TITLE: Susceptibility of Microbes to Fuel in Salt Marshes
AUTHOR: Julie Ann Sautter
SCHOOL: Hanover High School
SCHOOL ADDRESS: Cedar Street, Hanover, MA

The susceptibility of microbial populations from soil horizon layers O1, O2, and A1 to varying concentrations of Diesel fuel, a petroleum-based secondary fuel, was compared between two salt marsh ecosystems. Soil cores from a non-polluted Scituate salt marsh and a polluted Boston Harbor slat marsh were taken and separated by horizon layer. Water samples were also taken. Microbes from these samples were streaked in thirds on agar-based petri dishes. Parts of each colony were taken from each of the six samples, grown in L broth as a layer, and divided it four tubes (for each site and a layer). The six control tubes contained only L broth. The three experimental groups had L broth and a particular concentration (0.2%, 0.02%, or 0.002%) of Diesel fuel. These 24 tubes were read for absorbency at 600 nm. On the spectrophotometer at 0, 60, 120, and 180 minutes. For the control group, the A1 microbes grew more than O2 microbes. Microbes closest to the water (O1) exhibited the least growth of all layers in these cultures. One can conclude that O1 microbes received more contact with the water, and were exposed to contaminants earlier than other layers. Water samples revealed more bacteria were present in the polluted site than in the non-polluted site. Boston salt marsh microbes exposed to fuel grew faster than Scituate microbes who received the same concentration of the pollutant. Boston's O1 microbes grew the best under the highest concentration (9.2%0 of Diesel fuel than the two layers below it. The O2 microbes in Boston grew the best under the middle concentration (0.02%) of fuel than the layer above the layer below it. The bottom layer (A1) microbes grew best under the lowest concentration (9.992%) of fuel. In Boston harbor, the microbes first exposed to pollution adapt to dealing with high levels of pollutants more so than the microbes in soil layers beneath it. Each layer protects the one beneath it form the same concentration that is faced with, almost a littering system. S the pollutant moves down in the soil, the concentration lessens, there for each layer adapts to a different level of pollution than the ones above and below it. Cultures grown without fuel or the Scituate site grew more than the cultures with the pollutant added. As the concentration of fuel increased, the growth rate of the Scituate microbes decreased in descending order form the top layer to the bottom layer. Inc conclusion, microbes exposed to more pollution in their natural habitat have evolved defense mechanisms, enabling them to live in less favorable environments as compared with those who have not had a high exposure to many contaminants.