Genetic Evidence of "American" and "European" Type Symbiotic Algae of Paramecium bursaria Ehrenberg

Abstract

Paramecium bursaria is composed of a "host" ciliate and a "symbiont" green alga. Based upon physiology, DNA hybridization and virus infection, two types of symbionts, called "American" type and "European" type, have been reported to date. Here, we determined the 18S rDNA and internal transcribed spacer 2 (ITS2) regions for both "American" and "European" types. Sequence features clearly separated into two lineages; NC64A (USA), Syngen 2-3 (USA), Cs2 (Chinese), MRBG1 (Australian), and Japanese strains belong to the "American", whereas PB-SW1 (German) and CCAP 1660/11 (British) strains belong to the "European". In "American" 18S rDNA, three introns were inserted in the same positions as for previously described Japanese symbionts. In "European" 18S rDNA, a single intron occurred in a different position than in the "American". Between the types, sequence differences were seven or eight nucleotides (0.39 %) in the 18S rDNA exon, and more than 48 nucleotides (19.2 %) in ITS2 regions. We subsequently sequenced the host 18S rDNA. As a result, two groups: Cs2, MRBG1, and Japanese strains, and PB-SW1 and CCAP 1660/11 strains, were separated (with 23 substitutions and 4 insertions or deletions between the groups). The congruent separations between hosts and symbionts may imply that the type of symbiont depends on the host type.

The phylogenetic position and phenotypic changes of a Chlorella-like alga during 5-year microcosm culture

“…Recent developments in reconstructing phylogenetic relationships between strains or species in Chlorellalike algae (Hoshina et al, 2005(Hoshina et al, , 2010Luo et al, 2006;Pröschold et al, 2011) not only provide an Table 3. Ability to use sugars and susceptibility towards antibiotics of the ancestral and derived algal clones isolated from the CET microcosm cultures.…”

“…The sequences were aligned using ClustalW or Muscle (in MEGA5: Tamura et al, 2011) and adjusted by eye, taking into consideration the secondary structures of ITS found using Mfold 3.2 (Mathews et al, 1999;Zuker, 2003). Intron regions of the SSU were completely removed as suggested by previous studies (Hoshina et al, 2005(Hoshina et al, , 2010Pröschold et al, 2011). There were a total of 56 sequences and 2522 unambiguously aligned base positions in the final dataset.…”

“…For example, it was believed that Paramecium bursaria harbours one algal lineage (e.g. Reisser, 1984), yet the North American ciliate strain contains different algal species from the European strain (Hoshina et al, 2005). Likewise, the same symbiotic species can associate with several different host species.…”

“…Recent rDNA-based phylogenetic analyses of Chlorella-like algae, including endosymbiotic and free-living (planktonic or edaphic) species, have revealed that endosymbiotic algae are polyphyletic, that a phylogenetic or macro-evolutionary pattern of these algae involves adaptive radiation into endosymbiotic and free-living niches, and that host-symbiont associations are not necessarily a one-to-one relationship but can involve one-to-many and many-to-one relationships (Hoshina et al, 2005;Pröschold et al, 2011). For example, it was believed that Paramecium bursaria harbours one algal lineage (e.g.…”

Siderocelis irregularis (Chlorophyta, Trebouxiophyceae) in Lake Tanganyika (Africa)

“…It has commonly been stated that the predominant symbiotic algal partners of freshwater associations belong to the genus Chlorella (with some preference to the Chlorella vulgaris-sorokiniana cluster) and its representatives do not differ principally by morphology or cytology from free-living chlorellae, but are distinguished from them mainly by physiological characteristics (Reisser & Widowski 1992). More recently, the first molecular phylogeny based on 18S rRNA sequences was reported and revealed paramaecian symbionts which were genetically close to so-called Chlorella vulgaris group (Hoshina et al 2004(Hoshina et al , 2005. Occasionally, other green algae (species of Scenedesmus, Ankistrodesmus, Pleurococcus, Oocystis, Choricystis, Chlamydomonas, Symbiococcum and a few prasinophyceans) have been reported to occur in freshwater symbiotic systems (for references consult Reisser 1984;Rahat 1992;Reisser & Widowski 1992;Nakahara et al 2004).…”