The critical role of urease in yogurt fermentation with various combinations of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus

Abstract

The protocooperation between Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus relies on metabolite exchanges that accelerate acidification during yogurt fermentation. Conflicting results have been obtained in terms of the effect of the Strep. thermophilus urease and the NH 3 and CO 2 that it generates on the rate of acidification in yogurt fermentation. It is difficult to perform a systematic study of the effects of urease on protocooperation because it is necessary to distinguish among the direct, indirect, and strain-specific effects resulting from the combination of the strains of both species. To evaluate the direct effects of urease on protocooperation, we generated 3 ureasedeficient mutants (∆ureC) of fast-and slow-acidifying Strep. thermophilus strains and observed the effects of NH 3 or CO 2 supplementation on acidification by the ∆ureC strains. Further, we examined 5 combinations of 3 urease-deficient ∆ureC strains with 2 CO 2 -responsive or CO 2 -unresponsive strains of L. bulgaricus. Urease deficiency induced a shortage of ammonia nitrogen and CO 2 for the fast-and slow-acidifying Strep. thermophilus and for the CO 2 -responsive L. bulgaricus, respectively. Notably, the shortage of ammonia nitrogen had more severe effects than that of CO 2 on yogurt fermentation, even if coculture with L. bulgaricus masked the effect of urease deficiency. Our work established (1) that urease deficiency inhibits the fermentative acceleration of protocooperation regardless of the Strep. thermophilus and L. bulgaricus strain combinations, and (2) that urease is an essential factor for effective yogurt acidification.

Short communication: Lactose utilization of Streptococcus thermophilus and correlations with β-galactosidase and urease

“…However, there are conflicting views regarding the role of urease in yogurt fermentation. Yamauchi et al (2019) observed that urease deficiency severely reduced acidification rates and bacterial counts in fermented milk and con-…”

“…The critical factor in the selection of S. thermophilus for application in fermented milk is its ability to rapidly metabolize lactose and produce acids. Its other essential aspects include its urease activity, proteolytic activity, and exopolysaccharide production (Iyer et al, 2010;Wu et al, 2014;Yamauchi et al, 2019).…”

“…Unlike the general presence of β-galactosidase among lactic acid bacteria, urease is an enzyme that is present only in S. thermophilus (Mora et al, 2002(Mora et al, , 2005, and is known for its ability to catalyze urea into ammonia and carbon dioxide (Yamauchi et al, 2019). However, there are conflicting views regarding the role of urease in yogurt fermentation.…”

Lipoteichoic Acid Is Involved in the Ability of the Immunobiotic Strain Lactobacillus plantarum CRL1506 to Modulate the Intestinal Antiviral Innate Immunity Triggered by TLR3 Activation

“…The mutant D-alanyl-lipoteichoic acid biosynthesis protein knockout L. plantarum CRL1506 strain (L. plantarum dltD) was obtained according to the method described by Yamauchi et al (12). Briefly, the dltD gene was obtained by PCR using primers No.…”

Comparative Genomics of Streptococcus thermophilus Support Important Traits Concerning the Evolution, Biology and Technological Properties of the Species

“…The stability of the mutated phenotype was confirmed, providing promising results regarding the potential use of ureasedeficient strains as starters in dairy fermentations (Ninova-Nikolova and Urshev, 2013). However, in a recent study employing urease deficient mutants it was suggested that urease activity is important for yogurt acidification and that its absence inhibits fermentation acceleration during protocooperation with L. bulgaricus (Yamauchi et al, 2019).…”