How the sponge stays slim

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London, November 17 (ANI): In a new research, a team of biologists has discovered how a reef-dwelling species of sponge can filter enormous amounts of carbon without growing in size.

According to a report in Nature News, the research was done by Jasper De Goeij at the Royal Netherlands Institute for Sea Research in Texel, the Netherlands, and his colleagues.

The research revealed that the sponge Halisarca caerulea can absorb up to two-thirds of its own weight in carbon each day by shedding cells at a rapid rate.

The team proposes that this fast turnover may be a tactic for coping with the toxins and pathogens that are frequently encountered by the filter-feeders in their environment.

H. caerulea is found on tropical reefs in the waters of the Caribbean, and feeds by filtering carbon-rich organic matter from the water.

Earlier work by De Goeij had shown that the sponges could absorb prodigious amounts of carbon yet didn't seem to grow in size.

"We calculated that a sponge should double in biomass every three days, but found that H. caerulea hardly grows at all," said De Goeij.

To find out why, De Goeij and his colleagues collected growing sponges and stained them continuously with a chemical that labels actively dividing cells.

The team cut samples from the sponge bodies at different time points up to 10 hours after the first exposure and analysed them for signs of the labelling agent.

They found that certain cells that pump and filter water in the sponge divided very quickly - once every five hours or so.

But, adding a second chemical to search for dead cells revealed only a few in the chambers, which left them with a puzzle: the sponge wasn't growing, but the cells didn't seem to be dying off.

Each day, H. caerulea absorbs up to two-thirds of its weight in carbon.

De Goeij was stumped until he gave a presentation on the sponge's impressive cell division to a group of cancer researchers.

They immediately recognized the rapid division behaviour as being very similar to that of the human gastrointestinal tract.

Cells in the epithelium of the colon are replaced every 12-24 hours by rapid proliferation and then shedding.

"Once we looked at the sponge tissue with the human colon in mind, we found massive amounts of shedding," said De Goeij.

De Goeij and his colleagues suggest that the rapid growth and shedding of the cells may be an evolutionary response to the harsh conditions in which H. caerulea grows. (ANI)

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