Objective: To obtain a strain which has stronger antagonistic effect against Streptococcus mutans(S. mutans), and then to study the antagonistic effect of the fermentation filtrate of the strains. Method:Surface soil samples were harvested and used in an in vitro bacteria culture system for screening of antagonistic strains against Streptococcus mutans. Ferment filtrate of the strains was respectively prepared and the antagonism of the filtrate against S. mutans was examined.Result:A strain with strong restrain effect on Streptococcus mutans was found and was identified to be Bacillus licheniformis. The strain was named strain 1#. At pH 7.0, 150 r/min and constant temperature of 30 ℃ cultivated for 24 hours,the antagonistic energy of ferment filtrate was 1 500 IU/ml,the ferment filtrate showed strong heat stability, at 37 ℃ for 1 hour, the activity decreased by 35%; at 60 ℃ for 30 min, by 47%, for 1 h, by 50%, at 100 ℃,the activity maintained 39%.The optimum pH for the activity of the ferment filtrate was 7.0, at pH 3.0, the activity kept 70% and at pH 11.0, 65%.Conclusion:The fermentation filtrate of strain 1# of Bacillus licheniformis is antagonistic against S. mutans.

On the basis of the analysis of metabolic mechanism and related enzymes of microorganisms that produce dicarboxylic acid, the newest evolution of modern biotechnology, for example, genetic engineering and metabolic regulation etc , which used in the improving of stains that applied in producing of dicarboxylic acid was generally summarized At the same time, how to combine the conventional microorganism fermentation technologies with modern biotechnology was simply discussed