VPE 511: Environment and Environmental Hygiene (2+1)

IRON BACTERIA

• Certain of the Bacteria have the power of abstracting iron from the water in which they live and of depositing it in the form of ferric hydroxide in the mucilagenous sheath with which they are invested.
• The “ochre-beds” sometimes seen on boggy moorland streams are produced by the deposition of the iron impregnated sheaths of these bacteria, which sink to the bottom of the stream when the bacteria die.
• The presence of iron in their surrounding medium is not essential to the life of the Iron Bacteria, for they can flourish in its absence.
• The iron seems to be assimilated by the bacteria probably in the form of ferrous bicarbonate, along with nutrient materials, is oxidised to the insoluble hydrated ferric oxide, and is then deposited in this form in the filament sheaths of the bacteria.
• Crenothrix is perhaps the best known of the Iron Bacteria, though possibly it is not the most widespread.
• As normally found, it consists of minute filaments attached by one end to some solid object.
• Each filament consists of a single row of cells, the whole being invested by mucilagenous sheath.
• Rapid multiplication of Crenothrix in supply reservoirs has occasionally produced spectacular effects in the water drawn from the service main. The water was unusable for domestic supply owing to its bad taste and smell.
• The effect in water supply systems due to Gallionella, another of the Iron Bacteria, is less striking than those of Crenothrix, but this organism in probably far more widespread.
• Gallionella forms a slimy coating on the inner surface of iron supply pipes, from which streamers extend into the water; this coating may become so thick that it considerably reduces the capacity of the pipes, Gallionella also plays a part in the formation of the hard rusty nodules and incrustations that are commonly seen in water-pipes in some areas.
• The exact role of the bacteria in the production of these is uncertain, but it is thought that in some way they accelerate the deposition of rust, probably through their oxidation processes.
• Chlorination of the water is one of the remedies that have been found satisfactory in the control of Iron Bacteria and the troubles arising there from in public supply systems.