ECOTOXICOLOGY A RESEARCH ABOUT THE TOXICITY OF THE VIPAVA RIVER WITH BIOLUMINESCENT BACTERIA VIBRIO FISCHERI Authors: Nina, Tina, Francesco, Agostino

THEORY Ecotoxicology is a study of the effect of toxic chemicals on biological organisms. It’s interdisciplinary field between ecology and toxicology. The Organization of economic cooperation and development (OECD) has guidelines to the specific tests which measure toxicity levels in organisms. The most important acute toxicity test is called LC50 – it is quantity of some substance that is fatal for 50% of tested population. The tests are usually performed on mice, other rodents and bees. The most important chronic toxicity test is EC50 – this is quantity of some substance that causes adverse affects on 50% of tested population.

VIBRIO FISCHERI Vibrio fischeri is a bacterium, found in marine environments. It has bioluminescent properties. It is a heterotrophe. It is found in all oceans of the world. The are found in higher concentrations in symbiosis with certain deep sea life withing special light organs. The bioluminescence is caused by transcription of the Lux operon, indected by population dependent a quorum sensing. The luminescence is seen only in unpolluted environment.

VIBRIO FISCHERI Lux operon is a functional unit of DNA that is controlled by single promotor. It controls light production. Quorum sensing is a system of simulae and response correlated to population density. A heterotrophe is an organism that uses organic carbon for growth. Symbiosis is cooperation between two or more organisms (of different spieces).

HYPOTHESIS The water at the spring of the Vipava river is less polluted than the water in Miren village, because human activity has not affected it yet. The water at the spring of the Vipava river is more suitable for the living environment of Vibrio Fischeri bacteria than the water near Miren village.

METHODS Equipment used: electronic pH meter scale magnetic stirrer and magnet spectrophotometer and computer test tubes pipettes cuvettes Reagents used: Water samples 1 & 2 NaCl NaOH (0,1M) HCl (0,1M) K 2 Cr 2 O 7

METHODS Procedure: Sampling at two different parts of the Vipava river. Once at the spring and second time at the lower part of the river (in village called Miren). Each time, three samples were taken. Adjusting pH and salinity of the samples in the laboratory in order to prepare optimal living conditions for the bacteria. Activating (unfreezing) the bacteria. Preparing solutions for measuring the luminescence with spectrophotometer. Spectrophotometry.

RESULTS

INHIBITION AFTER 15 MINUTES

INHIBITION AFTER 30 MINUTES

CONCLUSIONS Our toxicity test was valid. The first sample was less polluted/toxic and appropriate for the growth of the bacteria. Surprisingly, the bacteria felt better in the 1st sample than in the blank one. The bacteria emitted even more light when they were in the 1st sample therefore the inhibition was negative (nearly zero). That means that the bacteria felt really good in the new environment.

CONCLUSIONS The second sample was heavily polluted and inappropriate for the growth of the bacteria. After the bacteria were exposed to our sample for 15 minutes, the emmission of the light decreased for 33% - that means that 33% of the bacteria were inhibited (they died or did not feel well) After 30 minutes the bacteria emitted 37% less light than in the blank sample. The percentage didn’t increase very much, because the bacteria adjusted to the new conditions. Both hypothesis were confirmed.