title: Strain Diversity of Pseudomonas fluorescens Group with Potential Blue Pigment Phenotype Isolated from Dairy Products.
abstract: The blue discoloration in Mozzarella cheese comes from bacterial spoilage due to contamination with Pseudomonas. Fourteen Pseudomonas fluorescens strains from international collections and 55 new isolates of dominant bacterial populations from spoiled fresh cheese samples were examined to assess genotypic and phenotypic strain diversity. Isolates were identified by 16S rRNA gene sequencing and tested for the production of the blue pigment at various temperatures on Mascarpone agar and in Mozzarella preserving fluid (the salty water in which the cheese is conserved, which becomes enriched by cheese minerals and peptides during storage). Pulsed-field gel electrophoresis analysis after treatment with the endonuclease SpeI separated the isolates into 42 genotypes at a similarity level of 80%. Based on the pulsotype clustering, 12 representative strains producing the blue discoloration were chosen for the multilocus sequence typing targeting the gyrB, glnS, ileS, nuoD, recA, rpoB, and rpoD genes. Four new sequence typing profiles were discovered, and the concatenated sequences of the investigated loci grouped the tested strains into the so-called ''blue branch'' of the P. fluorescens phylogenetic tree, confirming the linkage between pigment production and a specific genomic cluster. Growth temperature affected pigment production; the blue discoloration appeared at 4 and 14°C but not at 30°C. Similarly, the carbon source influenced the phenomenon; the blue phenotype was generated in the presence of glucose but not in the presence of galactose, sodium succinate, sodium citrate, or sodium lactate.
authors: Department of Food, Environmental and Nutritional Sciences, Università degli Studi di Milano, Via G. Celoria, 2-20133 Milano, Italy.
authors: Margherita
authors: M
authors: Chierici
authors: Department of Food, Environmental and Nutritional Sciences, Università degli Studi di Milano, Via G. Celoria, 2-20133 Milano, Italy.
authors: Claudia
authors: C
authors: Picozzi
authors: Department of Food, Environmental and Nutritional Sciences, Università degli Studi di Milano, Via G. Celoria, 2-20133 Milano, Italy.
authors: Marisa Grazia
authors: MG
authors: La Spina
authors: Department of Quality, Innovation, Safety, and Environment, Granarolo S.p.A., Via Cadriano, 27/2-40127 Bologna, Italy.
authors: Carla
authors: C
authors: Orsi
authors: Department of Food, Environmental and Nutritional Sciences, Università degli Studi di Milano, Via G. Celoria, 2-20133 Milano, Italy.
authors: Ileana
authors: I
authors: Vigentini
authors: Department of Quality, Innovation, Safety, and Environment, Granarolo S.p.A., Via Cadriano, 27/2-40127 Bologna, Italy.
authors: Vittorio
authors: V
authors: Zambrini
authors: Department of Food, Environmental and Nutritional Sciences, Università degli Studi di Milano, Via G. Celoria, 2-20133 Milano, Italy. roberto.foschino@unimi.it.
authors: Roberto
authors: R
authors: Foschino
mesh_terms: D004269:DNA, Bacterial / Q000235:genetics; D003611:Dairy Products / Q000382:microbiology; D008969:Molecular Sequence Data; D010641:Phenotype; D010802:Phylogeny; D011549:Pseudomonas / Q000302:isolation & purification*; D011551:Pseudomonas fluorescens / Q000302:isolation & purification*; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA
chemical_list: D004269:DNA, Bacterial; D012336:RNA, Ribosomal, 16S