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Abstract
Previous studies have suggested that the specific type and amount of carbohydrate available for growth affects the expression of virulence genes in Listeria monocytogenes. Which carbohydrates influence virulence gene expression and how carbohydrates mediate expression, however, is not clear. The goal of this project, therefore, was to determine how carbohydrates affect virulence gene expression in L. monocytogenes 10403S. Growth studies were initially conducted in a defined medium containing combinations of glucose and various sugars. Metabolism of arbutin, arabitol, cellobiose, mannose, maltose, trehalose and salicin were repressed in the presence of glucose, and only when glucose had been consumed were these sugars fermented, indicating that catabolite repression by glucose had occurred. To determine if virulence gene expression was also influenced by catabolite repression conditions, primer extension experiments were performed using primers for hly, which encodes for a hemolysin, and prfA, which encodes the regulator protein PrfA. In the presence of cellobiose and arbutin, transcription of hemolysin was markedly reduced, compared to transcription levels in all of the other sugars tested. When cells were grown in the presence of both glucose and cellobiose, there was no change in hly expression compared to cells grown on glucose only. However, none of the sugars tested affected transcription of prfA in L. monocytogenes . On the other hand, prfA could be targeted by carbohydrates at a level other than transcription such as activity. Activity of hemolysin when grown with the above mentioned sugars was also examined along with global gene expression using an expression array. These results demonstrate that catabolite repression occurs in L. monocytogenes and suggests that, at least in strain 10403S, cellobiose and arbutin repress expression of hemolysin.
