Quorum sensing, a cell-density-dependent regulatory system, which controls aggressive phenotype to other organism such as bacteriocin biosynthesis or virulence expression, is an efficient strategy for a certain species of bacteria to survive in nature of complex ecosystem. In this review, general aspect of quorum sensing is introduced and then peptide pheromone-mediated quorum sensing of Gram-positive bacteria focussing on the regulation of bacteriocin biosynthesis in lactic acid bacteria and control of virulence expression in staphylococci is reviewed.

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Aspartate in soy sauce morormi was sometimes decarboxylated into alanine by the strains of soy sauce lactic acid bacteria, Tetragenococcus halophilus. Because this amino acid conversion makes taste of soy sauce milder, aspartate decarboxylating strain (Asd⁺ strain) of T. halophilus is important strains in soy sauce manufacturing.
T. halophilus D10 is an Asd⁺ strain. Curing treatment of this strain generated derivative strains that could not cause aspartate decarboxylation (Asd^- strains). This trait was coded on a 22kb plasmid named pD1. On this plasmid aspartate transporter and aspartate decarboxylase genes formed operon.
Continuous usage of a single strain of lactic acid bacteria in large scale industrial manufacturing cause bacteriophage infection, so phage insensitive strain of D10 strain was prepared to use this Asd+ strain in the factory without phage infection.
Physiological reason of aspartate decarboxylation of T. halophilus is not clear yet. However, another lactic acid bacteria which cause aspartate decarboxylation, Lactobacillus sp. M3, derive energy as proton-motive force coupled with the decarboxylation. It is assumed that energy production by similar mechanism occurred in Asd+ strain of T. halophilus.

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The Recombinant DNA (rDNA) techniques are expected to bring about a great progress in the improvement of breeding technology and the development of new plant varieties showing high quality and high yield, such as those with excellent pest and disease resistances, those with environmental stress tolerance, etc. In the USA, a late ripening tomato variety developed through the rDNA technology was commercialized as the world's first recombinant food in 1994. Seven transgenic crop plants, such as herbicide tolerant soybean and canola, insect resistant corn and potato, were complied all safety assessments with the guidelines required and they are marketable in Japan. The general public, however, are not familiar with rDNA technologies, and some seem to feel uncomfortable with biotechnology. It is caused by the difficulty of the technology and lacking of sufficient information. In order to promote agricultural biotechnology, it is important to give precise information about rDNA technologies to the general public so that public awareness to the techniques should be improved. Because, the rDNA techniques are most important technologies to improve world's food supply and global environment in the next century.

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Twenty-two strains of Lactobacillus acidophilus were tested for their bile acid tolerance. The recovery rates of three of these strains were measured in feces of volunteers administered individual doses of these strains. A L92 strain with the highest bile acid tolerance (5.77%)showed the highest recovery rate in feces (93%). On the other hand, a CP1553 strain with the lowest bile acid tolerance (0.75%) showed the lowest recovery rate in feces (0.0056%). Positive correlation was observed between the bile acid tolerance and the recovery of the tested Lactobacillus acidophilus strains in feces. Bile acid tolerance seemed to be very important characteristic for the survival and reisolation of strains from feces for Lactobacillus acidophilus. Moreover, the selected L92 strain was able to prevent attachment of harmful bacteria to Caco-2cells. These results indicate the potential usefulness of Lactobacillus acidophilus strain L92 as a probiotic.

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