A South-American Head Figure 2. Light and transmission electron microscopy of skin and soft tissues from TSA nu1: (a) 5 mm section from the skin on the edge of facial wound stained with Masson’s trichrome compared with contemporary skin (b); (c) semi-thin resin sections from the same area as (a) showing clearly visible nuclei in the epidermis. Note, bacteria and fungal hyphae on the surface; (d) biopsy from the neck region showing well-preserved muscle fibres with distinctive striations (Toluidine blue staining); (e) ultra-thin section showing desmosomes between two keratinocytes; (f) ultra-thin section showing well-preserved collagen and elastic fibres in the dermis. doi:10.1371/journal.pone.0002053.g002 Previous studies carried out on bone collagen and hair belonging to a 7–10 years old boy mummy found on Mount Aconcagua (Argentina), radiocarbon dated at 370670 years before present (BP), showed a d13C value of 210.8% and a d15N value of +10.4 % attributed to a predominantly maize based, non-marine diet [8]. In typical maize-based diets the d15N value, in bone collagen, ranges from 9.0 to 9.9 %. In bone collagen samples of Inca-related Sausas, the measured d15N ranged from 8 to 13% [9]. Earlier results [8] revealed that d15N values of hair are generally lower than for bone collagen [10]. The d13C value in our hair sample is consistent with a terrestrial diet (C3 plants) with a small but significant maize-based component (C4 plants) whereas the high d15N value could reflect an additional small marine component. To further support our contention that the concentrating power of bacteria that entered the hair post-mortem from the soil accounted for the high levels of metabolic toxic elements, we examined hair from a different mummy, also from South America, but buried in a different location. In this specimen the visual appearance of bio-films was indistinguishable from that of our subject’s hair but the elemental analysis showed high levels of different elements, in keeping with the proposition that the bacterial fauna in this burial site and the soil’s elemental content determined the results of the heavy metal concentration in hair (Table 2). Our hypothesis that the high levels of heavy metals in our subject’s hair were deposited by bacterial concentrating activity in bio-films has therefore some support. These toxic elements must have been deposited on the hair post-mortem by mechanism resembling those used by the bacterium Ralstonia mettalidurans to produce gold nuggets in some Australian gold mines [5]. Thus one explanation for the well-preserved tissues in our specimen is that extraordinary circumstances, bacterial growth and soil content of heavy metals conspired to preserve the tissues. Subsequently, this lead to inhibition of putrefaction normally PLoS ONE | www.plosone.org 3 April 2008 | Volume 3 | Issue 4 | e2053