Molecular genetic and biochemical approaches are applied. Two genetically and biochemically distinct nitrate reductases are present to fulfill the dual roles, in contrast, a single nitrite reductase functions in both assimilation and respiration. The functional differences of the enzymes correspond to the differences in the gene regulation. We have studied how these nitrate and nitrite reductase genes are regulated in response to nitrogen and oxygen limitation by promoter analysis of these genes and identification of trans-acting factors. Two-Component Signal Transduction System Bacteria often encounter sudden environmental changes.
Cells cope with such changes by an elaborate network of adaptive responses.
The two-component signal transduction system senses and then processes information derived from environmental changes so that the cell can choose the appropriate adaptive response. This simple signal transduction system is widespread in bacteria and also found in plants and lower eukaryotes. ResE is a histidine kinase and ResD is a response regulator of this large protein family. We have shown that ResD and ResE are indispensable for anaerobic respiration in B. subtilis . B. subtilis hmp was identified among genes, expression of which are induced by oxygen limitation.