independent

Sunday 25 August 2019

'Star Jelly' far from being extra-terrestrial

JIM HURLEY

ONE OF the consequences of the exceptionally wet summer we have been experiencing is the abundance of a life form called Nostoc. It presents as blobs of green jelly that fade rapidly into a brown smelly mess.

In the past the sudden appearance of the strange blobs of green jelly was ascribed to an extra-terrestrial source. There is a very old legend that claims that the material falls to Earth after a meteorite shower. Indeed its popular name is ' star-jelly'. Nostoc is a rather severe-sounding name; star-jelly has a nicer ring to it.

Scientists too had difficulty pigeon-holing the unusual jelly; early on it was believed to a plant, then it was classified an alga or slime mould, nowadays it is assigned to a group of bacteria.

Nostoc is a very ancient group of bacteria that is believed to have evolved earlier than 570 million years ago. Members of the group are related to the strange-looking stromatolites found in Australia, Brazil, Mexico and the Bahamas.

Nostoc bacteria are extremely common but since they are microscopic in size they go un-noticed. They belong to a large group of life forms called cyanobacteria. These are harmless, free-living bacteria that are often blue-green in colour and that make their own food via photosynthesis in the way grass does. Members of the group are found in soil and in plankton both in freshwater and in seawater.

Some of the best-known cyanobacteria are the highly visible ones that cause the so-called ' algal blooms', extensive scums of green material in both in freshwater and in seawater.

Nostoc lives underground in the soil. While its body is a tiny single cell, cells regularly join together to make long chains like a necklace. They also irregularly clump together to form gelatinous lumps like green wine gums and hollow balls about the size of a green grape. However, being hollow the lumps usually collapse into irregular shapes. In wet weather these green, jelly-like lumps come above the surface of the ground and cover the surface in an amazing display.

Nostoc has the ability to fix atmospheric nitrogen in the soil so it plays a major role in soil fertility. The swollen star-jelly normally erupts from very wet grass after periods of prolonged heavy rain so it is the exceptionally wet summer that caused its recent appearance. I've also seen it on gravel and earthen paths in an old walled garden and on an old tarmac farmyard.

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