Form and habitat

Beggiatoa is a colourless, primitive “sulphur bacterium” usually found in extreme environments such as ocean depths, oxygen-deficient muds and hot springs.  The bacteria grow as discs which although individually small (about 2 microns across *), usually multiply by simple division into filaments many cells long. Beggiatoa are motile, moving by a gliding motion and they often form large mats covering substantial areas of the aquatic substrate in which it live.  The mats are held together by secretions of polysaccharides (sticky starch-like chemicals), which often appear white due to the reflection of light.

 There are both fresh water and salt-water types and they are a frequent constituent of “sewage fungus”, a strong indicator of pollution by sewage.  They also occur in other environments which are high in organic matter and low in oxygen such as loch sediments and in intensive fish farms where the wastes from the fish are especially concentrated.

Nutrition & growth

Beggiatoa are termed chemotrophic which broadly means they derive energy for growth and division by using chemical energy from some fairly simple substances in their environment (unlike plants which need energy from sunlight or animals which break down other organisms to get their energy).  They can therefore live in some fairly extreme environments - without sunlight, with a paucity of nutrients and low oxygen levels.  Indeed, they tend to favour acid environments which are relatively low in oxygen (anoxic).  The bacterial mats they form are used to trap gases and other simple chemicals which they use in their nutrition.

Other key features

Although Beggiatoa are on the whole, thought to be mainly biologically benign, they have been associated with Black Band disease of corals.  Their detrimental biological effects with respect to Whitsand Bay are probably fall into two main areas:

Exclusion of other organisms by physical means - using the extensive mat structure. Impoverishment of the local bio-community by preventing the diffusion of nutrients and gases to and from the substrate on which they live – effectively starving other organisms out.  

The main browsers / predators of Beggiatoa are small, simple organisms such as protozoa.  Few higher organisms can withstand the extreme conditions - mainly worms living in the nearby mud (polychaetes and nematodes).  Beggiatoa therefore holds sway in a biological desert and is difficult to eradicate once established.

The sediment below the bacterial mats typically becomes populated by other chemotrophs, often producing by-products such as hydrogen sulphide which are toxic to higher life forms.  Some of these mud-dwelling microbes are known to turn fairly inert heavy metals such as mercury into extremely reactive and toxic organic forms.  (The risk here is probably extremely small, but should not be discounted).

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