Bacterial operon inducible

It transpires that the heat shock genes of one single bacterial species are regulated by different mechanisms. Genes and operons controlled by one particular regulator are called regulons and, if there are at least two regulons in one species induced by the same stress factor, they form a stimulon. 

Revelles O, M Espinosa-Urgel, S Molin, JL Ramos (2004) The davDT operon of Pseudomonas putida, involved in lysine catabolism, is induced in response to the pathway intermediate 5-aminovaleric acid. J Bacterial 186 3439-3446. 

Transcription ofT7 RNA polymerase is induced by addition of isopropyl-p-D-thiogalactoside. The polymerase then directs the transcription of the lipase operon. The lipase is correctly folded and secreted into the bacterial culture supernatant which can subsequently be used to assay lipase activities. 

In the presence of nitrate, formate dehydrogenase-N (FDH-N) and nitrate reductase are induced (8). As a result, the formate is consumed preferentially by FDH-N due to its inherent high affinity for formate versus FDH-H. The Km value for formate of FDH-N is 0.12 mM, while that of FDH-H is 26 mM. The FHL system is induced by the presence of formate, however, formate consumption by an FDH-N - nitrate reductase system depresses the expression level of the FHL system. Consequently, both expression of FHL and hydrogen production are repressed by the presence of nitrate in the medium. The removal of nitrate from waste water is not a practical process therefore a bacterial strain capable of hydrogen production even in the presence of nitrate is favorable. The subunits of nitrate reductase are encoded in the fdn operon. The a-subunit of nitrate reductase is encoded in the... 

Much of the experimental evidence on which the operon theory is based was obtained by studying the induction and repression of bacterial enzymes. Induction is indicated by an increase in enzyme activity, and repression by a decrease in that activity. The inducer is usually a substrate of the enzyme the repressor is usually a product of the enzyme reaction. The changes in enzyme activities result from alterations in the rate of protein synthesis. 

The conclusion to be drawn from the results of this experimental work is that if a series of reactions catalyzed by several enzymes in succession is necessary for a particular biochemical process, the genes determining them show a tendency to be arranged in the bacterial chromosome in a single cluster, the operon. The operon can be in an active or repressed state depending on the presence or absence of substrate (inducer). 

Martin, M., Magni, C., Lopez, R, and de Mendoza, D. (2000) Transcriptional control of the citrate-inducible citMCDEFGRP operon, encoding genes involved in citrate fermentation in Leuconostoc paramesenteroides. J Bacterial 182,3904-3912. 

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