Physiological changes of a green alga (Micractinium sp.) involved in an early-stage of association with Tetrahymena thermophila during 5-year microcosm culture

Germond, Arno; Kunihiro, Tadao; Inouhe, Masahiro; Nakajima, Toshiyuki

doi:10.1016/j.biosystems.2013.08.005

Cited by 15 publications

(21 citation statements)

References 22 publications

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“…SC9-1, SC10-2, SC10-3) would tend to be more easily ingested by the ciliate than the other types of cells. It was demonstrated that these non-aggregating algal isolates clones enhanced the longevity of a Tetrahymena clone when co-cultured in the absence of bacteria, suggesting that these algal clones developed an endosymbiotic phenotype (Germond et al, 2013;Nakajima et al, 2013). The aggregated form of the algal cells is likely to facilitate interactions with the bacterium by harbouring the bacterial cells within the aggregates.…”

Section: Rdna-based Identificationmentioning

confidence: 99%

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

Germond

Hata

Fujikawa

et al. 2013

European Journal of Phycology

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Recent phylogenetic studies of Chlorella-like algae revealed that this group has diversified into free-living and endosymbiotic niches, the latter within protists and invertebrate organisms. Our previous studies using a long-term culture composed of an alga (Chlorella vulgaris, rDNA sequence unknown), a bacterium (Escherichia coli) and a ciliate (Tetrahymena thermophila), suggested that some clones in the algal population developed an endosymbiotic ability with T. thermophila while others developed an ectosymbiotic ability with E. coli from a non-associated stage. In this paper, an rDNA (18S, ITS1, 5.8S, ITS2)-based phylogeny of the ancestral strain and derived clones isolated from 5-year microcosm cultures was constructed and revealed that the alga belongs to the genus Micractinium. This result was supported by analysis of the secondary structure of the rRNA gene. No difference was observed in the sequence between the ancestral and derived clones. On the other hand, some morphological and physiological traits of the ancestral strain and the derived clones were analysed and revealed that several phenotypic changes had occurred among the algal clones. In particular, the derived clones obtained from long-term cultures had increased in cell size, changed in their ability to grow at pH 4.0, and developed a tendency for cell-aggregation or sedimentation.

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Section: Rdna-based Identificationmentioning

confidence: 99%

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

Germond

Hata

Fujikawa

et al. 2013

European Journal of Phycology

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“…Genetic studies based on sequences of 18S and ITS regions (2700 bp length) showed no differences between the ancestral strains and 12 algal clones isolated from long-term microcosms (Germond et al, 2013a). Further studies using two algal clones (SC9-1 and SC10-2), isolated from within Tetrahymena cells, revealed that these clones released higher concentrations of glycerol and sucrose at pH 7.2 when compared with the ancestral strain at the same pH (Germond et al, 2013b). The release of carbohydrates and photopigment content were both correlated with the average cell size, larger for the isolated algal clones than for the ancestral strain, suggesting that selection favoured large cell size in symbiotic Micractinium (Germond et al, 2013b).…”

Section: Introductionmentioning

confidence: 99%

“…The composition and concentrations of sugar-alcohols and mono-, di-and oligo-saccharides were monitored by HPLC (Hitachi, Tokyo, Japan) following the procedures detailed in Germond et al (2013b). Pigment concentrations were related to cell densities at the time of harvest to estimate the cellular content.…”

Section: Determination Of Carbohydrate Concentrations In Acidic Condimentioning

confidence: 99%

“…Each filter was placed into a 15 ml sterilized tube and stored at −85°C prior to extraction. Pigments were extracted by the addition of 2.0 ml N,N dimethylformamide (DMF) and separated by high-performance liquid chromatography (HPLC) using the procedures and apparatus described in Germond et al (2013b), which were modified from those described in Takasu et al (2011). Pigment separation was performed with a ternary solvent system based on the report by Zepata et al (2000).…”

Section: Determination Of Photopigment Concentrations In Acidic Condimentioning

confidence: 99%

“…Further studies using two algal clones (SC9-1 and SC10-2), isolated from within Tetrahymena cells, revealed that these clones released higher concentrations of glycerol and sucrose at pH 7.2 when compared with the ancestral strain at the same pH (Germond et al, 2013b). The release of carbohydrates and photopigment content were both correlated with the average cell size, larger for the isolated algal clones than for the ancestral strain, suggesting that selection favoured large cell size in symbiotic Micractinium (Germond et al, 2013b). These findings suggest that a cooperative algal phenotype benefiting Tetrahymena evolved in the microcosm (Nakajima et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

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Effects of acidic conditions on the physiology of a green alga (Micractiniumsp.) before and after a 5-year interaction withTetrahymena thermophilain an experimental microcosm

Germond

Inouhe

Nakajima

2014

European Journal of Phycology

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The mechanisms through which algae evolve physiological characteristics related to endosymbiotic associations with heterotrophic organisms remain unclear. We previously showed that a green alga (Micractinium sp.) was able to evolve a host (ciliate)-benefiting phenotype that prolonged the longevity of Tetrahymena thermophila in the absence of bacteria during a 5-year culture period in an experimental microcosm. Comparative experiments between the ancestral alga (i.e. original) and evolved algal clones of the same lineage can be performed to analyse the mechanisms that underlie algal evolution during interactions with ciliates. Here, we investigated the effects of acidic conditions on algal physiology because the acidic conditions within the food vacuoles of Tetrahymena could potentially affect algal evolution during long-term interactions. It might be expected that algal clones isolated from T. thermophila hosts would have developed the ability to resist acidic conditions in order to establish within the host, when compared with the ancestral strain. Unexpectedly, comparative analyses demonstrated that acidic conditions with pH values ranging from 3.9 to 4.3 limited the growth of the isolated algal clones SC9-1 and SC10-2, whereas the ancestral strain could grow under these conditions. Acidic conditions were responsible for significantly lower chlorophyll a/chlorophyll b ratios in the isolated algal clones, and the isolated clone SC9-1 exhibited a high cellular content of chlorophyllide a during a short exposure to acidic conditions, suggesting that degradation of chlorophyll a occurred. Furthermore, acidic conditions increased the release of extracellular glycerol and sucrose in the SC9-1 clone. These results indicated that the ancestral strain showed phenotypic changes related to acidic conditions, which may reflect the ongoing development of an algal phenotype suited to symbiosis. Hypotheses are proposed to explain the limited growth of the isolated clones, and implications for the Micractinium-Tetrahymena association are discussed.

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Symbiotic Associations in Ciliates: Ecological and Evolutionary Perspectives

Germond¹,

Nakajima

2016

Biocommunication of Ciliates

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Physiological changes of a green alga (Micractinium sp.) involved in an early-stage of association with Tetrahymena thermophila during 5-year microcosm culture

Cited by 15 publications

References 22 publications

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

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

Effects of acidic conditions on the physiology of a green alga (Micractiniumsp.) before and after a 5-year interaction withTetrahymena thermophilain an experimental microcosm

Symbiotic Associations in Ciliates: Ecological and Evolutionary Perspectives

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