Thermus thermophilus HB27c

This strain is our lab workhorse. The origin of the HB27c strain is unknown; we initially assumed it was the previously described HB27c, but whole-genome sequencing revealed several differences. Notably, the HB27c pTT27 megaplasmid carries a ~25 kbps insertion encoding genes responsible for nitrate reduction. In addition, the HB27c pTT27 megaplasmid harbours an insertion that disrupts the gene encoding the prokaryotic Argonaute protein (TtAgo).

We prefer HB27c because it grows faster than HB27. HB27c also forms fine round colonies on plates (good for the visualization purposes), whereas HB27 frequently produces colonies with a stepped profile and serrated margins.

HB27c is naturally competent and can be readily transformed with plasmids carrying a Thermus-compatible origin of replication and a suitable resistance marker. Its transformation efficiency is higher than that of HB27, possibly owing to the absence of TtAgo. Importantly, HB27c is, for reasons that remain unclear, more susceptible to phage infection (at least by the Zuza27 and Lalka phages). I can only say that the phage susceptibility is not linked to the absence of TtAgo (we have checked this).