Differential expression of Vibrio vulnificus elastase gene in a growth phase-dependent manner by two different types of promoters

Elastase activity of Vibrio vulnificus was highly dependent on growth phase, reached a maximum during the stationary phase, and was regulated at the level of transcription. The stationary phase production of elastase in crp or rpoS mutants, which were constructed by allelic exchanges, decreased about 3- and 10-fold, respectively. However, the promoter activity of vvpE encoding elastase was unaffected by those mutations in the log phase when analyzed using a vvpE-lux fusion, A primer extension analysis revealed that the transcription of vvpE begins at two different sites, consisting of putative promoter L (PL) and promoter S (PS), The PL activity was constitutive through the log and stationary phases, lower than the PS activity, and unaffected by the crp or rpoS mutations. The transcription of PS, induced only in the stationary phase, was dependent on RpoS. The mutation in crp reduced the activity of PS; however, the additional inactivation of crp did not influence the PS activity in the rpoS mutant, indicating that CRP exerted its effects through PS requiring RpoS, These results demonstrate that vvpE expression is differentially directed by PL and PS depending on the growth phase and elevated by RpoS and CRP in the stationary phase.