The phage-derived RNA polymerase PhiFa-44 was identified and characterized in vitro with the use of recombinant protein expression.
PhiFa-44 requires dsDNA as a template and divalent metal ions, particularly Mn²⁺ and Co²⁺. The optimal temperature for activity is 35-40°C, surprisingly below the optimal growth temperature of its host. However, the activity at the required temperature for the SCOPE platform (65°C) is still sufficient for the intended purpose.
The optimal pH for PhiFa-44 activity was found to be 6.7-8.6. PhiFa-44 can be used in the current SCOPE platform without affecting the assay, and it still maintains sufficient RNA polymerase activity to enable a one-pot reaction (SCOPEv2).
This newly developed one-pot reaction composition was verified on P. aeruginosa samples. P. aeruginosa is a pathogen that can cause a variety of infections, including respiratory infections, urinary tract infections, and sepsis, particularly in individuals with weakened immune systems (such as COPD patients).
The SCOPEv2 can detect its target within 30 minutes and can detect as little as 10 synthetic copies/µL. Detection of live organisms resulted in a detection limit of 2.5E0 colony-forming units (CFU) per µL, and 2.5E-3 CFU/µL if the sample is pre-boiled.
These results have been made into a draft manuscript and are already published as a chapter in a PhD thesis.