Source: Laboratories of Dr. Ian Pepper and Dr. Charles Gerba - The University of Arizona Demonstrating Author: Bradley Schmitz Reverse transcription-polymerase chain reaction (RT-PCR) involves the same process as conventional PCR - cycling temperature to amplify nucleic acids. However, while conventional PCR only amplifies deoxyribonucleic acids (DNA), RT-PCR enables the amplification of ribonucleic acids (RNA) through the formation of complementary DNA (cDNA). This enables RNA-based organisms found within the environment to be analyzed utilizing methods and technologies that are designed for DNA. Many viruses found in the environment use RNA as their genetic material. Several RNA-based viral pathogens, such as Norovirus, and indicator organisms, such as pepper mild mottle virus (PMMoV), do not have culture-based detection methods for quantification. In order to detect for the presence of these RNA viruses in environmental samples from soil, water, agriculture, etc., molecular assays rely on RT-PCR to convert RNA into DNA. Without RT-PCR, microbiologists would not be able to assay and research numerous RNA-based viruses that pose risks to human and environmental health. RT-PCR can also be employed as a tool to measure microbial activity in the environment. Messenger RNA (mRNA) is the single-stranded template for protein translation, and measuring the levels of different mRNAs indicates which genes from which microbes are being expressed within the environment. Analyzing gene expression gives clues to what biological pathways are used by organisms to survive in different environmental conditions. In some cases, gene expression can be utilized to determine which organisms may survive best in harsh conditions and have capabilities for bioremediation of contaminated soil or water.