Interactions Between pH, Potassium, Calcium, Bromide, and Phenol and Their Effects on the Bioluminescence of Vibrio fischeri

Little attention has been paid to how the light produced by the bacterium Vibrio fischeri in the Microtox assay is dependent on the concentration of essential ions such as sodium and potassium, and whether the concentrations of these ions affect the sensitivity of the test system to toxic chemicals. Five selected factors, pH, potassium (K+), calcium (Ca2+), bromide (Br-), and phenol (Phe), were simultaneously varied over a set of systematically planned experiments according to a D-optimal design that supported the estimation of a model with linear, quadratic, and two-factor interatcions of the studied factors. The bacterial light production represented by the gamma values in the Microtox assay for the 24 selected combinations of factors was measured at 5 and 15 min. The gamma values varied from negative to positive values greater than 1, indicating stimulation and inhibition of bacterial light production, respectively. The relationship between the gamma values and the factor settings was investigated with multiple linear regression. After 5 min of exposure, the light production was significantly affected by linear and quadratic terms for K+, pH, and Phe and an interaction between pH and Phe. The situation was more complex after 15 min of exposure, since in addition significant interactions were found for K x Phe and Ca x pH. The tolerance of V. fischeri to Phe was enhanced by increasing the K and Ca concentrations. Data indicate that the ion composition and pH of the sample, as well as the diluents, need to be considered when the toxicity of salts, water samples, and extracts of sediments and soils are tested using commercially certified toxicity test kits.