USE OF RANDOM AMPLIFIED POLYMORPHIC DNA MARKERS FOR THE DETECTION OF AZOSPIRILLUM STRAINS IN SOIL MICROCOSMS

Probes for the detection of Azospirillum strains were obtained from DN A fragments generated by random amplification of polymorphic DNA (RAPD ) and tested to assess their specificity towards DNA extracted from pu re cultures. The most specific probe, referred to as alpha 4, produced a hybridization signal only with amplified DNA of A. lipoferum ATCC29 731. This strain was inoculated, together with two other Azospirillum strains, in soil microcosms of different complexity and its presence t ested with the probe alpha 4. This probe confirmed its high specificit y with amplified DNA extracted from the soil microcosm and in the pres ence of other A. lipoferum strains, indicating that the strategy for b acterial detection, based on RAPD markers, is useful for monitoring th e presence of a particular strain under environment-like conditions. O ther RAPD-derived probes, when tested on soil samples, did not show th e same level of specificity as that shown on DNA from pure cultures. T his result suggests that some precautions are necessary in the choice of a really specific RAPD marker. In a further development of this str ategy, the alpha 4 probe was sequenced and two pairs of ''nested'' pri mers were designed, which enabled a diagnostic polymerase chain reacti on from soil samples that was specific for the A. lipoferum species.