Symbiont life history and host range

In a Russian-German-Italien collaboration lead by Martina Schrallhammer, we have published anarticle in FEMS Microbiology, investigating  phylogenetic position, life-history characteristics and host range of a bacterial symbiont ofParamecium.
Alexey Potekhin, Michael Schweikert, Irina Nekrasova, Valerio Vitali, Sabine Schwarzer, Arina Anikina, Oliver Kaltz, Giulio Petroni, Martina Schrallhammer. 2018. Complex life cycle, broad host range and adaptation strategy of the intranuclearParameciumsymbiontPreeria caryophilacomb. nov.,FEMS Microbiology Ecology,
Holosporaand related bacteria are a group of obligateParameciumsymbionts. Characteristic features are their infectivity, the presence of two distinct morphotypes, and usually a strict specialization for a singleParameciumspecies as host and a nuclear compartment (either somatic or generative nucleus) for reproduction.Holospora caryophilasteps out of line, naturally occurring inParamecium biaureliaandParamecium caudatum.This study addresses the phylogenetic relationship amongH. caryophilaand otherHolosporaspecies based on 16S rRNA gene sequence comparison analysing the type strain and seven new macronuclear symbionts. Key aspects ofHolosporaphysiology such as infectivity, symbiosis establishment, and host range were determined by comprehensive infection assays. Detailed morphological investigations and sequence-based phylogeny confirmed a high similarity between the type strain ofH. caryophilaand the novel strains.Surprisingly, they are only distantly related to otherHolosporaspecies suggesting that they belong to a new genus within the familyHolosporaceae, here described asPreeria caryophilacomb. nov. Adding to this phylogenetic distance, we also observed a much broader host range, comprising at least elevenParameciumspecies. As these potential host species exhibit substantial differences in frequency of sexual processes,P. caryophilademonstrates which adaptations are crucial for macronuclear symbionts facing regular destruction of their habitat.