High‐temperature adapted primitive P rotochlamydia found in A canthamoeba isolated from a hot spring can grow in immortalized human epithelial HEp ‐2 cells

Abstract

Summary To elucidate how ancient pathogenic chlamydiae could overcome temperature barriers to adapt to human cells, we characterized a primitive chlamydia found in HS ‐ T3 amoebae ( A canthamoeba ) isolated from a hot spring. Phylogenetic analysis revealed the primitive species to be P rotochlamydia . In situ hybridization staining showed broad distribution into the amoebal cytoplasm, which was supported by transmission electron microscopic analysis showing typical chlamydial features, with inclusion bodies including both elementary and reticular bodies. Interestingly, although most amoebae isolated from natural environments show reduced growth at 37°C, the HS ‐ T3 amoebae harbouring the P rotochlamydia grew well at body temperature. Although infection with P rotochlamydia did not confer temperature tolerance to the C3 amoebae, the number of infectious progenies rapidly increased at 37°C with amoebal lysis. In immortalized human epithelial HEp ‐2 cells, fluorescence microscopic study revealed atypical inclusion of the P rotochlamydia , and quantitative real‐time polymerase chain reaction analyses also showed an increase in 16S ribosomal RNA DNA amounts. Together, these results showed that the P rotochlamydia found in HS ‐ T3 amoebae isolated from a hot spring successfully adapted to immortalized human HEp ‐2 cells at 37°C, providing further information on the evolution of ancient P rotochlamydia to the present pathogenic chlamydiae.

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