Petabase-scale Data Mining Identifies Novel Clostridial Species and Neurotoxins Associated with Ancient Human DNA

Abstract

Analyzing microbial genomes found in archaeological samples can provide insights into the origins of modern infectious diseases. A large-scale metagenomic analysis of archeological samples discovered bacterial species related to modern-day Clostridium tetani (which produces the tetanus neurotoxin (TeNT) and causes the disease tetanus). Draft genomes were assembled from 38 distinct human archeological samples (which came from five continents with the oldest sample estimated to be ~6000 years old) and which displayed hallmarks of ancient DNA damage to varying degrees. A phylogenetic analysis of the draft genomes found several which fall into existing C. tetani clades, several potentially novel C. tetani lineages, and a potentially novel Clostridium species related to modern C. tetani. Fifteen TeNT variants were found, including a unique variant found exclusively in ancient samples from South America. A TeNT variant associated with a ~6,000-year-old Chilean mummy sample was experimentally tested and was found to induce tetanus like muscle paralysis in mice with a potency similar to modern TeNT. This work provides the first identification of neurotoxigenic C. tetani in ancient DNA, the discovery of a potentially new Clostridium species, and the discovery of a tetanus like neurotoxin which is functionally active and able to cause disease in mice.