Observations on the theca of the motile phase of free-living and symbiotic isolates of<i>Zooxanthella microadriatica</i>(Freudenthal) comb.nov.

Loeblich, Alfred R.; Sherley, James L.

doi:10.1017/s0025315400046270

Cited by 127 publications

(80 citation statements)

References 17 publications

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“…Symbiodinium spp. belong in the family Symbiodiniaceae, which has been recently included in the order Suessiales (Fensome et al, 1993) based on ultrastructural data (Loeblich & Sherley, 1979), and was subsequently supported by rDNA data (Saunders et al, 1997;Montresor et al, 1999). The divergence of Symbiodiniaceae from Polarella glacialis Montresor, the only other cultured Suessiale, has been estimated at~200 Mya (Montresor et al, 1999).…”

Section: Discussionmentioning

confidence: 95%

Highly organized structure in the non-coding region of the psbA minicircle from clade C Symbiodinium

Moore

2003

INTERNATIONAL JOURNAL OF SYSTEMATIC AND EVOLUTIONARY MICROBIOLO

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The chloroplast genes of dinoflagellates are distributed among small, circular dsDNA molecules termed minicircles. In this paper, we describe the structure of the non-coding region of the psbA minicircle from Symbiodinium. DNA sequence was obtained from five Symbiodinium strains obtained from four different coral host species (Goniopora tenuidens, Heliofungia actiniformis, Leptastrea purpurea and Pocillopora damicornis), which had previously been determined to be closely related using LSU rDNA region D1/D2 sequence analysis. Eight distinct sequence blocks, consisting of four conserved cores interspersed with two metastable regions and flanked by two variable regions, occurred at similar positions in all strains. Inverted repeats (IRs) occurred in tandem or 'twin' formation within two of the four cores. The metastable regions also consisted of twin IRs and had modular behaviour, being either fully present or completely absent in the different strains. These twin IRs are similar in sequence to double-hairpin elements (DHEs) found in the mitochondrial genomes of some fungi, and may be mobile elements or may serve a functional role in recombination or replication. Within the central unit (consisting of the cores plus the metastable regions), all IRs contained perfect sequence inverses, implying they are highly evolved. IRs were also present outside the central unit but these were imperfect and possessed by individual strains only. A central adenine-rich sequence most closely resembled one in the centre of the non-coding part of Amphidinium operculatum minicircles, and is a potential origin of replication. Sequence polymorphism was extremely high in the variable regions, suggesting that these regions may be useful for distinguishing strains that cannot be differentiated using molecular markers currently available for Symbiodinium. INTRODUCTIONUnigenic DNA minicircles of 2-3 kbp that encode plastid gene functions have been found in a number of different peridinin-containing dinoflagellates, including species of Heterocapsa (Zhang et al., 1999(Zhang et al., , 2002, Amphidinium operculatum (Barbrook & Howe, 2000;Barbrook et al., 2001), Amphidinium carterae (Hiller, 2001) and Protoceratium reticulatum (Zhang et al., 2002). The non-coding regions of the minicircles are highly divergent across dinoflagellate genera, except that short stretches of a single nucleotide are frequent. A common format across dinoflagellate genera and species is that the non-coding regions contain conserved core regions, usually of between two and four in number, separated by variable regions (Zhang et al., 2002;Howe et al., 2003). In a given species, two or more cores are often identical to each other, seemingly duplicated or triplicated within the same minicircle, such as the two 9G regions of Heterocapsa triquetra (Zhang et al., 1999(Zhang et al., , 2002, and the three 5G regions of Heterocapsa pygmeae (Zhang et al., 2002).It has been shown that conserved core regions are shared between all the minicircles present in one culture of Abbreviat...

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Section: Discussionmentioning

confidence: 95%

Highly organized structure in the non-coding region of the psbA minicircle from clade C Symbiodinium

Moore

2003

INTERNATIONAL JOURNAL OF SYSTEMATIC AND EVOLUTIONARY MICROBIOLO

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“…The relationship is clearly of benefit to the coral (and is indeed obligatory for reefbuilding species), but the degree of benefit and dependence to the zooxanthellae is less clear (Douglas and Smith 1989), since almost nothing is known about the ecology and physiology of free-living zooxanthellae in the natural environment (LaJeunesse 2001). Although most hosts acquire zooxanthellae from the environment, free-living strains have only rarely been isolated (Loeblich and Sherley 1979;Carlos et al 1999).…”

Section: Zooxanthellaementioning

confidence: 99%

Multispecies Microbial Mutualisms on Coral Reefs: The Host as a Habitat

Knowlton

Rohwer

2003

The American Naturalist

411

307

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Reef-building corals associate with a diverse array of eukaryotic and noneukaryotic microbes. Best known are dinoflagellates in the genus Symbiodinium ("zooxanthellae"), which are photosynthetic symbionts found in all reef-building corals. Once considered a single species, they are now recognized as several large, genetically diverse groups that often co-occur within a single host species or colony. Variation among Symbiodinium in host identities, tolerance to stress, and ability to colonize hosts has been documented, but there is little information on the ecology of zooxanthellar freeliving stages and how different zooxanthellae perform as partners. Other microbial associates of reef corals are much less well known, but studies indicate that individual coral colonies host diverse assemblages of bacteria, some of which seem to have species-specific associations. This diversity of microbial associates has important evolutionary and ecological implications. Most mutualisms evolve as balanced reciprocations that allow partners to detect cheaters, particularly when partners are potentially diverse and can be transmitted horizontally. Thus, environmental stresses that incapacitate the ability of partners to reciprocate can destabilize associations by eliciting rejection by their hosts. Coral bleaching (the loss of zooxanthellae) and coral diseases, both increasing over the last several decades, may be examples of stress-related mutualistic instability.

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“…Even though Trench and Blank (1987), Loeblich andSherley (1979), andFreudenthal (1962) described motile forms of S. kawagutii and S. microadriaticum, they were not observed in this study because of the difference in cultivating condition.…”

Section: Discussionmentioning

confidence: 54%