A novel extracellular macromolecular system has been proposed based on the proteins containing ChW repeats [1]. ChW stands for Clostridial hydrophobic with conserved W (tryptophan). This repeat was originally described in Clostridium acetobutylicum but is also found in other Gram-positive bacteria including Enterococcus faecalis, Streptococcus agalactiae and Streptomyces coelicolor.

1: Genome sequence and comparative analysis of the solvent-producing bacterium Clostridium acetobutylicum. Nolling J, Breton G, Omelchenko MV, Makarova KS, Zeng Q, Gibson R, Lee HM, Dubois J, Qiu D, Hitti J, Wolf YI, Tatusov RL, Sabathe F, Doucette-Stamm L, Soucaille P, Daly MJ, Bennett GN, Koonin EV, Smith DR; J Bacteriol 2001;183:4823-4838. PMID:11466286