Role of biomineralization as an ultraviolet shield: Implications for Archean life

Cyanobacteria, isolated from the Krisuvik hot spring, Iceland, were mineral ized in an iron-silica solution and irradiated with high levels of ultravio let light. Analysis of the rates of photosynthesis, chlorophyll-a content, and phycocyanin autofluorescence, revealed that these mineralized bacteria have a marked resistance to UV compared to nonmineralized bacteria. Natural ly occurring sinters composed of iron-silica biominerals collected from the Lysuholl hot spring, and made into wafers of 150-250 mum thickness, also p rovided cyanobacteria with an effective UV screen. Analysis of the UV-absor bing capacity of these wafers showed that they absorbed an order of magnitu de more UV than photosynthetically active light (required for photosynthesi s). From these results, it is evident that both natural and experimental bi omineralization provide bacteria with an effective UV screen through the pa ssive precipitation of iron-enriched silica crusts. The UV-shielding capaci ty of iron-bearing silicate biominerals may have been important for early l ife forms. We propose that the biomineralization of Archean bacteria simila rly provided protection from the high-intensity UV present at that time, an d hence allowed colonization and bacterial diversification of shallow-water environments.