THE ROLE OF BACTERIALLY MEDIATED PRECIPITATION IN THE PERMINERALIZATION OF BONE

Bone fossilization is generally thought to be predominantly slow and geochemically controlled, whereas soft-tissue preservation is rapid and microbially enhanced. Microbial destruction of bone has been well researched, but potential preservational influences of microbes on bone are relatively unstudied. Building on previous work, this study examined evidence for microbially induced mineralization of bone buried in a simulated terrestrial setting using an actualistic, experimental approach designed to allow both biotic and abiotic precipitation to occur. Four trials were conducted in 2002 by burying bleached fresh bone cubes in river sand through which calcium carbonate saturated water was percolated. A “natural” trial used unmodified river sediment with natural bacterial populations. Two trials were run with bleach or sodium azide to reduce or eliminate bacterial populations. A fourth trial used washed, bleached sediment with reintroduced bacteria. After one week, the natural trial showed signs of mineral precipitation that cemented sand grains to the bone cubes. Bones from both the natural and washed trials were completely covered by adherent sediment after six weeks. After twelve weeks, cancellous bone in the nonsterile trials was permineralized while antiseptic trials and compact bone showed no indications of permineralization. Nonsterile trials also exhibited partially calcified fungal hyphae and possible lithified bacteria. This study provides additional experimental evidence that microbes are important agents of fossilization for bone as well as soft tissue. It also supports the inference that microbially induced mineral precipitation can play a significant role in bone fossilization by enhancing bone survival through early permineralization until apatite recrystallization occurs.