Deep Bacterial Biosphere in Marine Sediments
University of Bristol UK
Professor R.John Parkes
Thank you very much for that kind introduction. And it's a privilege to talk at this meeting especially having been introduced so well by other speakers and I hope that I don't disappoint you.
Could I have the first slide please?
The aim of my talk is to demonstrate the presence of deep bacterial populations in marine sediments including some environments where bacterial populations actually increase in deeper layers. This information is based on some twelve ocean drilling program sites in the Pacific and Atlantic Oceans, and also the Mediterranean Sea, some of which are shown on this slide (Fig.3). I'd like to also describe some of the possible controls on the depth of the deep marine biosphere, such as temperature, pressure, and age of the sediment, explain why a deep biosphere may be wide spread in marine sediments and should go much deeper than we have currently sampled. Also, I will describe some new bacteria isolated from this environment during experiments to simulate heating during sediment burial and demonstrate that subsurface life accounts for a substantial portion of the total biomass on our planet with implications for deep biosphere interactions including fossil fuel formation and the origin of life which actually may have occurred in the subsurface as well as near hydrothermal systems and the presence of deep biosphere's on other planets.
The results of satellite technology demonstrates that the surface biosphere on our own planet is very widespread (Fig.4). You can see the land surface with forests and also the oceans with phytoplankton blooms. Photosynthesis where light energy is trapped and made available for living organisms is considered essential for all life on our planet being ultimately the food for all life. And we look now for similar surface life on other planets. But at that scale we miss the very small and this slide shows (Fig.5) bacteria, which are all very small, with an average diameter of 1 micron, or a millionth of a metre, some 500 of which would go end to end across a human hair. Their cell shapes are very simple and it's very easy for these organisms to be overlooked. Recent research, however, demonstrates that they have a biomass, that means a total amount of cell mass in terms of carbon, that can be similar to that of all plants. And they are present in environments previously thought to be too extreme for life (Fig.6). For example, they can grow at extremes of temperatures as low as -5℃ all the way up to 113℃, as long as there is pressure to keep water liquid and these pressures can be quite enormous, greater than a 1000 atmospheres equivalent to at least 11km deep in the deepest part of ocean trenches. They can all grow under very acidic conditions from pH zero (including acidic conditions in the stomach, some bacteria actually cause ulcers which were previously thought not to be related to bacterial infection, but now that we recognise that it is ulcers can be successfully treated by antibiotics) all the way up to alkaline conditions. In these extreme conditions, it is only bacteria that can survive. In addition, bacteria were the first organisms to evolve on Earth, and 70% of the history of life on Earth has been solely bacterial and they've been responsible for developing the surface environment, including the formation of oxygen which is poisonous to many bacteria, called anaerobes, but essential to other life forms including us. But surprisingly anaerobic bacteria are still very important.
