Gibbs et al. (2009) studied the phylogeny of Thermus isolates and found they fell into 8 clades. They then isolated the DNA polymerase I genes from 22 representatives and cloned the 8 most diverse genes (to represent the 8 clades) into an expression vector. They were able to purify the protein from six of these clones and examined their biochemical characteristics and suitability for PCR. They found that none was as thermostable as commercially available Taq polymerase and all had error-frequencies similar to those of Taq polymerase. They concluded that the initial selection of T. aquaticus for DNA polymerase purification was a fortuitous choice, although they suggest that simple mutagenesis procedures on other Thermus-derived polymerases should provide comparable thermostability for the PCR reaction.
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