A moderately thermophilic bacterial strain, Meiothermus ruber H328, can efficiently solubilize intact chicken feathers by aerobic cultivation at 55 °C for 6 days. The keratinolytic proteases extracellularly secreted by the strain were partially purified by an ultrafiltration system and a size-exclusion column chromatography, and thus were found to be two different sizes of macromolecules with an extremely high molecular mass like the sizes of virus and DNA (peak 1 fraction) and with a molecular mass of larger than 500 kDa (peak 2 fraction). They formed protein complex assemblies that were composed of multiple but different proteins. The peak 1 fraction showed more thermophilic characteristics than did the peak 2 fraction in temperature dependence and thermal stability. By contrast, they comparably showed extraordinary resistance to powerful denaturants, SDS at 30 % (w/v) and organic solvents (methanol, ethanol, acetonitrile, acetone, and chloroform) at 40 % (v/v) at 60 °C for 30 min. The extraordinary denaturant tolerance and the large molecular size of the keratinolytic protease complex assemblies suggest the possibility that those may be lipophilic and have the structure of partial membrane fractions, or membrane vesicles, which are exfoliated from the outer membrane of the cells.

The thermophilic bacterium Meiothermus ruber H328 aggressively degrades chicken feathers. When feathers were added to culture medium, the cells significantly exfoliated membrane vesicles from the outer membrane as observed by electron microscopy of ultrathin sections. This is the first report of membrane vesicle production associated with keratinolytic activity by Meiothermus sp.

Non-detergent sulfobetaines (NDSBs) are known to stabilize many proteins, and we have found that NDSBs, in particular NDSB-256, potently stabilize rn2 muscarinic acetylcholine receptor