Temperature affects the host range of Rhabdochlamydia porcellionis and the infectivity of Waddlia chondrophila and Chlamydia trachomatis elementary bodies

The Rhabdochlamydiaceae family is a recent addition to the Chlamydiales order. 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 Chlamydiales order based on 16S rRNA encoding gene diversity. Unlike most chlamydia-like organisms, no Rhabdochlamydiaceae could be co-cultivated in amoebae and its host range remains largely unknown. Here, 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 a growth could initially only be obtained in the Sf9 cell line, lowering the incubation temperature of the mammalian cells from 37 {degrees}C to 28 {degrees}C allowed R. porcellionis to grow in those cells. Furthermore, a 6 h exposure to 37 {degrees}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 {degrees}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 {degrees}C than at room temperature. Our results demonstrate that members of the Chlamydiales adapt to the temperature of their host organism and that this adaptation can in turn restrict their host range. ImportanceThe Rhabdochlamydiaceae family is part of the Chlamydiales, a bacterial order that includes obligate intracellular bacteria sharing the same biphasic developmental cycle. This family have 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 Chlamydiales order, 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 {degrees}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 some chlamydiae adapt to the temperature of their reservoir, making a jump between species with different body temperatures unlikely.