Microbiome of Bone Mineral Microspheres: A Brief History on the Golgi-Directed Road to Force Translation and Geo/Biomorphological Evolution
The nature of intracellular bone salt is elusive. Its concentration and distribution are frequently fugitive to standard electron microscopy procedures, such that the inorganic phase of bone is widely reported as an extracellular precipitate of hydroxyapatite crystals epitactic on collagen and obedient to the laws of inorganic chemistry. Light microscopy, in contrast, captures the cyclical intracellular mineral loading of “switched on” osteocyte cohorts. Rapidly fabricated within their golgi apparatus are nascent microspheres, approximately 1 micron diameter, calcified with phosphate/carbonate and unloaded at the calcification front in a stress-related process also manifest in a silt-burrowing invertebrate. The calcified objects densely populating the bone matrix may be examined in situ or isolated for density fractionation analysis. They are variably tempered by Si, Mg, Al, K, Na, Fe, stain histochemically for acid phosphatase, bone sialoprotein, osteocalcin encapsulation, osteopontin and nucleic acids, are Gram stain positive for microbes and form a fluorescent complex with the antibiotic tetracycline. They occur discretely, or in chains and bridged assemblies, tending to be smaller than average in osteoporosis, and larger in osteoarthritis. The substructure of the electron dense, deformable objects is complex, each composed of 5nm thick beaded filaments clustered around a less dense centre. Their archetype occurs in calcifying prokaryotes (e.g., Spirostomum ambiguum), also in microbes (e.g., Corynebacterium matruchotii), and in sedimentary rocks mined as fertiliser. The evidence suggests that bone mineral microspheres constitute a geo/biomorphological microbiome of ancient bionts colonising a hierarchical cancellous microcosm of periosteal force translation.
