Plant Cuttings

Cyanobacteria: Good week, or bad week..? Part I

This is the first of what is hoped to be a series in which Mr P. Cuttings looks at a group of organisms and tries to decide whether they’ve had a good week, or a bad week. And by way of increasing the intrigue this initial instalment will be published as four separate blog posts, the first of which provides some necessary scene-setting and context.

Image: Kelvinsong / Wikipedia

Blue-green background

Cyanobacteria are intriguing organisms that appear to defy taxonomic pigeon-holing. On the one hand, they are bacteria, prokaryotic cells with a simple level of organisation with minimal internal organelles and no membrane-bound nucleus. On the other, cyanobacteria (or as I prefer to call them blue-green algae (BGs) thereby emphasising their bacterial uniqueness, and permitting their legitimate study by algologists) are like miniature – but extremely compact! – versions of eukaryotic green algae and land plants, because they photosynthesise* using Chlorophyll a (e.g. Lars Björn et al., 2009), water and carbon dioxide, to produce sugars and oxygen**.

BGs also have a dual nature from an ecological point of view. As important members of the phytoplankton community, most species are rather benign – and life-promotingly beneficial – in contributing massively to the productivity of the oceans via their photosynthetic efforts. This helps to promote and sustain complicated food webs in those aquatic environments. Others – BBGs (‘bad’ blue-greens) – however, are rather harmful because of the various so-called secondary products, secondary compounds, or secondary metabolites they produce. Although apparently harmless to the blue-greens that make them, these compounds (such as cylindrospermopsins (CYNs) and saxitoxins (STXs)) can cause harm and even death to a multitude of other aquatic organisms – and humans – who ingest those toxic cyanobacteria. This unintended consequence of feasting on the BBGs – whether directly and deliberately, or indirectly and inadvertently – is a particular concern when the cyanophytes occur in such large numbers that they are referred to as harmful algal blooms (HABs)***.

Two pieces of research news underline those dual characteristics of cyanobacteria: See Parts II and III of this series of posts.

* Although other bacteria photosynthesise, but the oxygenic – green plant-like – version is unique to cyanobacteria amongst those prokaryotic microbes.

** Further compounding their distinction from bacteria, and emphasising their ‘plantness’, cyanobacteria store a form of starch, and feature cellulose and pectin in their cell walls. That an ancient form of cyanobacterium is the likely precursor for the eukaryotes’ photosynthetic organelle known as the chloroplast is yet another reason…

*** For more on HABs, there’s a special issue of the appropriately named journal Harmful Algae devoted to articles about them.

Cyanobacteria: Good week or bad week?

Part I: Blue-green background
Part II: DOM, a double-edged sword…
Part III: Asteroids, bad for dinosaurs, but good for cyanobacteria?
Part IV: Cyanobacteria lighting the way for fossil fuel alternatives

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