Already in 2007 Zalan Szabo showed that archaellum expression in Sulfolobus solfataricus is starvation induced. Lateron we showed that the same is true for S. acidocaldarius, but nothing was known about the mechanims behind this regulatory process.
To date we have identified 4 proteins that play a role in the control of archaellum expression. Most of them are termed Arn for Archaellum regulatory network:
ArnA and ArnB are repressor of archaellum expression as their deletion leads to hypermotile cells. ArnA contains a FHA domain and ArnB a vanWillebrand domain. Interestingly, both proteins were phosphorylated by two S. acidocaldarius kinases (Reimann et al, 2012).
The only serine/threonine phosphoatase (PP2A) in the S. acidocaldarius genome also seems to play an important role in this regulatory network, as its deletion also led to a hypermotile phenotype (Reimann et al., 2013).
ArnR is the so far only positive regulator of the archaellum. It is a membrane bound one component regulator that directly binds to two inverted repeats in the archaellum operon (Lassak et al, 2013). At the moment we are trying to understand how ArnR senses starvation stress to initiate archaellum expression. This work is currently funded by the CRC 746 in Freiburg.
In two recent papers (Bischof et al, 2019 a/b), we show an extensive analysis of the starvation response of S. acidocaldarius and a detailed analysis of ArnR and ArnR1.