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How do Foraminifera build their shells?

Foraminifera are single-celled organisms, whose shells can have extremely elaborate shapes. Researchers, including scientists from Kraków, took a sneak peek at the cellular mechanisms that allow Foraminifera to add new "rooms" to their capsule apartments. This research inspires the creation of materials of the future.


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People need a device like a 3D printer to build a small, thin, three-dimensional structure of any shape. And not only is 3D printer imprecise, not every shape can be conveniently printed on it, it also requires heating the material to a high temperature. Meanwhile, single-celled aquatic organisms - Foraminifera - have been masters of such tasks for hundreds of millions of years. They produce their shells called tests with extremely sophisticated shapes with micrometre precision, and without melting the material - at ambient temperature.

"If we understood how these organisms are able to precisely build microstructures, we could use them to create materials or devices of the future" - says Prof. Jarosław Tyszka from the Institute of Geological Sciences of the Polish Academy of Sciences, Research Centre in Kraków, who researches Foraminifera.

Foraminifera colonized 70 percent of the Earth`s surface. They live on the bottoms of oceans and seas. Foraminifera cell builds a test - calcareous or glued with sand grains. A characteristic element of such a shell is a hole or multiple holes (hence the name of this group of organisms: Foraminifera, Latin for "hole bearers"). Through this hole, this cell has contact with the outside world and releases pseudopods to move, monitor its surroundings and find food. When the Foraminifera grows, it needs a larger "flat". It adds larger chambers to its test, and then larger still to them. Foraminifera tests can measure from 20 micrometres to 12 cm.

Different types of Foraminifera can organize their "house construction" in various ways, which is why the variety of shapes of tests is overwhelming. "Foraminifera have come up with all the solutions we can imagine and model" - believes palaeontologist Prof. Jarosław Tyszka. He adds that these organisms had a lot of evolutionary time - they have been on Earth for over 500 million years.

The research of his team (which included German and Dutch researchers and a Polish scientist from AGH-UST) on the cellular mechanisms of test building by Foraminifera was published in the prestigious journal PNAS.

"Until now, it was not known which molecular structures were responsible for the formation of these shapes. We have shown that they include the actin mesh. It creates dynamic matrices controlled by the body. They are responsible for the test shapes characteristic for a given species" - Prof. Tyszka summarizes the research. He adds that for the first time the formation of a test formed by a scaffold from the actin cytoskeleton has been observed on a living organism: a tiny architect was caught while building its "apartment".

Some scientists believed that Foraminifera produce the test directly on the outside of the cell, without covering it with cytoplasm (a fragment of the cell). "Our research shows that biomineralisation takes place within the cell and is controlled by it thanks to actin lamellipodia. They are thin "rugs" produced by the cell that surround the biomineralisation sites, underneath which the mineral skeleton structures form" - the researcher describes.

He adds that if we were able to reproduce such organic rugs based on an actin matrix, we would be able to control the formation of microstructures. He mentions that this would allow to produce, for example, miniature devices or super-precise scaffolds for medical applications, including bone regeneration.

But Prof. Tyszka - as a micropaleontologist - is interested in Foraminifera for different reasons. The skeletons of Foraminifera living long ago are part of geological structures. Tests of these (and other) organisms form chalk.

Foraminifera fossils are geological "microcapsules of time". They allow palaeontologists to estimate the age of a given geological layer, determine the temperature of the seas and oceans and the climatic conditions that prevailed in the past.

The researcher explains that scientists find many malformed tests in the rocks. It is not entirely clear what was responsible for these defects. It may be influenced by some characteristic conditions: the presence of certain elements, pollutants or excessive salinity. Thanks to the research published in PNAS (financed with a grant from the National Science Centre), scientists gain the tools to examine at a molecular level how the work of a small builder changes under the influence of stressful environmental changes. This could allow to more accurately assess the conditions prevailing on Earth in particular periods in the past.

Source: PAP - Science in Poland, Ludwika Tomala