BONE-ASSOCIATED MICROBES: IMPLICATIONS FOR THE LONG-TERM STABILITY OF BONE IN TERRESTRIAL SYSTEMS

Bones are utilized across a range of disciplines and temporal scales to study modern and extinct vertebrates. Despite the importance of modern bone for forensics and fossil bone for paleontology, we know little about the microorganisms colonizing and potentially degrading the organic (collagen, DNA) and mineral (bioapatite) components of bone. A prior study of human DNA quantity and quality recovered from 165 bones from three skeletonized individuals demonstrated significant differences in DNA yield among bones within a single skeleton, but follow the same pattern between skeletons. As a first step in assessing the microbiological contributions to bone alteration and DNA degradation, we characterized bacterial and fungal communities colonizing the same bones previously examined for human DNA using Illumina MiSeq, and quantified bacterial DNA content using quantitative PCR (qPCR). Preliminary results indicate that bacterial communities of bones throughout the skeleton consist of Proteobacteria (20-35%), Actinobacteria (2-11%), Bacteroidetes (2-11%), Firmicutes (1-10%), with additional representatives of Verrucomicrobia, Planctomyetes, Chlamydiae, and Deinococus-Thermus. However, the proportion of these phyla and additional contributions from rarer taxa varies throughout the skeleton. For example, bones from the arm and hand contain a greater proportion of Firmicutes compared to other regions of the skeleton. Of the classified fungi, members of Ascomycota (40-60%) and Chytridiomycota (15-40%) dominate communities, with lesser representation of Basidiomycota. Initial results of qPCR range several orders of magnitude from 1.34 X 10³ in an intermediate cuneiform (foot) bone and 6.47 X 10⁷ in a scapula, which corresponds to high and low human DNA yield samples, respectively. These results provide novel insights into the diverse fungal and bacterial communities capable of colonizing bone, and suggest that enhanced microbial colonization results in organic (DNA) degradation. Taken together, these results indicate that microbially-mediated degradation of DNA, and potentially bioapatite, in modern bone is non-uniform across the skeleton. These early diagenetic processes set the stage for subsequent recrystallization, and are therefore critical to bone preservation over geologic time.