Killer bacteria survive on ocean bed

Posted: 21 December 2000

The deepest parts of the ocean, once thought to be cold, dead zones, are in fact home to dormant bacteria and other biological material, recent research has shown. Despite pressures of many hundreds of atmosphere, temperatures close to freezing and total darkness, bacteria have been found in samples taken from the ocean bed more than 3,000 feet below the surface.

Scientists suspect that currents may occasionally disturb these deposits, raising columns of infected water that may cause epidemics in coastal areas. One such outbreak affected Bangladesh in 1992, when thousands were afflicted by a deadly new strain of cholera.

Dr Rita Colwell, Director of the US National Science Foundation, believes that this outbreak was linked to changes in sea-surface temperatures near the coast. "It appears that this bacteria was being sustained in the sea in plankton colonies which started to grow rapidly," said Dr Colwell. "When this happened, coastal communities were affected and from there the disease spread."

Other scientists have found evidence of human rubbish - such as tomato pips - appearing on the ocean bed, and bacteria resistant to antibiotics. Dr Colwell and others believe that ocean circulation - possibly affected by climate change - is sweeping nutrients to the surface, causing plankton-infected microbe to grow rapidly. This same upwelling could also bring bacteria to the surface.

In another development, toxic chemicals have been found in tissue samples taken from sperm whales - which only feed in the deep ocean - indicating that the pollutants have spread globally and settled in the ocean depths. The chemicals are polybrominated compounds - which cause many of the same effects as PCBs yet have not been banned. They are believed to cause fertility problems in animals by disrupting the balance of sex hormones in the body. Industry manufactures about 100,000 tons of the compounds every year, and production is expected to increase in the current decade.