USE OF RAPD MARKERS FOR THE DETECTION OF AZOSPIRILLUM STRAINS IN SOIL MICROCOSMS

Probes for the detection of Azospirillum strains were obtained from DNA fragments generated by random ampli®cation of polymorphic DNA (RAPD) and tested to assess their speci®city towards DNA ex- tracted from pure cultures. The most speci®c probe, re- ferred to as a4, produced a hybridization signal only with ampli®ed DNA of A. lipoferum ATCC29731. This strain was inoculated, together with two other Azospir- illum strains, in soil microcosms of di erent complexity and its presence tested with the probe a4. This probe con®rmed its high speci®city with ampli®ed DNA ex- tracted from the soil microcosm and in the presence of other A. lipoferum strains, indicating that the strategy for bacterial detection, based on RAPD markers, is useful for monitoring the presence of a particular strain under environment-like conditions. Other RAPD-de- rived probes, when tested on soil samples, did not show the same level of speci®city as that shown on DNA from pure cultures. This result suggests that some precautions are necessary in the choice of a really speci®c RAPD marker. In a further development of this strategy, the a4 probe was sequenced and two pairs of ``nested'' primers were designed, which enabled a diagnostic polymerase chain reaction from soil samples that was speci®c for the A. lipoferum species.