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McCall's World

Modern Haloarchaea live in hypersaline lakes, as here in San Francisco Bay. Their cells contain carotenoid pigments, presumably for UV protection, which explain the rich colours. Image: Modern Haloarchaea live in hypersaline lakes, as here in San Francisco Bay. Their cells contain carotenoid pigments, presumably for UV protection, which explain the rich colours they may display when in large concentrations).

Scientists claim to have revived 250 million year old bacteria preserved in salt.


Geoscientist 21.07 August 2011


A controversy sparked in 19991 has been re-opened by an article by Loewenstein2. Vreeland and Rosenweig1 claimed to have revived by culture bacteria trapped in salt cystals 250 million years old, from the Permian Salado Formation near Carlsbad, New Mexico. Two years later Fish and colleagues at Leicester University claimed to have extracted DNA from haloarchaea even older, up to 425 million years old.

The objections to these research findings were based on the likelihood of contamination and the fact that the salt was not primary. Further researches reported by Loewenstein2, based on salt extracted from 93 metres below the surface in 10,000 to 100,000 year-old saline deposits in Death Valley (California), have revealed 20 genera of Haloarchaea + few bacteria and Dunialella, an algal eukaryote, in huge quantities (>10,000 Dunialella and 100 million smaller prokaryotes can live in one millilitre of water!) within fluid inclusions. Culturing can with extreme difficulty revive less than 1% of samples tested – but five microbes were apparently brought back to life.

Bacterial cells deprived of nutrients get smaller, tiny and spherical, unlike at the surface, but apparently derived their nutrients from Dunialella – it is claimed that glycerol from one cell of the eukaryote could supply enough carbon to repair macromolecular damage for one miniaturised Archaea cell for 12 million years. Lowenstein is admirably cautious and believes much further research is needed about these processes, but he believes that fluid inclusions in salt may yet prove to be a ‘magnificent time capsule’, and that these researches obviously have a bearing on the possibility of finding traces of past primitive life in Martian surface brines.

References

  1. Vreeland, R.H., Rosenzweig, W.D. et al. Characterization of a 250-million year old halotolerant strain of Bacillus pantothenticus and an extreme halophile utilising two and threee carbon compounds as sources. Meeting of the American Society for Microbiology at Chicago.
  2. Lowenstein, T. 2011.Bacteria back from the brink. Thousand and million year old microbes found living in salt crystals. Could they exist on other planets. Earth. 56(4), 36-45.
Sahelanthropus tchadensis on display at Lausanne Natural History Museum. Image: Wikimedia Commons. Image: Sahelanthropus tchadensis on display at Lausanne Natural History Museum. Image: Wikimedia Commons.

Researchers have thrown the cat among the hominins with their latest papers


Bernard Wood (George Washington University) and Terry Harrison (New York University)1,2 have created controversy over the classification and status of early hominins from East African and Chad.

Three discoveries there are widely accepted as being between four and seven million years old. The oldest, Sahelanthropu (picture), is from Chad and the two younger species from Kenya and Ethiopia, are Orrorin and Ardipithecus. Orrorin is represented only by a femur, but comes from Baringo District (where I and others re-evaluated and re-named Leakey’s Lake Kamasia Beds, showing from field studies that they were of two widely different ages and separated by an unconformity)3.

The authors point out that the fossils used to build up the classification, and the argument that they are hominins (and hence our ancestors), could equally well represent now-extinct apes or hominins from dead-end lines. They argue that ‘parallel evolution’ should not be discounted. The emergence of hominid-like traits (e.g. upright stance) may have evolved independently.

Tim White (University of California) objects, saying the 4.4Ma Ardipithecus, a partial skeleton of which his team excavated, was ruled out as an ape by comparative studies published in 2009. Others support Wood and Harrison. In their favour, a 12Ma Asian find and supposed hominid was an orangutan ancestor, and Oreopithecus (7-8Ma) from the Mediterranean islands was later found to have been an ape. There is a history of radical revisions in this complicated palaeoanthropological field, so we can expect this controversy to rumble on.

References

  1. Wood, B, Harrison, T. 2011. The evolutionary context of the first hominins. Nature 470, 347.
  2. Bower, B. 2011. www.sciencenews.org
  3. McCall, G J H, Baker, B H, Walsh, J 1967. Late Tertiary and Quaternary sediments in the Kenya Rift Valley. In: ‘Background to Evolution in Africa’: Bishop, W W, & Clark, J D (eds.), University of Chicago Press, Chicago and London, 191-220.