bacteria that cannot be grown. By using functional libraries, the gene functions of unculturable bacteria can still be studied. Furthermore, these uncultured microbes provide a source for the discovery of novel enzymes with biotechnological applications. Some novel proteins that have been discovered from marine environments include enzymes such as proteases, amylases, lipases, chitinases, deoxyribonucleases and phosphatases. Determining homology in a known species There are situations in which it is imperative to determine if a gene homolog from one source is present in another organism. For example, identification of novel DNA polymerases for polymerase chain reaction (PCR) reactions which synthesize DNA molecules from deoxyribonucleotides. While human polymerase optimally works at 37 °C (98.6 °F), DNA does not denature until 94–98 °C (201–208 °F). This poses a problem as at these temperatures the human DNA polymerase would denature during the denaturation step of the PCR reaction resulting in a non-functioning polymerase protein and a failed PCR. To combat this a DNA polymerase from a thermophile, or bacteria that grows at high temperatures, could be used. An example is Taq polymerase which comes from the thermophilic bacterium Thermus aquaticus. One could set up a functional cloning screen to find homologous polymerases that have the added advantage of being thermostable at high temperatures. With this in mind, 3173 Polymerase, another polymerase enzyme, now commonly used in RT-PCR reactions was discovered using the above theory. In RT-PCR reactions, two separate enzymes are commonly used. The first is a retroviral reverse transcriptase to convert RNA to cDNA. The second is a thermostable DNA polymerase to amplify the target sequence. 3173 Polymerase is able to perform both enzymatic functions resulting in a better option for RT-PCR. The enzyme was discovered using functional cloning from a viral host originally found in Octopus hot springs (93 °C) in Yellowstone National Park. Human health applications One of the ongoing challenges of treating bacterial infections is antibiotic resistance which commonly arises when patients do not take their full treatment of medication and hence allow bacteria to develop resistance to antibiotics over time. To understand how to combat antibiotic resistance it is important to understand how the bacterial genome is evolving and changing in healthy individuals with no recent usage of antibiotics to provide a baseline. Using a functional cloning-based technique, DNA isolated from human microflora were cloned into expression vectors in Escherichia coli. Afterwards, antibiotics were applied as a screen. If