Heat Shock Proteins in Mycoplasma

I was surprised to find that Mycoplasma genitalium has a rather elaborate heat-shock protein system. The details are in "Transcriptional Heat Shock Response in the Smallest Known Self-Replicating Cell, Mycoplasma genitalium," (J Bacteriol. 2006 April; 2845–2855) by Oxana Musatovova, Subramanian Dhandayuthapani, and Joel B. Baseman.

What's surprising about this is that Mycoplasma genitalium, an obligatory parasite, lives in a carefully temperature-controlled environment (the human body) that rarely fluctuates more than a couple degrees. Heat shock is not something Mycoplasma genitalium sees a lot of.

Because it is extraordinarily well-adapted to an unvarying habitat rich in nutrients, M. genitalium (like other Mycoplasma species) has shed many unneeded genes over its evolutionary history. The genome for M. genitalium is only 580K base-pairs long, with fewer than 500 open reading frames. Its genome is stripped to the bare minimum. For an organism this stripped-down to have a robust hsp system is remarkable.

It suggests that "heat shock proteins" are playing a crucial role even in the most minimalistic proteome.