Biofilm Formation on Stainless Steel by Streptococcus thermophilus UC8547 in Milk Environments Is Mediated by the Proteinase PrtS.
InStreptococcus thermophilus, gene transfer events and loss of ancestral traits over the years contribute to its high level of adaptation to milk environments. Biofilm formation capacity, a phenotype that is lost in the majority of strains, plays a role in persistence in dairy environments, such as milk pasteurization and cheese manufacturing plants. To investigate this property, we have studiedS. thermophilusUC8547, a fast-acidifying dairy starter culture selected for its high capacity to form biofilm on stainless steel under environmental conditions resembling the dairy environment. Using a dynamic flow cell apparatus, it was shown thatS. thermophilusUC8547 biofilm formation on stainless steel depends on the presence of milk proteins. From this strain, which harbors theprtSgene for the cell wall protease and shows an aggregative phenotype, spontaneous mutants with impaired biofilm capacity can be isolated at high frequency. These mutants lack the PrtS expendable island, as confirmed by comparison of the genome sequence of UC8547Δ3 with that of the parent strain. TheprtSisland excision occurs between two 26-bp direct repeats located in the two copies of the ISSth1flanking this genomic island. The central role of PrtS was confirmed by analyzing the derivative strain UC8547Δ16, whoseprtSgene was interrupted by an insertional mutation, thereby making it incapable of biofilm formation. PrtS, acting as a binding substance between the milk proteins adhered to stainless steel andS. thermophiluscell envelopes, mediates biofilm formation in dairy environments. This feature providesS. thermophiluswith an ecological benefit for its survival and persistence in this environment.IMPORTANCEThe increased persistence ofS. thermophilusbiofilm has consequences in the dairy environment: if, on the one hand, the release of this microorganism from biofilm can promote the fermentation of artisanal cheeses, under industrial conditions it may lead to undesirable contamination of dairy products. The study of the molecular mechanism drivingS. thermophilusbiofilm formation provides increased knowledge on how an ancestral trait affects relevant phenotypes, such as persistence in the environment and efficiency of growth in milk. This study provides insight into the genetic factors affecting biofilm formation at dairy plants.
Istituto di Microbiologia, Centro Ricerche Biotecnologiche, Università Cattolica del Sacro Cuore, Piacenza and Cremona, Italy.
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http://orcid.org/0000-0001-9020-3853
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Bassi
Istituto di Microbiologia, Centro Ricerche Biotecnologiche, Università Cattolica del Sacro Cuore, Piacenza and Cremona, Italy.
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Cappa
Istituto di Microbiologia, Centro Ricerche Biotecnologiche, Università Cattolica del Sacro Cuore, Piacenza and Cremona, Italy.
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Gazzola
Consiglio per la Ricerca e la Sperimentazione in Agricoltura e l'Analisi dell'Economia Agraria, Centro di Ricerca per la Genomica Vegetale (CREA-GPG), Fiorenzuola d'Arda, Italy.
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Orrù
Istituto di Microbiologia, Centro Ricerche Biotecnologiche, Università Cattolica del Sacro Cuore, Piacenza and Cremona, Italy pier.cocconcelli@unicatt.it.
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Cocconcelli
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D018441:Biofilms / Q000254:growth & development*; D002473:Cell Wall / Q000378:metabolism; D016680:Genome, Bacterial; D044404:Genomic Islands; D008892:Milk / Q000737:chemistry / Q000382:microbiology*; D008894:Milk Proteins / Q000378:metabolism; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism*; D013193:Stainless Steel; D048249:Streptococcus thermophilus / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000502:physiology
D001426:Bacterial Proteins; D008894:Milk Proteins; D013193:Stainless Steel; C417204:PrtS protein, Streptococcus thermophilus; D012697:Serine Endopeptidases
PrtS; Streptococcus thermophilus; biofilm; genome; milk; stainless steel