Spontaneous Super-Swarming Derivatives of Azospirillum brasilense Sp245 have Different DNA Profiles and Behavior in the Presence of Various Nitrogen Sources

Abstract

Azospirillum brasilense swims in liquid environments and swarms in semisolid media. Five variants of A. brasilense Sp245, Sp245.P1-Sp245.P5, which swarmed faster than Sp245 in a semisolid malate-salt medium, have been isolated. In Sp245.P1-Sp245.P4, a new megaplasmid was revealed instead of an indigenous 85-MDa plasmid (p85). By polymerase chain reactions (PCR) with primers to the segments of p85 important for proper bacterial motility/ flagellation and for dissimilatory nitrite and NO reduction, that DNA of p85 was found retained by all the variants. In ERIC-and RAPD-PCR, microdiversity between the total DNAs of Sp245 and its variants was detected. Interstrain differences in growth characteristics in liquid peptonesuccinate-salt medium with KNO 3 or KNO 2 and in KNO 2 production/consumption were revealed. Although all the variants swam and swarmed faster than Sp245 in the medium supplemented with NH 4 Cl or KNO 3 , not all of them could do so in MPSS with KNO 2 .