SURVIVAL, METABOLIC-ACTIVITY AND CONJUGATIVE INTERACTIONS OF INDIGENOUS AND INTRODUCED STREPTOMYCETE STRAINS IN SOIL MICROCOSMS

The growth and activity of introduced (S. lividans TK24 pIJ673 and S. lividans TK23) and indigenous (S. griseus CAG17) streptomycete strains in soil was studied, under controlled conditions. The effect of envir onmental parameters such as temperature, soil water content and nutrie nt availability on the growth and activity of these strains, was studi ed using a highly dynamic fed-batch soil microcosm system. Using this new system, repeated cycles of active streptomycete growth were achiev ed, allowing long-term investigation of metabolic activity, plasmid st ability and conjugative plasmid transfer. In long-term experiments, re spiration rates and enzyme activity patterns matched the pattern of ge rmination/sporulation cycles of the inoculants. In situ hybridisation, using fluorescently labelled oligonucleotides, also proved the presen ce of metabolically active streptomycete mycelia in sterile soil. Plas mid stability under varying temperatures and selective pressure was st udied using the above system. In both sterile and non sterile amended antibiotic containing soil, no intraspecific transfer of plasmid pIJ67 3 from S. lividans TK24 to S. griseus CAG17 was detected. The soil mic rocosm system used, though, permitted detection of intraspecific conju gative transfer of this plasmid from S. lividans TK24 to S. lividans T K23 in soil.