Co-existence of multiple bacterivorous clevelandellid ciliate species in hindgut of wood-feeding cockroaches in light of their prokaryotic consortium

The hindgut of wood-feeding Panesthia cockroaches harbours a diverse microbial community, whose most morphologically prominent members are bacterivorous clevelandellid ciliates. Co-occurrence and correlation patterns of prokaryotes associated with these endosymbiotic ciliates were investigated. Multidimensional scaling based on taxa interaction-adjusted index showed a very clear separation of the hindgut ciliate samples from the ciliate-free hindgut samples. This division was corroborated also by SparCC analysis which revealed strong negative associations between prokaryotic taxa that were relatively more abundant in the ciliate-free hindgut samples and prokaryotic taxa that were more abundant in the ciliate samples. This very likely reflects the grazing behaviour of hindgut ciliates which prefer Proteobacteria, Firmicutes and Actinobacteria, causing their abundances to be increased in the ciliate samples at the expense of abundances of Euryarchaeota and Bacteroidetes which prevail in the hindgut content. Ciliate species do not distinctly differ in the associated prokaryotes, indicating that minute variations in the proportion of associated bacteria might be sufficient to avoid competition between bacterivorous ciliate species and hence enable their co-occurrence in the same host. The nearest free-living relatives of hindgut ciliates have a different pattern of associations with prokaryotes, i.e., alphaproteobacteria are predominantly associated with free-living ciliates while gammaproteobacteria with hindgut ciliates.