Requirements for sulfur in cell density-independent induction of luminescence in Vibrio fischeri under nutrient-starved conditions

Despite the universal requirement for sulfur in living organisms, it is not known whether the luminescence of Vibrio fischeri is sulfur-dependent and how sulfur affects the intensity of its luminescence. In this study, we investigated the requirement for sulfur in V. fischeri luminescence under nutrient-starved conditions. Full induction of V. fischeri luminescence required MgSO(4); in artificial seawater cultures that lacked sufficient MgSO(4), its luminescence was not fully induced. This induction of luminescence was not dependent on autoinduction because the cell density of V. fischeri did not reach the critical threshold concentration. In addition to MgSO(4), this cell density-independent luminescence was induced or maintained by nontoxic concentrations of l-cysteine, sulfate, sulfite, and thiosulfate. Moreover, the addition of N -3-oxo-hexanoyl homoserine lactone and N -octanoyl homoserine lactone, which are known autoinducers in V. fischeri, did not induce luminescence under these conditions. This result suggested that the underlying mechanism of luminescence may be different from the known autoinduction mechanism.