Modeling the effects of acid rain on bacterial growth

Abstract

Acid rain has caused devastating decreases in ecosystems across the globe. This problem has been escalating due to the burning of fossil fuels. To mimic the effect of acid rain on the environment, we analyzed the growth of gram-negative (Escherichia coli) and gram-positive (Staphylococcus epidermidis) bacteria in agar solutions with different pH levels. We tested the hypothesis that agar with higher concentrations of vinegar would inhibit growth of gram-negative and gram-positive bacteria. We used agar with no bacteria as the negative control to ensure that there was no contamination of the agar from the environment. After 7 days at 25°C, we measured the size and number of the bacterial colonies. Our results showed that there was growth of both bacteria in each of the different agar concentrations, while the control agar exhibited no growth. The growth of the Escherichia coli (E. coli) colony was much greater than from the Staphylococcus epidermidis (S. epidermidis) colony at 3 different concentrations of vinegar: 6.25% Vinegar, 12.5% Vinegar, and 25% Vinegar. 6.25% Vinegar models current conditions in lakes while 25% represents future models at the rate we are going. While both bacteria grew in all solutions, there was clear evidence that more growth was visible in the agar with less vinegar. Also, measurement of the growth of each bacterium with daily check-ups over the week-long study showed the bacteria grew quicker in the agar with no vinegar. These results show that in a given acidic environment there was a significant decrease in bacterial growth with an increase in vinegar concentration in the agar, suggesting that bacterial growth is impacted by the pH of the environment. Therefore, increased levels of acid rain could potentially harm the ecosystem by altering bacterial growth.