Chlorella variabilis and Micractinium reisseri sp. nov. (Chlorellaceae, Trebouxiophyceae): Redescription of the endosymbiotic green algae of Paramecium bursaria (Peniculia, Oligohymenophorea) in the 120th year

Abstract

Chlorella variabilis and Micractinium reisseri sp. nov. (Chlorellaceae, Trebouxiophyceae): Redescription of the endosymbiotic green algae of Paramecium bursaria (Peniculia, Oligohymenophorea) in the 120th yearp re_579 188..201 SUMMARY Symbiotic algae of the ciliate Paramecium bursaria (Ehrenberg) Focker are key species in the fields of virology and molecular evolutionary biology as well as in the biology of symbiotic relationships. These symbiotic algae were once identified as Zoochlorella conductrix Brandt by the Dutch microbiologist, Beijerinck 120 years ago. However, after many twists and turns, the algae are today treated as nameless organisms. Recent molecular analyses have revealed several different algal partners depending on P. bursaria strains, but nearly all P. bursaria contains a symbiont belonging to either the so-called 'American' or 'European' group. The absence of proper names for these algae is beginning to provoke ill effects in the above-mentioned study areas. In the present study, we confirmed the genetic autonomy of the 'American' and 'European' groups and described the symbionts as Chlorella variabilis Shihira et Krauss and Micractinium reisseri Hoshina, Iwataki et Imamura sp. nov., respectively (Chlorellaceae, Trebouxiophyceae).

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 genus Micractinium was composed of 27 operational taxonomic units (OTUs) and was distinct from the genus Chlorella (sensu stricto) (14 strains): separation of the genera was supported by high bootstrap values in all statistical analyses (ML, NJ, MP and ME). The Micractinium clade contained representatives of three named Micractinium species -Micractinium pusillum (for which Micractinium pusillum CCAP 248/5 is the authentic strain), Micractinium reisseri (Hoshina et al, 2010;Hoshina, 2011) and Micractinium belenophorum (a recently transferred species, Pröschold et al, 2011) -as well as several unnamed Micractinium species or lineages. The phylogeny placed the microcosm's ancestral algal strain (formerly described as C. vulgaris) within a group of Micractinium strains in the Chlorella clade (Fig.…”

“…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.…”

“…As molecular markers we used the rDNA gene (SSU 18S, ITS1, 5.8S and ITS2) and the secondary structure of the rRNA ITS2 region, as proposed in recent studies (Luo et al, 2006(Luo et al, , 2009Hoshina et al, 2010;Pröschold et al, 2011). For comparison, we also sequenced some strains from the NIES culture collection (Micractinium pusillum NIES-151, Micractinium sp.…”

Size of Paramecium bursaria individuals under cold and dark conditions

“…The green ciliate Paramecium bursaria is one of the best-studied protists because of its observable endosymbiosis. The photobiont species found in P. bursaria are almost exclusively either Chlorella variabilis or Micractinium reisseri (Chlorellaceae, Trebouxiophyceae) (Hoshina et al 2010;Pröschold et al 2011, and references therein). When isolated from P. bursaria cells in a laboratory, these two algal species excrete at least half of their photosynthate (maltose), as calculated from total carbon fixation (e.g., Reisser 1984;Kessler et al 1991;Kamako & Imamura 2006).…”