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Cyanobacteria meet again

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A free-living cyanobacterium (above) lies next to its brethren from a distant past, now a chloroplast coiled up and trapped (for good) within a eukaryotic cell (bottom). The chloroplast still has remnants of the cyanobacterial genome, with a greatly reduced gene set. Both bacterial inner and outer membranes have also been retained — which is how both plastids and mitochondria usually have a double membrane. The most bacterial-like of the plastids belong to Glaucophytes, a small group of deep-branching algae. These plastids have retained the bacterial peptidoglycan (wall material) layer, between the two membranes. This, along with their vibrant blue-green colour, earns them a distinct name: cyanelles.

Pretty much every photosynthetic eukaryote you see shares one single common origin of plastid endosymbiosis, with the exception of a testate amoeba — Paulinella chromatophora, which has one or two recently reduced cyanobacteria (‘cyanelles’, again) of a separate origin. There is a relatively large interest (reads: a couple labs) in Paulinella in hopes that studying it will reveal something about how plastid endosymbiosis works, as well as some insights to how the other (main) symbiosis event happened. Eukaryotes have thus domesticated cyanobacteria on at least two separate occasions, and seem to be doing fairly well with their stolen agriculture industry.

Psi Wavefunction About the Author: Psi Wavefunction is a graduate student working with protists (the 'other' eukaryotes) at Dalhousie University in Halifax, Nova Scotia, and now blogs about protists and evolution at Skeptic Wonder. Follow on Twitter @Ocelloid.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. greenhome123 1:17 am 03/1/2013

    I am curious if Glaucophytes or cyanelles are edible? like spirulina, chlorella, and Klamuth blue green algae.

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  2. 2. Psi Wavefunction 12:08 pm 03/2/2013

    Good question! The commercially-viable edible algae tend to be multicellular (at least filamentous, like spirulina), and/or grow like a weed (Chlorella; Euglena — there’s a face mask in Japan containing that stuff, for some inexplicable reason). Glaucophytes aren’t very common in nature, or at least not found in a wide range of habitats. They may simply not grow fast enough to be of commercial interest — and I don’t think anyone has checked their toxicity either. You have to get huge vats of millions upon millions of cells in order to get some mass out of a single celled organism, and not every critter is interested in being cooperative in that.

    There are some attempts to mass-culture some brown algal relatives for omega-3-fatty acids though — like Thraustochytrids and Labyrinthulids. They secrete a ton of those, but the problem lies in growing them up in vast, stable quantities and then harvesting the compounds.

    It is tempting, after a few beers too many, to contemplate centrifuging various microbial cultures and tasting the pellet. Probably wouldn’t make the safety inspection people too happy though ;-)

    Oh, and whatever you do — don’t taste dinoflagellate cultures. Some can be deadly toxic, causing paralytic shellfish poisoning (and Red Tide).

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  3. 3. greenhome123 1:47 pm 03/3/2013

    Thanks for the detailed response. I definitely won’t go taste testing any dinoflagellate cultures, but I’m still hopeful that Glaucophytes could be grown for human consumption in near future. I just did search for the glaucophyte, Cyanophora paradoxa, and it looks like its genome has been sequenced, and it is classified as a living fossil. I also did many searches for glaucophytes, cyanophora paradoxa, and toxin – and it doesn’t look like there is any mention of cyanophora paradoxa or any glaucophytes having any toxins, although I realize that doesn’t necessarily mean it isn’t toxic. On somewhat related note I recently read that salamanders and Newts have algae living inside their cells as an endosymbiont, which could possibly have something to do with their ability to regenerate limbs. The force is strong with those amphibians :-)

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