Bacterial biofilms as fossil makers(ons block autolysis and that embryos pre...)

Date:11/24/2008

ons block autolysis, and that embryos prevented from autolyzing are quickly colonized by marine bacteria. Once inside, the bacteria form biofilms that fill the embryo cells. Sturdy cell membranes and the embryo's fertilization envelope provide the exterior cast. These biofilms formed detailed replicas of the embryos they had replaced.

Species of the common marine bacterium Pseudoalteromonas provided the majority of the bacterial flora present inside the embryo cells under aerobic conditions. Under oxygen-poor conditions, a much greater diversity of bacterial species was present, not detectable under aerobic conditions.

The scientists also examined oxygen-starved embryos exposed to inoculums of oxygen-poor marine mud, and again found a high diversity of bacterial flora present in embryo replica biofilms, with species of the Bacteroidetes phylum being most common.

Although it is impossible to know whether bacteria aided the preservation of 550-million-year-old embryo fossils from Doushantuo and elsewhere, the Raffs argue the evidence they gathered strongly favors the view that bacteria are a fundamental force in fossil formation, as rapid biological processes must be available to convert highly delicate cells into a stable form and catalyse mineralization.

"This work is important because it helps us understand fossilization as a biological as well as geological process," Elizabeth Raff said. "It gives us a window onto the evolution of the embryos of the earth's first animals."

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Contact: David Bricker brickerd@indiana.edu 812-856-9035 Indiana University Source:Eurekalert

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