Bacterial biofilms as fossil makers( BLOOMINGTON Ind. -- Bacterial decay ...)

BLOOMINGTON, Ind. -- Bacterial decay was once viewed as fossilization's mortal enemy, but new research suggests bacterial biofilms may have actually helped preserve the fossil record's most vulnerable stuff -- animal embryos and soft tissues.

A team of 13 scientists led by Indiana University Bloomington biologists Rudolf and Elizabeth Raff found that the invasion of dying embryo cells by bacteria -- and the subsequent formation of densely packed bacterial biofilms inside the embryo cells -- can completely replace embryo cell structure, generating a faithful replica of the embryo. The scientists call this formation a "pseudomorph," a model of the embryo made of bacteria. Their report will appear online via the Proceedings of the National Academy of Sciences "Early Edition" as early as Nov. 24.

"The bacteria consume and replace all the cytoplasm in the cells, generating a little sculpture of the embryo," said Elizabeth Raff, the report's lead author. "We did find, however, that certain conditions must be met if the bacteria are going to aid the preservation process."

Among those conditions, Raff said that at the time of its death, the embryo must exist in a low-oxygen or reducing environment, such as the bottom of a deep ocean or buried in anoxic lakeside mud. If significant oxygen is available, the embryo will undergo "autolysis," or self-destruction, as digestive enzymes get free and wreak havoc. Without oxygen, autolytic enzymes remain stuck inside their organelle prisons.

"The next step, we believe, is that bacteria able to survive in low-oxygen conditions must then infest the cells of the dying embryo," Raff said.

The bacteria form biofilms, crowded assemblies of bacterial cells held together by sticky fibers made of proteins and sugars. As the biofilms fill the embryo cells, the tiny bacteria insinuate themselves between and among the organelles, forming a faithful representation of the cell's innards.'/>"/>