Pochvenniye Vodorosly Fitotsenozov Sakharo-Gobiyskoy Pustynnoy Oblasti

Lewin, Ralph A.

doi:10.2216/i0031-8884-20-3-315.1

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“…Studies of the 18S rRNA -based molecular phylogeny of didemnid ascidians indicate that photosymbiosis with Prochloron has occurred independently in each of these genera (Yokobori et al, 2006). Besides the unsuccessful attempts to cultivate Prochloron separated from its hosts, a symbiotic relation is supported, e.g., by observations of carbon and nitrogen exchange between Prochloron and host (Lewin and Pardy, 1981; Kremer et al, 1982; Griffiths and Thinh, 1983; Koike et al, 1993), light-enhanced growth of didemnids with Prochloron (Olson, 1986), and fascinating specializations in didemnids ensuring vertical transmission of Prochloron to ascidian larvae during maturation and before they leave the parent tunic (Hirose, 2009), i.e., the extracellular matrix of protein and cellulose-like carbohydrates, wherein the host zoids are embedded. However, the exact nature of the symbiosis and mutual benefits in the ascidian- Prochloron association is still poorly understood (Hirose and Maruyama, 2004).…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2012

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The discovery of the cyanobacterium Prochloron was the first finding of a bacterial oxyphototroph with chlorophyll (Chl) b, in addition to Chl a. It was first described as Prochloron didemni but a number of clades have since been described. Prochloron is a conspicuously large (7–25 μm) unicellular cyanobacterium living in a symbiotic relationship, primarily with (sub-) tropical didemnid ascidians; it has resisted numerous cultivation attempts and appears truly obligatory symbiotic. Recently, a Prochloron draft genome was published, revealing no lack of metabolic genes that could explain the apparent inability to reproduce and sustain photosynthesis in a free-living stage. Possibly, the unsuccessful cultivation is partly due to a lack of knowledge about the microenvironmental conditions and ecophysiology of Prochloron in its natural habitat. We used microsensors, variable chlorophyll fluorescence imaging and imaging of O2 and pH to obtain a detailed insight to the microenvironmental ecology and photobiology of Prochloron in hospite in the didemnid ascidian Lissoclinum patella. The microenvironment within ascidians is characterized by steep gradients of light and chemical parameters that change rapidly with varying irradiances. The interior zone of the ascidians harboring Prochloron thus became anoxic and acidic within a few minutes of darkness, while the same zone exhibited O2 super-saturation and strongly alkaline pH after a few minutes of illumination. Photosynthesis showed lack of photoinhibition even at high irradiances equivalent to full sunlight, and photosynthesis recovered rapidly after periods of anoxia. We discuss these new insights on the ecological niche of Prochloron and possible interactions with its host and other microbes in light of its recently published genome and a recent study of the overall microbial diversity and metagenome of L. patella.

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