When the submersible Alvin explored the deep ocean trenches around the Galápagos Islands in 1973, it discovered a whole new ecosystem centred around the geothermal vents; fumaroles or chimneys which spouted boiling hot water from deep inside the earth’s crust. Micro-organisms called extremophiles thrived there: bacteria and a whole new ‘domain’ of life known as the archaea that were able to survive the extreme pressures and temperatures at those depths in the absence of sunlight, drawing energy directly from the earth’s crust and utilising oxygen dissolved in sea water. Other extremophiles have been discovered in the subzero rocks and ice in Antarctica and also in highly acidic or alkaline volcanic lakes. This was life but not as we knew it and it changed our perspective. If life could exist is these extreme environments, then it could also exist in the hostile environments of other solar planets. Geothermal vents probably exist under the ice crust of Europa, one of the moons of Jupiter. Archaea could also be present in rocks in the polar regions of Mars. They can even withstand fragmentation of their RNA caused by extreme radiation in space. Suddenly Fred Hoyle’s speculation that bacteria could have colonised the earth as passengers on meteorites does not seem so far fetched. Archaea on rocks even survive the heat of re-entry on the outside of space shuttles. Such observations and speculations have fuelled a new science; astrobiology, once the provenance of science fiction.
But Archaea do not only exist in hostile environments, enormous numbers are present in the plankton rich ocean currents, in the soil, in biofilms and slimes and notably in the human colon. Archaea possess properties that make them very resistant. The cell membrane phospholipid structure is based on ethers rather than esters, making it more rigid, their RNA exists in a single large chromosome, that can fragment and recombine, and even transfer their genes between different organisms and species.
Little is known about the Archaea in the colon. They are not as prevalent as bacteria and have tended to be ignored by scientists. Since they have not been specifically implicated in human disease, most gastroenterologists are unaware of their existence. The Archaeic species that have been recognised in the human colon are all methanogens; they utilise excess hydrogen together with methanol or acetate to generate methane, which may have an important role in regulating colonic function. In the colons of mice, methane has been shown to slow transit and cause constipation. This would allow time for the same slowly replicating methanogens to bloom and build up concentrations of methane that might further slow transit. So once constipation develops it can quickly become established unless radical treatment is applied to flush out the colonic contents and start again.
The Archaeic methanogens are resistant to conventional antibiotics, but populations are decimated by statins. Although governments in both the United States and Britain have encouraged the use of statins to reduce cholesterol levels and the incidence of heart attacks, we have yet to find out what effect this will have on colonic health. Refined diets, low in fibre, slow colonic transit and are associated with increased methanogenesis and constipation. Conversely, high protein diets rich in sulphur amino acids (eggs, meat, poultry and fish), encourage the growth of sulphate reducing bacteria which provide an alternative hydrogen sink and inhibit methanogens, and, as described in my recent post on meat fermentation, they produce a range of indoles, phenols and hydrogen sulphide which sensitise and irritate the colon.
It is likely in the next few years, microbiologists will discover a diversity of Archaeic life both on our nearest planets and in our colon. What, I wonder, will be the implications of all this? Beam me up, Scotty!