Pseudomonas aeruginosa is a highly successful nosocomial pathogen capable of causing a wide variety of infectionswithclone C strains most prevalentworldwide. In this study, we initially characterize a molecular mechanism of survival unique to clone C strains. We identified aP.aeruginosa clone C-specific genomic island (PACGI-1) that contains the highly expressed small heat shock protein sHsp20c, the founding member of a novel subclass of class B bacterial small heat shock proteins. sHsp20c and adjacent gene products are involved in resistance against heat shock.Heat stable sHsp20c is unconventionally expressed in stationary phase in a wide temperature range from 20 to 42 degrees C. PurifiedsHsp20c has characteristic features of small heat shock protein class B as it is monodisperse, forms sphere-like 24-meric oligomers and exhibits significant chaperone activity. As theP.aeruginosaclone C population is significantly more heat shock resistant than genetically unrelated P.aeruginosa strains without sHsp20c, the horizontally acquired shsp20c operon might contribute to the survival of worldwide-distributed clone C strains.