Effect of solution type and volume toxicity of lipopolysaccharide on <i>Vibrio fischeri</i> bioluminescence inhibition

Toxicity tests with marine luminescent bacteria, such as <i>Vibrio fischeri</i>, typically require a 2-3% NaCl adjustment to simulate marine environments. However, this addition may inadvertently promote bacterial growth, leading to an overestimation of toxicity. This study investigates the toxicity of lipopolysaccharides (LPS), components of the outer membrane of Gram-negative bacteria that pose significant health risks. We focused on the interaction between LPS and <i>V. fischeri</i>, assessing its bioluminescent response. Measuring LPS toxicity through bioluminescence inhibition necessitates careful consideration of how NaCl impacts bacterial growth and LPS toxicity. The effects of LPS on bioluminescence were studied in two solutions: 3% NaCl and photobacterium medium. Experiments utilized three injection volumes (25, 50, and 75 μL) and a range of LPS concentrations (1 × 10^-1 to 1 × 10^-10 mg/mL). Results demonstrated that the type of solution, LPS concentration, and injection volume significantly affected bioluminescence. The strongest inhibition was observed at a concentration of 1 × 10^-3 mg/mL in a photobacterium medium (74%) and 3% NaCl at a concentration of 1 × 10^-1 mg/mL (65%). The effective concentrations (EC₅₀) revealed the highest toxicity in the photobacterium medium (EC₅₀ = 3.08 × 10^-5 mg/mL at 50 μL) compared to 3% NaCl (EC₅₀ = 0.0003 mg/mL at 25 μL).