In the 1930s, the Navajo Nation Treated Sheep and Cattle

In the 1930s, the Navajo Nation treated sheep and cattle for ticks and other parasites by using concrete "dip tanks," a common practice in the United States during that time period. Animals were herded into one end of the tank and out the other. Each day, the tanks were filled with 200,000 gallons of insecticide, and any remaining chemicals were emptied onto the ground. The pesticide solution seeped into the ground, ditches, and pits around the tanks.
In the 1990s, the EPA Emergency Response Team (ERT) was called to the Navajo Nation to investigate the problem. They concluded that bioremediation procedures were the best option for cleaning up the site. Certain types of bacteria are able to feed on and digest toxic organic substances, such as pesticides, and use them as fuel for cell respiration. The ERT distributed these pesticide-eating microorganisms throughout the contaminated soil to remove the chemical residues. Once the contaminants are degraded, these microorganism populations will die off because they will have used up all of their food supply.
-The bacteria used in this bioremediation procedure are

A) chemoautotrophs.
B) photoautotrophs.
C) chemoheterotrophs.
D) photoheterotrophs.