Abstract
A large number of soil microorganisms, including actinomycetes, eubacteria and fungi were isolated from a sandy agricultural soil. These isolates were characterised according to their ability to produce antibacterial antibiotics, their growth responses to some 43 physiological and nutritional tests, as well as their sensitivity to a range of antibiotics. Using numerical methods it was possible to define nutritional/physiological groups of antibiotic-producing actinomycetes, non-producing actinomycetes, eubacteria and fungi. Resistance to antibiotics was not required in order to gain this discrimination, and, in general, antibiotics were not of value in separating the organisms into groups. Cluster analysis and principal components analysis of the nutritional and physiological test data allowed natural clusters of antibiotic-producing actinomycetes, non-antibiotic-producing actinomycetes, eubacteria and fungi to be identified. Discriminant analysis was used in order to find the most powerful physiological and nutritional characters which allow accurate discrimination between the different groups of organisms. The characters which selected for actinomycetes relative to eubacteria included proline, 0.1% humic acid, nitrate and pH 7.7- 8.0. Proline, asparagine, 0.1% humic acid, and vitamins were among the substrates which allowed antibiotic-producing actinomycetes to be differentiated from non-antibiotic-producing strains. These selective characters were used to design selective media for the isolation of antibiotic-producing actinomycetes. A number of new isolation media were extremely successful in increasing the proportion of antibiotic-producing actinomycetes isolated. A soil perfusion column was evaluated as a possible enrichment system for actinomycetes, allowing the consecutive application of selective parameters. The results were extremely promising, although the system was found to be very complex.