Difflugia are testate Amoebae that use particulate inorganic matter to build a protective shell (generally called a test or theca). Difflugia globulosa were grown both in culture containing only naturally occurring theca building materials and under conditions where synthetic particles were present as well. The presence of particles, monodisperse Stöber silica microspheres of 1, 3 and 6 μm diameter or 4 μm polystyrene spheres, dramatically increased the rate of Difflugia growth, and foreign microspheres became the overwhelmingly dominant construction material. Optical and electron microscopy of the 6 μm particle studies revealed that Difflugia construct spherical vase-shaped thecae with strikingly reproducible composition, morphology and size. Time-lapse photography revealed construction techniques and masonry skills as Difflugia herded particles together, trapped them using phagocytosis, and applied the particles with bio-cement from inside the developing theca. The reported observations identify taxonomy complications, biomicrofabrication possibilities, and a discrete environmental impact of synthetic particle pollutants. The initial objective of this research was to produce monodisperse diatoms from which monodisperse silica microparticles (frustules) with complex and multiple-length-scale morphology could be prepared. Stöber particles were added as a diatom nutrient (silicic acid source). Our interest turned from monodisperse diatom preparation to the Difflugia after thecae became obvious and abundant in samples within two days of when the cultures were prepared with Stöber particles.

Amoebae assemble synthetic spherical particles to form reproducible constructs

2019 Fall National Meeting

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