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Open Access Research article

The liposoluble proteome of Mycoplasma agalactiae: an insight into the minimal protein complement of a bacterial membrane

Carla Cacciotto1, Maria Filippa Addis12, Daniela Pagnozzi2, Bernardo Chessa1, Elisabetta Coradduzza1, Laura Carcangiu1, Sergio Uzzau23, Alberto Alberti1* and Marco Pittau1

  • * Corresponding author: Alberto Alberti alberti@uniss.it

  • † Equal contributors

Author Affiliations

1 Dipartimento di Patologia e Clinica Veterinaria, Università degli Studi di Sassari, Sassari, Italy

2 Porto Conte Ricerche Srl, Tramariglio, Alghero (SS), Italy

3 Dipartimento di Scienze Biomediche, Università degli Studi di Sassari, Sassari, Italy

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BMC Microbiology 2010, 10:225  doi:10.1186/1471-2180-10-225

Published: 25 August 2010

Abstract

Background

Mycoplasmas are the simplest bacteria capable of autonomous replication. Their evolution proceeded from gram-positive bacteria, with the loss of many biosynthetic pathways and of the cell wall. In this work, the liposoluble protein complement of Mycoplasma agalactiae, a minimal bacterial pathogen causing mastitis, polyarthritis, keratoconjunctivitis, and abortion in small ruminants, was subjected to systematic characterization in order to gain insights into its membrane proteome composition.

Results

The selective enrichment for M. agalactiae PG2T liposoluble proteins was accomplished by means of Triton X-114 fractionation. Liposoluble proteins were subjected to 2-D PAGE-MS, leading to the identification of 40 unique proteins and to the generation of a reference 2D map of the M. agalactiae liposoluble proteome. Liposoluble proteins from the type strain PG2 and two field isolates were then compared by means of 2D DIGE, revealing reproducible differences in protein expression among isolates. An in-depth analysis was then performed by GeLC-MS/MS in order to achieve a higher coverage of the liposoluble proteome. Using this approach, a total of 194 unique proteins were identified, corresponding to 26% of all M. agalactiae PG2T genes. A gene ontology analysis and classification for localization and function was also carried out on all protein identifications. Interestingly, the 11.5% of expressed membrane proteins derived from putative horizontal gene transfer events.

Conclusions

This study led to the in-depth systematic characterization of the M. agalactiae liposoluble protein component, providing useful insights into its membrane organization.