Effects of Magnesium Sulfate on the Luminescence of Vibrio fischeri under Nutrient-Starved Conditions

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In this study, we investigated the relationship between MgSO4 and luminescence in Vibrio fischeri under nutrient-starved conditions. When V. fischeri was cultured in an artificial seawater medium, the luminescence intensity was low relative to that observed under normal growth conditions. It decreased during the initial 14 h, and then increased slightly at 24 h. This regulation of luminescence was not dependent on the quorum-sensing mechanism, because the cell densities had not reached a critical threshold concentration. Under MgSO4-starved conditions, luminescence was not fully induced at 14 h, and decreased at 24 h. In contrast, induction of luminescence occurred under MgSO4-supplemented conditions, but MgSO4 alone was insufficient to induce luminescence, and required NaHCO3 or KCl. These results suggest that the luminescence of V. fischeri is controlled by an exogenous sulfur source under nutrient-starved conditions. In addition, they indicate that the induction of sulfur-dependent luminescence is regulated by the NaHCO3 or KCl concentration.