Abstract
Paramecium bursaria (Ehrenberg 1831) is a ciliate species living in a symbiotic relationship with green algae. The aim of the study was to identify green algal symbionts of P. bursaria originating from distant geographical locations and to answer the question of whether the occurrence of endosymbiont taxa was correlated with a specific ciliate syngen (sexually separated sibling group). In a comparative analysis, we investigated 43 P. bursaria symbiont strains based on molecular features. Three DNA fragments were sequenced: two from the nuclear genomes—a fragment of the ITS1-5.8S rDNA-ITS2 region and a fragment of the gene encoding large subunit ribosomal RNA (28S rDNA), as well as a fragment of the plastid genome comprising the 3′rpl36-5′infA genes. The analysis of two ribosomal sequences showed the presence of 29 haplotypes (haplotype diversity Hd = 0.98736 for ITS1-5.8S rDNA-ITS2 and Hd = 0.908 for 28S rDNA) in the former two regions, and 36 haplotypes in the 3′rpl36-5′infA gene fragment (Hd = 0.984). The following symbiotic strains were identified: Chlorella vulgaris, Chlorella variabilis, Chlorella sorokiniana and Micractinium conductrix. We rejected the hypotheses concerning (i) the correlation between P. bursaria syngen and symbiotic species, and (ii) the relationship between symbiotic species and geographic distribution.
Highlights
The unicellular ciliate Paramecium bursaria (Peniculia, Oligohymenophorea) is a host of endosymbiotic algal species
Results of the analysis of ITS1-5.8S-rDNA-ITS2, 28S rDNA and 30 rpl36-50 infA chloroplast gene fragments revealed similarity of the isolated strains to the species described as Chlorella vulgaris, Chlorella variabilis, Chlorella sorokiniana and Micractinium conductrix
Results of the analysis of the ITS1-5.8S rDNA-ITS2 fragments (543 bp) of 37 endosymbionts revealed the existence of 29 haplotypes in the studied dataset
Summary
The unicellular ciliate Paramecium bursaria (Peniculia, Oligohymenophorea) is a host of endosymbiotic algal species. The mutualistic symbiosis exhibited by P. bursaria suppresses the genetic change of the inhabitant and ensures a nutritionally stable environment. Doebeli and Knowlton [1] reported that the rate of nucleotide substitutions was lower in symbiotic algae than in free-living relatives and their corresponding inhabitants since their co-evolution from an ancient association. Each syngen in Bomford’s collection (which was lost) had specific geographical distributions. Based on some similarities between syngens from the “old” and “new” collections, it has been suggested that syngen R1 is widespread in Europe; syngen R2 is widespread in Europe, extending eastwards to Siberia and Australia; syngen R4 is fairly widespread in the USA; and syngen
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