Geochemistry

Shielding Bacteria

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Science  07 Sep 2001:
Vol. 293, Issue 5536, pp. 1731-1733
DOI: 10.1126/science.293.5536.1731e

Archean bacteria living about 2.5 billion years ago needed to be able to withstand high levels of UV irradiation because of the lack of atmospheric oxygen as a UV screen. Many early bacteria may have survived in a deep marine environment where the water provided UV shielding. However, there is evidence in the geological record of microbial mats and stromalites that inhabited shallow water environments, which would require some other means of UV protection.

Phoenix et al. placed cultures of cyanobacteria isolated from the Krisuvik hot springs, Iceland, in a silicon-and iron-rich solution. Rims of iron-enriched silica formed around the cells, and the cultures were then exposed to UV irradiation. Cells continued to grow within the mineralized rims even under intense UV. Thus, biomineralization may have helped the simplest forms of life to thrive in the intense sunshine of the Archean. — LR

Geology29, 823 (2001).

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