IDENTIFICATION OF BACTERIAL ISOLATES OBTAINED FROM INTESTINAL CONTENTS ASSOCIATED WITH 12,000-YEAR-OLD MASTODON REMAINS

Mastodon (Mammut americanum) remains unearthed during excavation of an cient sediments usually consist only of skeletal material, due to post mortem decomposition of soft tissues by microorganisms. Two recent exc avations of skeletal remains in anoxic sediments in Ohio and Michigan, however, have uncovered organic masses which appear to be remnants of the small and large intestines, respectively. Macrobotanical examinat ions of the composition of these masses revealed assemblages of plant material radiocarbon dated to approximately 11,500 years before the pr esent and thought to be incompletely digested food remains from this e xtinct mammal. We attempted to cultivate and identify bacteria from th e intestinal contents, bone-associated sediments, and sediments not in proximity to the remains using a variety of general and selective med ia. In all, 295 isolates were cultivated, and 38 individual taxa were identified by fatty acid-methyl ester (FAME) profiles and biochemical characteristics (API-20E). The taxonomic positions of selected enteric and obligately anaerobic bacteria were confirmed by 16S ribosomal DNA (rDNA) sequencing. Results indicate that the intestinal and bone-asso ciated samples contained the greatest diversity of bacterial taxa and that members of the family Enterobacteriaceae represented 41% of all i solates and were predominant in the intestinal masses and sediments in proximity to the skeleton but were uncommon in the background sedimen ts. Enterobacter cloacae was the most commonly identified isolate, and partial rDNA sequencing revealed that Rahnella aquatilis was the corr ect identity of strains suggested by FAME profiles to be Yersinia ente rocolitica. No Bacteroides spp. or expected intestinal anaerobes were recovered, The only obligate anaerobes recovered were clostridia, and these were not recovered from the small intestinal masses. Microbiolog ical evidence from this study supports other, macrobotanical data indi cating the intestinal origin of these masses. Whether these organisms are direct descendants of the original intestinal microbiota, however, cannot be established.