Primordial Earth Most Likely Was Populated by Numerous Colonies of Arsenic-Eating Bacteria

Examples of "lowly bacteria found in a foul-smelling hot spring near Mono Lake, California is a living window into Earth’s early history, a time when photosynthesis was barely evolved and the atmosphere non-existent."

Image: Science

The photos above provide evidence that: "Arsenic(III) Fuels Anoxygenic Photosynthesis in Hot Spring Biofilms from Mono Lake, California."

Science Magazine has written that: "Phylogenetic analysis indicates that microbial arsenic metabolism is ancient and probably extends back to the primordial Earth. In microbial biofilms growing on the rock surfaces of anoxic brine pools fed by hot springs containing arsenite and sulfide at high concentrations, we discovered light-dependent oxidation of arsenite [As(III)] to arsenate [As(V)] occurring under anoxic conditions. The communities were composed primarily of Ectothiorhodospira-like purple bacteria or Oscillatoria-like cyanobacteria. A pure culture of a photosynthetic bacterium grew as a photoautotroph when As(III) was used as the sole photosynthetic electron donor. The strain contained genes encoding a putative As(V) reductase but no detectable homologs of the As(III) oxidase genes of aerobic chemolithotrophs, suggesting a reverse functionality for the reductase. Production of As(V) by anoxygenic photosynthesis probably opened niches for primordial Earth's first As(V)-respiring prokaryotes."

That points to the discovery of: "A new kind of photosynthesis that uses arsenic instead of water to harvest light promises to rewrite evolutionary history - at least that of arsenic metabolism on Earth.

It is well known that: "The evolution of efficient, oxygen-based photosynthesis has been hard to explain. Primitive forms gathered energy from light by using it to free electrons from sulphur and iron in an oxygen-free environment. Oxygenic photosynthesis, which involves freeing electrons from water, takes more energy and produces oxygen. But oxygen was deadly to most primitive life on Earth. "The first organisms to do this would die," says Hyman Hartman of the Massachusetts Institute of Technology." This realization has lead some scientists to look to arsenic using bacteria as an answer to this vexing problem because "arsenic metabolism could have evolved much earlier, giving plenty of time for bacteria to diversify."

"Some bacteria use arsenate (a deadly poison) - arsenic with four oxygen atoms attached - as an energy source. It was thought that this form of metabolism didn't get going until long after photosynthesis filled the atmosphere with oxygen about 2.7 billion years ago. When this happened, naturally occurring arsenite would be transformed into arsenate."

"Ronald Oremland and colleagues at the US Geological Survey in Menlo Park, California," believe "arsenic metabolism could have evolved much earlier, giving plenty of time for bacteria to diversify."

"Mono Lake in California, USA NASA Landsat 7 image," Furthermore: "In the warm, bubbling pools of Mono Lake in California, scientists have isolated a bacterium that fuels itself on arsenic."

The team of American scientists explained: "Once you spit out oxygen, all kinds of things arise," said Ronald Oremland, a United States Geological Survey biogeochemist and co-author of the bacteria’s description, published today in Science. "It’s Part One of the evolution of Earth."

Regarding Mono Lake, which lies near the Sierra Nevada mountain range, Dr Oremland explained: "These lakes are fed by hydrothermal waters that leach out arsenic-containing minerals from the surrounding rocks."

The arsenic fueled bacteria "had colonised small, hot pools, forming colourful "biofilms"."

Dr Oremland explained their findings: "We suspected that these bacteria were using arsenic to make a living, so we scraped the biofilms off the rock and studied them under laboratory conditions."

Bacteria living in Mono Lake, California can survive the high levels of arsenic. BBC NEWS

The original study
T.R. Kulp, S.E. Hoeft, M. Asao, M.T. Madigan, J.T. Hollibaugh, J.C. Fisher, J.F. Stolz, C.W. Culbertson, L.G. Miller, R.S. Oremland, Arsenic(III) Fuels Anoxygenic Photosynthesis in Hot Spring Biofilms from Mono Lake, California, Science, 321 (2008) 967-970. DOI: 10.1126/science.1160799