Yogurt Production.

Yogurt is a popular fermented dairy product produced by lactic acid bacteria, including Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. During yogurt production, these bacteria produce lactic acid, decreasing pH and causing milk protein to coagulate. Their metabolites, such as carbonyl compounds, nonvolatile or volatile acids, and exopolysaccharides, strongly affect the quality of yogurt. In this chapter, the general methods for yogurt production are summarized.

Interactions between salivary Bifidobacterium adolescentis and other oral bacteria: in vitro coaggregation and coadhesion assays.

Coaggregation assays were performed to investigate interactions between oral Bifidobacterium adolescentis and other oral bacterial species. Bifidobacterium adolescentis OLB6410 isolated from the saliva of healthy humans did not coaggregate with Actinomyces naeslundii JCM8350, Streptococcus mitis OLS3293, Streptococcus sanguinis JCM5708, Veillonella parvula ATCC17745 or Porphyromonas gingivalis OB7124, but it did coaggregate with Fusobacterium nucleatum JCM8532. Subsequent examination of biofilm formation on saliva-coated hydroxyapatite discs using FISH revealed that B. adolescentis OLB6410 could not directly adhere to the coated discs. It did, however, adhere to biofilms of A. naeslundii, V. parvula, and F. nucleatum, although it did not coaggregate with A. naeslundii nor with V. parvula. These results suggest that the adhesion of B. adolescentis to tooth surfaces is mediated by other oral bacteria. Heat- or proteinase K-treated F. nucleatum could not coaggregate with B. adolescentis. Similarly, the coaggregation and coadhesion of proteinase K-treated B. adolescentis were strongly inhibited. It is therefore probable that proteinaceous factors on the cellular surface of B. adolescentis and F. nucleatum are involved in their interaction. The data presented in this study add to our understanding of bifidobacterial colonization in the human oral cavity.

Identification of five phospho-beta-glycosidases from Lactobacillus gasseri ATCC33323T cultured in lactose medium.

Lactobacillus gasseri ATCC33323(T) has seven putative phospho-beta-glycosidase genes. Using column chromatography, we found that this strain cultured in lactose medium expresses five phospho-beta-glycosidases (LacG1, LacG2, Pbg1, Pbg2, and Pbg3), where these gene expressions can be suppressed by glucose. To our knowledge, this is the first report indicating that five glycosidases are induced from a single bacterial strain using a single carbon source, lactose.

Purification and characterization of two phospho-ß-galactosidases, LacG1 and LacG2, from Lactobacillus gasseri ATCC33323(T).

Lactobacillus gasseri ATCC33323(T) expresses four enzymes showing phospho-ß-galactosidase activity (LacG1, LacG2, Pbg1 and Pbg2). We previously reported the purification and characterization of two phospho-ß-galactosidases (Pbg1 and Pbg2) from Lactobacillus gasseri JCM1031 cultured in lactose medium. Here we aimed to characterize LacG1 and LacG2, and classify the four enzymes into 'phospho-ß-galactosidase' or 'phospho-ß-glucosidase.' LacG1 and recombinant LacG2 (rLacG2), from Lb. gasseri ATCC33323(T), were purified to homogeneity using column chromatography. Kinetic experiments were performed using sugar substrates, o-nitrophenyl-ß-D-galactopyranoside 6-phosphate (ONPGal-6P) and o-nitrophenyl-ß-D-glucopyranoside 6-phosphate (ONPGlc-6P), synthesized in our laboratory. LacG1 and rLacG2 exhibited high k(cat)/K(m) values for ONPGal-6P as compared with Pbg1 and Pbg2. The V(max) values for ONPGal-6P were higher than phospho-ß-galactosidases previously purified and characterized from several lactic acid bacteria. A phylogenetic tree analysis showed that LacG1 and LacG2 belong to the phospho-ß-galactosidase cluster and Pbg1 and Pbg2 belong to the phospho-ß-glucosidase cluster. Our data suggest two phospho-ß-galactosidase, LacG1 and LacG2, are the primary enzymes for lactose utilization in Lb. gasseri ATCC33323(T). We propose a reclassification of Pbg1 and Pbg2 as phospho-ß-glucosidase.