonly found i n plant root exudates and are, therefore, ecologically more relevant a nd representative of the types of substrates available to microorganis ms in rhizosphere soil. The additional carbon sources tested included various phenolic acids, amino acids, carboxylic acids, long chain alip hatics and carbohydrates. In total, 125 different carbon sources were used to discriminate between soil samples from 9 different sites each with three types of grassland vegetation. The growth curves for differ ent groups of carbon sources were all sigmoidal, but the maximum rate of utilization was faster for carbohydrates, amino acids and carboxyIi c acids than for amides, phenolic and long chain aliphatic acids. Sign ificant discrimination of soil microbial communities between sites, bu t not grassland types, was shown and was more distinct using the exuda te carbon sources than those in the Biolog GN plate. The use of fewer carbon sources which are more ecologically meaningful constitutes a mo re efficient and economical technique. (C) 1997 Elsevier Science B.V.