Seawater activation of Escherichia coli gene promoter elements: Dominance of rpoS control

The release of non-disinfected wastewater into the marine environment is a common practice in many countries; nevertheless, the molecular mechanisms involved in determining the survival of enteric bacteria in seawater are poorly understood, in spite of the obvious public health implications. In a methodological attempt to address this issue, a plasmid-based collection of 687 Escherichia coli distinct promoter::luxCDABE fusions was screened to identify promoters that are induced upon exposure to seawater. The luminescence driven by 22 out of these promoters reproducibly increased at least two-fold in an artificial seawater medium; only 9 of the corresponding genes have previously been assigned a function. The most prominent characteristic of the induced genes was that most (18 out of 22) were under rpoS control. The induction of these seawater-responsive promoters was evaluated in different media to identify the cause of the increased transcription. Salinity or osmolarity was instrumental in only four cases, and in three promoters, increased pH also seemed to play a role; however, the most significant environmental effector in inducing the majority of the seawater-induced promoters appeared to be nutrient limitation.