Cultivation and maintaining survivability of bifidobacteria in fermented milk are difficult and industrially valuable tasks. We succeeded in developing a novel technique, which enable an elongated shelf life of yogurt with high viable cell counts of bifidobacteria, by co-cultivation with some strains of Lactococcus lactis subsp. lactis. Topics including screening of Lactococcus lactis strains, possible mechanisms involved in improved growth and survivability of bifidobacteria with a focus on studies targeted at Bifidobacterium longum BB536 will be introduced.

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Lactobacillus delbrueckii ssp. bulgaricus OLL1073R-1 (1073R-1) was selected from 139 Lactobacillus bulgaricus strains on the basis of exopolysaccharide (EPS) production and interferon-gamma-inducing activity. Oral administration of either EPS or yogurt fermented with this strain (1073R-1 yogurt) resulted in enhanced natural killer (NK) cell activity in animal studies. Therefore, we evaluated whether the intake of 1073R-1 yogurt can enhance human NK cell activity, and if it can inhibit the spread of respiratory tract infections, such as the common cold and influenza virus infections. The intake of 1073R-1 yogurt by healthy, elderly subjects was found to significantly reduce the risk of catching the common cold, and increased NK cell activity in subjects who had low levels of NK cell activity prior to intake. In addition, oral administration of either 1073R-1 yogurt or EPS prolonged the survival of influenza virus-infected mice. These results for 1073R-1 yogurt suggest the effect depends on the immunostimulatory EPS. Thus, we investigated ways to increase the amount of EPS in 1073R-1 yogurt. Several useful methods (increasing solids-not-fat, lowering the fermentation temperature, and addition of Na₂HPO₄, etc.) were explored, but prolonged fermentation time was a common problem for these methods. Further investigation is required to develop a yogurt which contains elevated levels of immunostimulatory EPS.

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There are few reports concerning the function of metabolites produced by gut microbiota. Polyamines are one of the most important metabolites produced by gut microbiota affecting the health and disease of the host. Polyamines have many functions, such as the maturation and maintenance of intestinal mucosal barrier, anti-inflammatory actions, antimutagenicity, and autophagy. In our recent study, longevity in mice was promoted by the administration of Bifidobacterium animalis subsp. lactis LKM512, which upregurates gut bacterial polyamine production. This paper reviews the promotion of longevity following LKM512 administration and introduces the metabolomics analysis using capillary electrophoresis with time-of-flight mass spectrometry (CE-TOF MS) for clarification of metabolite profiles in the gut lumen.

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Since 2001, DNA sequencing technology has been revolutionized. Currently, only using one sequencer, 10-100 times higher number of sequences than human genome sequences can be obtained in a day. Environmental community genomics (metagenomics) using the next generation sequencing technology have been also significantly advanced and widely and actively used in Europe and the United States for better understanding of unknown biological functions in environmental microorganisms. In such a revolutionized sequencing era, how have cultivation-based studies advanced? This review focuses on recent advances, current technological issues, promising technologies and future directions in culturing the uncultured microorganisms widely and abundantly present in the environments.

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