Streptococcus mutans UA101, which was previously demonstrated to be highly cariogenic in gnotobiotic rats, exhibited much lower water-insoluble glucan (IG) synthetic activity compared with that of S. mutans GS5 and was unable to express sucrose-dependent colonization of smooth surfaces in vitro. On the basis of Southern and Western blot (immunoblot) analyses, it was demonstrated that, unlike most S. mutans strains, strain UA101 contained a single copy of a gene coding for IG synthesis. The gene was isolated from a clone bank constructed with the plasmid pTH10 clone bank in Escherichia coli and had apparently evolved after homologous recombination of the gtfB and gtJC genes present on the chromosome of a recent ancestor of strain UA101. The enzyme expressed from the gene, gtfBC, was purified to near homogeneity by utilizing a single-step preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis system and was characterized. A derivative of strain UA101, UA1O1LBS, containing a chromosomal insertion of the GS5 gtJC gene was constructed after transformation. UA1O1LBS exhibited high IG synthetic activity and colonized smooth surfaces in vitro. By utilizing a conventional rat model system involving animals fed a high-sucrose diet, strain UA101 exhibited low levels of smooth surface caries activity relative to Streptococcus sobrinus 6715. By contrast, UAIOILBS was as cariogenic as strain 6715. However, sulcal caries occurred equally well with all of the strains tested. These results are evaluated relative to the role of gtf gene products in cariogenicity. * Corresponding author. results are discussed in relation to the role of the S. mutans GTFs in cariogenesis.
The activity of explosively developing extratropical cyclones in the vicinity of Japan in intimate association with the occurrence of heavy snowfall on the Japan Sea side of central Japan is examined using Japanese long-term reanalysis projected data (JRA-25), with additional data from the Japan Meteorological Agency climate data assimilation system (JCDAS). On a monthly basis, the explosive extratropical cyclone tracks tend to concentrate around the Kuroshio Current off the Pacific coast of Japan and the Japan Sea at the heavy snowfall phase, whereas the tracks disperse over the broader areas in the light snowfall phase. The heavy and light snowfall phases correspond well to the strong and weak phases of the East Asian winter monsoon circulation respectively, and the monsoon variability influences the local monthly snowfall on the Japan Sea side of central Japan through change in the explosive cyclone activity. On a daily basis, stationary Rossby wave packets propagating eastward along the northern Eurasian and South Asian waveguides, i.e., subpolar and subtropical teleconnection types, contribute to the occurrence of extraordinarily heavy snowfall events through the development of explosive cyclones. The subpolar teleconnection type facilitates not only the intensification and southward migration of a cold continental high in East Asia, but also the rapid growth of an explosive cyclone around Japan by inducing the equatorward advection of higher potential vorticity from high latitudes. Both developments lead to the reinforcement of an east-west gradient in sea level pressure (SLP) across Japan, thereby providing a favorable condition for the heavy snowfall events. For the subtropical teleconnection type, the explosive cyclone system is primarily responsible for the occurrence of extremely heavy snowfall events through enhanced zonal SLP gradient. It is also found that the explosive cyclone activity differs in terms of geographical location and track between the subpolar and subtropical teleconnection types.
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