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Abstract

The Chlamydiae are a phylum of obligate intracellular bacteria comprising important human and animal pathogens, yet their occurrence in the environment, their phylogenetic diversity and their host range has been largely underestimated. We investigated the seasonality of environmental chlamydiae in a Tyrrhenian coastal lake. By catalyzed reporter deposition fluorescence in situ hybridization we quantified the small planktonic cells and detected a peak in the abundance of environmental chlamydiae in early autumn with up to 5.9x104 cells ml-1 . Super-resolution microscopy improved the visualization and quantification of these bacteria, and enabled the detection of pleomorphic chlamydial cells in their protist host directly in an environmental sample. To isolate environmental chlamydiae together with their host we applied a high-throughput limited dilution approach and successfully recovered a Vexillifera sp., strain harboring chlamydiae (93% 16S rRNA sequence identity to Simkania negevensis), tentatively named 'Candidatus Neptunochlamydia vexilliferae'. Transmission electron microscopy in combination with fluorescence in situ hybridization was used to prove the intracellular location of these bacteria representing the first strain of marine chlamydiae stably maintained alongside with their host in a laboratory culture. Taken together, this study contributes to a better understanding of the distribution and diversity of environmental chlamydiae in previously neglected marine environments.