Phenotypic variation in Azospirillum brasilense Sp7 does not influence plant growth promotion effects

Victoria Volfson, Sharon Fibach-Paldi, Natalia Soledad Paulucci, Marta Susana Dardanelli, Ofra Matan, Saul Burdman, Yaacov Okon*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


The Azospirillum genus comprises free-living, plant growth-promoting, nitrogen-fixing bacteria found in the rhizosphere of plant roots. Azospirilla are able to promote plant growth mainly through improvement of root development. Bacterial surface components, such as extracellular polysaccharides and proteins, are involved in root colonization. Phase variation - or phenotypic variation - is one of the mechanisms by which microorganisms adapt to environmental changes. This phenomenon is characterized by the presence of a sub-population of the bacteria presenting a different phenotype relative to the major population. In this study we characterized phenotypic variation of Azospirillum brasilense Sp7. When plated on solid media, some A.brasilense colonies were shown to possess a much more mucoid morphology, producing 7.5-8 times more exopolysaccharide with different monosaccharide composition than the parental strain Sp7. The rate of appearance of this kind of variant colonies was 1 in 5000, in agreement with the accepted rate for the phase/phenotypic variation phenomenon. The variants were significantly more resistant to heat and UV-exposure than the parental strain and displayed genomic changes as seen by the different band patterns following ERIC-PCR, BOX-PCR and RAPD analyses. In plant inoculation experiments under greenhouse conditions, with maize, wheat, soybean and peanuts, the EPS overproducing variants performed as similar as the parental strain. Therefore, EPS overproduction did not confer an apparent advantage to A.brasilense in terms of induction of plant growth promotion.

Original languageAmerican English
Pages (from-to)255-262
Number of pages8
JournalSoil Biology and Biochemistry
StatePublished - Dec 2013

Bibliographical note

Funding Information:
N.S.P. is fellows of CONICET-Argentina. M.S.D. is a member of the Research Career of CONICET-Argentina. She was supported by CONICET grant R2397/11 for working at the The Robert H. Smith Faculty of Agriculture, Food and Environment in Rehovot.


  • Azospirillum brasilense
  • Exopolysaccharides
  • Genomic changes
  • Phase variation
  • Phenotypic variation
  • Plant growth promotion


Dive into the research topics of 'Phenotypic variation in Azospirillum brasilense Sp7 does not influence plant growth promotion effects'. Together they form a unique fingerprint.

Cite this