title: Streptococcus thermophilus urease activity boosts Lactobacillus delbrueckii subsp. bulgaricus homolactic fermentation.
abstract: The proto-cooperation between Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus in the yogurt consortium enhances the growth rate and size of each population. In contrast, the independent growth of the two species in milk leads to a slower growth rate and a smaller population size. In this study, we report the first evidence that the urease activity of S. thermophilus increases the intracellular pH of L. delbrueckii in the absence of carbon source. However, in milk, in the presence of lactose the alkalizing effect of urea-derived ammonia was not detectable. Nevertheless, based on glucose consumption and lactic acid production at different pHin, L. delbrueckii showed an optimum of glycolysis and homolactic fermentation at alkaline pH values. In milk, we observed that ammonia provided by urea hydrolysis boosted lactic acid production in S. thermophilus and in L. delbrueckii when the species were grown alone or in combination. Therefore, we propose that urease activity acts as an altruistic cooperative trait, which is costly for urease-positive individuals but provides a local benefit because other individuals can take advantage of urease-dependent ammonia release.
authors.affiliation: Department of Food Environmental and Nutritional Sciences (DeFENS), University of Milan, Italy. Electronic address: stefania.arioli@unimi.it.
authors.forename: Stefania
authors.initials: S
authors.lastname: Arioli
authors.affiliation: Department of Food Environmental and Nutritional Sciences (DeFENS), University of Milan, Italy.
authors.forename: Giulia
authors.initials: G
authors.lastname: Della Scala
authors.affiliation: Sacco srl, Cadorago (CO), Italy.
authors.forename: Maria Chiara
authors.initials: MC
authors.lastname: Remagni
authors.affiliation: Department of Food Environmental and Nutritional Sciences (DeFENS), University of Milan, Italy.
authors.forename: Milda
authors.initials: M
authors.lastname: Stuknyte
authors.affiliation: Department of Food Environmental and Nutritional Sciences (DeFENS), University of Milan, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Colombo
authors.affiliation: Department of Food Environmental and Nutritional Sciences (DeFENS), University of Milan, Italy.
authors.forename: Simone
authors.initials: S
authors.lastname: Guglielmetti
authors.affiliation: Department of Food Environmental and Nutritional Sciences (DeFENS), University of Milan, Italy.
authors.forename: Ivano
authors.initials: I
authors.lastname: De Noni
authors.affiliation: Department of Food Environmental and Nutritional Sciences (DeFENS), University of Milan, Italy.
authors.forename: Enzio
authors.initials: E
authors.lastname: Ragg
authors.affiliation: Department of Food Environmental and Nutritional Sciences (DeFENS), University of Milan, Italy.
authors.forename: Diego
authors.initials: D
authors.lastname: Mora
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D005285:Fermentation; D019344:Lactic Acid / Q000096:biosynthesis*; D048668:Lactobacillus delbrueckii / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D008892:Milk / Q000382:microbiology; D048249:Streptococcus thermophilus / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D014510:Urease / Q000235:genetics / Q000378:metabolism*; D015014:Yogurt / Q000382:microbiology
chemical_list: D001426:Bacterial Proteins; D019344:Lactic Acid; D014510:Urease