Temperature Affects the Host Range of Rhabdochlamydia porcellionis.

The Rhabdochlamydiaceae family is a recent addition to the Chlamydiae phylum. Its members were discovered in cockroaches and woodlice, but recent metagenomics surveys demonstrated the widespread distribution of this family in the environment. It was, moreover, estimated to be the largest family of the Chlamydiae phylum based on the diversity of its 16S rRNA encoding gene. Unlike most Chlamydia-like organisms, no Rhabdochlamydiaceae member could be cultivated in amoebae, and its host range remains unknown. We tested the permissivity of various mammalian and arthropod cell lines to determine the host range of Rhabdochlamydia porcellionis, the only cultured representative of this family. While growth could initially be obtained only in the Sf9 cell line, lowering the incubation temperature of the mammalian cells from 37°C to 28°C allowed the growth of R. porcellionis. Furthermore, a 6-h exposure to 37°C was sufficient to irreversibly block the replication of R. porcellionis, suggesting that this bacterium either lost or never acquired the ability to grow at 37°C. We next sought to determine if temperature would also affect the infectivity of elementary bodies. Although we could not purify enough bacteria to reach a conclusive result for R. porcellionis, our experiment showed that the elementary bodies of Chlamydia trachomatis and Waddlia chondrophila lose their infectivity faster at 37°C than at room temperature. Our results demonstrate that members of the Chlamydiae phylum adapt to the temperature of their host organism and that this adaptation can in turn restrict their host range. IMPORTANCE The Rhabdochlamydiaceae family is part of the Chlamydiae, a phylum of bacteria that includes obligate intracellular bacteria sharing the same biphasic developmental cycle. This family has been shown to be highly prevalent in the environment, particularly in freshwater and soil, and despite being estimated to be the largest family in the Chlamydiae phylum is only poorly studied. Members of the Rhabdochlamydiaceae have been detected in various arthropods like ticks, spiders, cockroaches, and woodlice, but the full host range of this family is currently unknown. In this study, we showed that R. porcellionis, the only cultured representative of the Rhabdochlamydiaceae family, cannot grow at 37°C and is quickly inactivated at this temperature. A similar temperature sensitivity was also observed for elementary bodies of chlamydial species adapted to mammals. Our work demonstrates that chlamydiae adapt to the temperature of their reservoir, making a jump between species with different body temperatures unlikely.