Plasmid Rearrangements and Changes in Cell-Surface Architecture and Social Behavior of Azospirillum brasilense
Azospirilla are well-known plant-beneficial α-proteobacteria. However, they have been isolated not only from a wide range of plant, soil, and water locations, but also from human tissues. Thus, it is not surprising that these highly adaptable bacteria have flexible genomes, composed of several large replicons. In this chapter, experimental data on plasmid plasticity in the type strain A. brasilense Sp7 and in the facultative endophyte A. brasilense Sp245 are discussed. It is shown that certain changes in the primary structure of an 85-MDa plasmid of strain Sp245 were accompanied by alterations in flagellar formation and in bacterial social motility on soft media; e.g., shifts between flagellar-dependent swarming or flagellar-independent microcolonial spreading were noticed. A spontaneous reorganization of 85- and 120-MDa plasmids gave rise to an A. brasilense Sp245 derivative with a novel cell-surface architecture and with altered social motility and biofilm formation. Spontaneous changes in the plasmid profile of A. brasilense Sp7 derivatives encompassing 90- and 115-MDa replicons were concurrent with variations in the colony morphology, cell antigenic structure, swarming, and biofilm formation on abiotic surfaces and plant roots. Such genetic and physiological plasticity of azospirilla is expected to be of significance for their survival in natural environments.
KeywordsWheat Root Azospirillum Brasilense Semisolid Medium Plasmid Profile Nucleotide Residue
All my past and present collaborators are gratefully acknowledged for contributing to the work on azospirilla described in this review. I also thank Dr. Andrei V. Shelud’ko for his help with figures. Research in my lab is currently supported by grants 12-04-00262-a (to E.I. Katsy) and 13-04-01276-a (to L.P. Petrova) from the Russian Foundation for Basic Research.
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