Methods for studying phenotypic variation in azospirillum

Phenotypic or phase variation has been demonstrated in many bacteria studied so far. It is an apparently adaptive process enabling bacteria to cope with changing environmental conditions, niche occupation, adaptive versatility, and optimized interaction with host organisms. Phase variation can be caused by genetic as well as epigenetic alteration. In this chapter, we focus on the methodology used to study phenotypic variations in rhizosphere bacteria of the genus Azospirillum. Phase variation can be detected under laboratory conditions, but also in bacteria isolated from the rhizosphere. The awareness of the possible occurrence of phase variation is important for the provision of high quality inoculum. Methods are described for selecting phase variants from cultures, and testing their stability after culture transferring, phenotypic analysis of phase variation includes colony morphology, production of polysaccharides and pigments, and genomic analysis of phase variation including DNA and plasmid profiles. Methods for assessing survival of phase variants and their plant growth promotion abilities in comparison to the parental strain are presented.