Listeria monocytogenes is a serious food borne pathogenic bacterium that can cause listeriosis with high mortality rate. L. monocytogenes is commonly found in the environment particularly in association with decaying plant material.  From the environmental niche the bacterium is believed to be transmitted to food processing plants from where it can establish and survive for extended periods of time contaminating processed food products. Recently we have identified the response regulator ResD of L. monocytogenes and showed that it is important for growth in laboratory media and for sugar uptake (Larsen et al., 2006).

The aim of this study was to investigate in more detail the role of the response regulator ResD in metabolisme of Listeria monocytogenes EGD. The role of ResD was first  investigated by microarray analysis. This analysis resulted in identification of genes repressed under aerobic conditions in a resD mutant strain compared to the wild type. The majority of these were involved in motility and chemotaxis and in carbohydrate uptake such as mannose and cellobiose specific PTS uptake systems.

The role of ResD for metabolism in L. monocytogenes was also studied by northern blot analysis. This study showed that expression of ldh encoding lactate dehydrogenase was significantly reduced in the absence of resD both aerobic conditions (Fig 1) demonstrating that ResD regulated expression of ldh in L. monocytogenes.  Catabolism of glucose in L. monocytogenes proceeds by the Embden-Meyerhof pathway both aerobically and anaerobically.  Anaerobically the end product is mainly lactic acid, aerobically pyrovate, acetoin, lactic acid and other end products are formed (Jones and Seeliger, Ro...). We found that the production of acetoin during aerobic growth in broth was decreased in the resD mutant strain compared to the wild type, indicating that ResD is necessary for full induction of the alsS and alsD genes encoding acetolactate synthase and acetolactate decarboxylase responsible for the conversion of pyruvate to acetoin. Finally, binding putative binding sites for ResD were found in the upstream regulatory region of several genes of L. monocytogenes and the binding of the ResD protein to some of these regulatory regions upstream putative target genes is analysed by electrophoretic mobility shift assays (EMSAs).

In conclusion, the response regulator ResD act is important for metabolisme and act as a pleotrophic regulator in L. monocytogenes EGD.