The thermophilic bacterium Moorella thermoacetica possesses an rsb operon that is related to the genetic locus common to many Gram-positive bacteria that regulates the activity of the stress-responsive sigma factor sigma(B). One of the gene products of this operon is RsbS, a single STAS-domain protein that is a component of higher order assemblies in Bacillus subtilis known as 'stressosomes'. It is expected that similar complexes are found in M. thermoacetica, but in this instance regulating the biosynthesis of cyclic di-GMP, a ubiquitous secondary messenger. Selenomethionine-labelled MtRsbS protein was crystallized at room temperature using the hanging-drop vapour-diffusion method. Crystals belonging to space group P2(1)2(1)2(1), with unit-cell parameters a = 51.07, b = 60.52, c = 89.28 A, diffracted to 2.5 A resolution on beamline I04 of the Diamond Light Source. The selenium substructure was solved using SHELX and it is believed that this represents the first reported ab initio crystal structure to be solved using diffraction data collected at DLS.