In situ identification of plant-invasive bacteria with MALDI-TOF mass spectrometry

Dominik Ziegler, Anna Mariotti, Valentin Pflüger, Maged Saad, Guido Vogel, Mauro Tonolla, Xavier Perret*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

36 Scopus citations


Rhizobia form a disparate collection of soil bacteria capable of reducing atmospheric nitrogen in symbiosis with legumes. The study of rhizobial populations in nature involves the collection of large numbers of nodules found on roots or stems of legumes, and the subsequent typing of nodule bacteria. To avoid the time-consuming steps of isolating and cultivating nodule bacteria prior to genotyping, a protocol of strain identification based on the comparison of MALDI-TOF MS spectra was established. In this procedure, plant nodules were considered as natural bioreactors that amplify clonal populations of nitrogen-fixing bacteroids. Following a simple isolation procedure, bacteroids were fingerprinted by analysing biomarker cellular proteins of 3 to 13 kDa using Matrix Assisted Laser Desorption/Ionization Time of Flight (MALDI-TOF) mass spectrometry. In total, bacteroids of more than 1,200 nodules collected from roots of three legumes of the Phaseoleae tribe (cowpea, soybean or siratro) were examined. Plants were inoculated with pure cultures of a slow-growing Bradyrhizobium japonicum strain G49, or either of two closely related and fast-growing Sinorhizobium fredii strains NGR234 and USDA257, or with mixed inoculants. In the fully automatic mode, correct identification of bacteroids was obtained for >97% of the nodules, and reached 100% with a minimal manual input in processing of spectra. These results showed that MALDI-TOF MS is a powerful tool for the identification of intracellular bacteria taken directly from plant tissues.

Original languageEnglish (US)
Article numbere37189
JournalPloS one
Issue number5
StatePublished - May 17 2012
Externally publishedYes

Bibliographical note

Funding Information:
Co-authors Valentin Pflüger and Guido Vogel are employees of Marbitrec AG. Dominik Ziegler is a PhD student in Geneva whose research is partially funded by Mabritec AG. There are no patents or products in development to declare. This does not alter the authors' adherence to all of the PLoS ONE policies on sharing data and materials.

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)
  • Agricultural and Biological Sciences(all)
  • General


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