Ultrastructural and microspectrophotometric characterization of multiple species of cyanobacterial photosymbionts coexisting in the colonial ascidianTrididemnum clinides(Tunicata, Ascidiacea, Didemnidae)

Abstract

Trididemnum clinides is a multi-photosymbiotic ascidian that inhabits shallow coral reef lagoons. Three types of cyanobacteria are harboured in the tunic of the ascidian colony; of these, two are unicellular coccoid cyanobacteria and the other is a multicellular filamentous type. They also differ in ultrastructure and distribution patterns within the host tunic. Microspectrophotometric analysis revealed the composition of photosynthetic pigments in each photosymbiont. One of the coccoid types is yellowish-green and is distributed under the colony surface. This photosymbiont cell preferentially absorbs red and blue light, and therefore the dominant colour in the inner tunic is green. The other two types of coexisting photosymbionts contain the green-light-absorbing R-phycoerythrin as the major photosynthetic pigment; they exploit the wavelengths of light not used by the first type of photosymbiont. In T. clinides, the outer and inner photosymbionts in the tunic have different photosynthetic pigments, which adapt to each microhabitat, thereby sharing the incident light resources effectively.

Complex microbiome underlying secondary and primary metabolism in the tunicate- Prochloron symbiosis

“…Calothrix was also identified by Sanger sequencing of 16S PCR clone libraries. Filamentous cyanobacteria have previously been observed in Prochloron-bearing didemnids on several occasions, but not from L. patella (23)(24)(25)(26)(27)(28)(29). A few eukaryotic microbes, such as diatoms and dinoflagellates, were observed in L2 but not in L1 (Fig.…”

“…P. didemni thus allows didemnid ascidians to thrive in nutrient-poor, light-rich environments of the tropics. Didemnids have also been found to contain other types of microbes, but unlike P. didemni, without extensive in vivo functional studies (21)(22)(23)(24)(25)(26)(27)(28)(29).…”

Microenvironmental Ecology of the Chlorophyll b-Containing Symbiotic Cyanobacterium Prochloron in the Didemnid Ascidian Lissoclinum patella

“…The slower dynamics of O 2 in this layer is probably the result of light screening by cyanobacteria in the upper test and the Prochloron layer. Both zones of cyanobacteria have been observed before and the tunic is known to harbor the cyanobacterium Synechocystis trididemni and other cyanobacteria with special pigmentation (Lafargue and Duclaux, 1979; Kott, 1984; Cox et al, 1985; Hirose et al, 2009b; López-Legentil et al, 2011). López-Legentil et al (2011) found Chl d -containing Acaryochloris cells in the unic of other didemnid ascidians on mangrove roots in the Bahamas but we have not found any evidence for Chl d in the unic of L .…”

Origin and Variation of Tunicate Secondary Metabolites

“…These mostly include other cyanobacteria, 32-36 but also reports about other types of bacteria, especially proteobacteria. 37-40 In the course of sequencing the P. didemni genome, we obtained an immense amount of data concerning other bacteria as well.…”