The yjbEFGH operon of Escherichia coli was previously shown to be involved in exopolysaccharide production and induced during biofilm formation by osmotic stress; in this communication we investigate some of the factors taking part in its regulation. We show that induction of yjbF'::luxCDABE transcriptional fusion in response to osmotic shock is limited to the early growth phase of batch-grown cells, and is dictated by cell density in an oxygen-related manner: induction was maximal at low cell density and at high oxygen concentrations. The dependency on cell density and oxygen availability was verified in both batch and continuous culture, using either bioluminescence (luxCDABE) or beta-galactosidase (lacZ) genes as the reporter system. It is further shown that yjb is also induced by low specific growth rates, even in the absence of osmotic stress. Finally, it is demonstrated that induction of the yjbEFGH operon, though clearly a stress response, is not a part of the general stress regulon under the positive control of RpoS, as it is negatively affected by this sigma factor.