Molecular Tools for Identification and Characterization of Plant Growth Promoting Rhizobacteria with Emphasis in Azospirillum spp.
Azospirillum is considered an important genus among plant growth promoting rhizobacteria (PGPR). After the recent reclassification of Azospirillum irakense to Niveispirillum irakense and Azospirillum amazonense to Nitrospirillum amazonense based on their polyphasic taxonomic characteristics, at present this genus encompasses 15 valid species. In this chapter, the identification and characterization of the genus Azospirillum through genotypic, phenotypic or chemotaxonomic approaches were reviewed. Under the given set of PCR condition, the genus specific primers Azo494-F/Azo756-R were sufficient to differentiate Azospirillum and other closely related genera such as Rhodocista and Skermanella. Along with PCR—denaturing gradient gel electrophoresis (PCR-DGGE) or real-time quantitative PCR (qPCR), the specific primers were useful to detect and identify Azospirillum in a short time no matter pure cultures or environmental samples were used. The minimum detection limit in real-time quantitative PCR analysis is 102 CFU g−1 in the seeded soil sample. Cells of the genus Azospirillum are Gram-stained negative, spiral or rod-shaped and non-spore-forming diazotrophic. Poly-β-hydroxybutyrate granules were observed after few days of incubation. The major fatty acids were C16:0, C16:0 3-OH, C18:1 2-OH, C14:0 3-OH/C16:1 iso I, C16:1ω7c/C16:1ω6c and C18:1ω7c/C18:1ω6c; the predominant polar lipids included phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), diphosphatidylglycerol (DPG), phosphatidyldimethylethanolamine (PDE) and unidentified aminolipid (AL) and phospholipids (PL); the common major respiratory quinone was ubiquinone Q-10 and predominant polyamines were sym-homospermidine and putrescine. These features are also useful to provide bases in the description of members belonging to the genus Azospirillum.
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