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Yogurt is made by fermenting milk with 2 lactic acid bacteria, Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus. To comprehensively understand the protocooperation mechanism between S. thermophilus and L. bulgaricus in yogurt fermentation, we examined 24 combinations of cocultures comprising 7 fast- or slow-acidifying S. thermophilus strains with 6 fast- or slow-acidifying L. bulgaricus strains. Furthermore, 3 NADH oxidase (Nox)-deficient mutants (Δ nox) and one pyruvate formate-lyase deficient mutant (Δ pflB) of S. thermophilus were used to evaluate the factor that determines the acidification rate of S. thermophilus. The results revealed that the acidification rate of S. thermophilus monoculture determined the yogurt fermentation rates, despite the coexistence of L. bulgaricus, whose acidification rate was either fast or slow. Significant correlation was found between the acidification rate of S. thermophilus monoculture and the amount of formate production. Result using Δ pflB showed that the formate was indispensable for the acidification of S. thermophilus. Moreover, results of the Δ nox experiments revealed that formate production required Nox activity, which not only regulated dissolved oxygen, but also the redox potential. The Nox provided the large decrease in redox potential required by pyruvate formate-lyase to produce formate. A highly significant correlation was found between formate accumulation and Nox activity in S. thermophilus. In conclusion, the formate production ability provided by the action of Nox activity determines the acidification rate of S. thermophilus, and consequently, regulates yogurt coculture fermentation. [ABSTRACT FROM AUTHOR]

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 NH3 and CO2 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 urease-deficient mutants (ΔureC) of fast- and slow-acidifying Strep. thermophilus strains and observed the effects of NH3 or CO2 supplementation on acidification by the ΔureC strains. Further, we examined 5 combinations of 3 urease-deficient ΔureC strains with 2 CO2-responsive or CO2-unresponsive strains of L. bulgaricus. Urease deficiency induced a shortage of ammonia nitrogen and CO2 for the fast- and slow-acidifying Strep. thermophilus and for the CO2-responsive L. bulgaricus, respectively. Notably, the shortage of ammonia nitrogen had more severe effects than that of CO2 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. [ABSTRACT FROM AUTHOR]

Abstract: Epitaxial growth of LaB6 (100) thin films was examined on MgO (100) and sapphire (α-Al2O3) (0001) substrates with insertion of a 2–3nm-thick epitaxial SrB6 buffer layer by pulsed laser deposition in ultra-high vacuum. Reflection high-energy electron diffraction, X-ray diffraction, and the Raman scattering spectroscopy measurements proved that the heteroepitaxial structure of the LaB6 (100)/SrB6 (100)/MgO (100) substrate has a single-domain, while and that of the LaB6 (100)/SrB6 (100)/sapphire (0001) substrate have three domains. LaB6 thin films grown without the buffer layer were not epitaxial; instead, they developed as polycrystalline films with a random in-plane configuration. The buffer layer greatly affected the initial growth of the LaB6 thin films. Epitaxial LaB6 thin films exhibited metallic behavior with almost constant resistivities in the temperature range 12–300K. At room temperature, the resistivities of single-domain LaB6 (100) epitaxial thin films on MgO substrates were about 5 times smaller than those of the three-domain LaB6 (100) epitaxial thin films on the sapphire substrates. [Copyright &y& Elsevier]

Abstract: Since the prediction of a CDW state in alkali metals by Overhauser in 1962, many groups tried to observe this state. However no clear evidence has been reported. We attempted to observe the phase transition in potassium and observed anomalous behavior at about 20K in magnetic susceptibility, specific heat and lattice constant. To confirm the phase transition at about 20K in potassium, a muon-spin-relaxation experiment was performed between 10 and 50K. Temperature dependence of the dynamical rate increases below about 20K. [Copyright &y& Elsevier]