Molecular and cultural analysis of seasonal actinomycetes in soils from Artemisia tridentata habitat

in order to understand the temporal dynamics of actinomycete communities of the rhizosphere of the desert plant artemisia tridentata (sagebrush), two complementary methods were used. they were: (1) 16s rdna-based pcr coupled with denaturing gradient gel electrophoresis (dgge), and (2) an agar plate enumeration methodology in which three different media were used to quantify total bacteria, actinomycetes, and fungi. the objective of this research were: (1) to obtain a comprehensive picture of the structure of actinomycete populations, and (2) their dynamics in the rhizosphere of young and old sagebrush plants during two distinct seasons. pcr-dgge analysis showed that actinomycete groups were less diverse in rhizosphere soils collected in winter than in bulk soils. on the other hand, rhizosphere soil of a. tridentata young plants (rsyp) collected in spring showed an enrichment of actinomycete diversity and/or selection of unique actinomycete populations. this was not the case with the actinomycete populations detected in the rhizosphere soil of old plants (rsop) in the same season. in this later case, a shift in the dominant bands on pcr-dgge gels was observed between seasons. finally, the enumeration analysis showed that actinomycete counts tended to be higher in spring, while total bacteria counts were higher in winter. although strong soil type effects were detected, more research in the unexplored environment of sagebrush rhizosphere is necessary.