Proteomics Investigation of Pseudomonas Fluorescens Chromogenic Strains: Insight in Blue-Mozzarella

Introduction and Objectives: In the last years an high number of mozzarella cheese coming from Italian and German establishments caused complaints in consumers due to unusual pigmentation of dairyproducts Many microbiological analysis have been performed revealing an ubiquitous non-pathogenic bacteria, Pseudomonas fluorescens, as a causative agents liable for this phenomenon. Some specific strains of this microorganism own gene sequences coding for enzymes, able to produce dyes that can induce anomalous coloration to food. It has been verified that the occurrence of blue pigmentation in mozzarella cheese samples is however not related to chemical conditions, bacterial concentration, or critical temperature level. Both ribotyping and PFGE methodologies have underlined differences in Pseudomonas fluorescens strains isolated in food coming from different geographical areas. Nevertheless the phylogenetic assessment of bacteria pointed out no correlation between the genetic profile of the microorganism and its chromogenic behavior. the aim of this study was a deeper proteomic investigation of P. fluorescens isolates in order to evaluate how these bacteria could represent contamination source. Methods: A shotgun proteomic approach has been performed on isolated Pseudomonas fluorescens cultures coming from samples of mozzarella cheese either showing anomalous pigmentation or not. LC-MSMS experiments have been carried on by nanoHPLC runs and auto MSn acquisitions on a Bruker amaZon-ETD Ion Trap instrument. Protein identification has been executed either versus Pseudomonas dedicated DBs or on the open-reviewed databases. Results and Discussion: Obtained data highlighted several differential expressed proteins in two conditions. Among these, key proteins are, on one hand, the major cold shock protein that increases its level in the anomalous pigmentation, and, on the other, the phosphate starvation-inducible protein that decreases respect to normal condition. Conclusion: Proteomics analysis could allowed us to differentiate among chromogenic and non chromogenic strains at the molecular level, widening the knowledge on this bacteria and the molecular mechanism underlying this contamination. (P09.23)