Viable bacterial spores recovered from an archaeological excavation.

THERMOPHILIC actinomycetes grow rapidly and sporulate profusely in natural high temperature habitats such as composts, stored fodders and cereals. In these habitats can be found large numbers of Thermoactinomyces spp. endospores which exhibit longevity and extreme resistance to adverse conditions. Such spores have been recovered from lake muds and have been estimated to be more than 1,000 yr old, but it is important to have more accurate dating. For this purpose we have examined occupational debris from a Roman archaeological site which has been shown to be rich in plant debris and has been accurately dated from associated artefacts. Our findings show a strong correlation between viable spore count of Thermoactinomyces spp. and the nature of the substrate. We have also shown that it may be possible to undertake qualitative and quantitative analyses, using microbial taxa with specific environmental requirements, for archaeological interpretation. Furthermore, the study of evolutionary trends within the genus Thermoactinomyces is now possible.