Scientists Reconstruct Eight Genomes of 6500-Year-old Bacteria

Technology

March 31st, 5:56am

Cairo- Hazem Badr

Salmonella Typhimurium. (USIG/Getty Images)

The Neolithic revolution, and the corresponding transition to agricultural and pastoralist lifestyles, represents one of the greatest cultural shifts in human history, and it has long been hypothesized that this might have also provided the opportunity for the emergence of human-adapted diseases. A team of researchers from the Max Planck Institute for the Science of Human History studied human remains excavated across Western Eurasia and reconstructed eight ancient Salmonella genomes. Their study was published in the Nature Ecology & Evolution journal on February 4. The researchers used a technique called HOPS, a bacterial screening pipeline that helps separate and sequence DNA. It enabled them to screen thousands of archaeological samples for traces of Salmonella DNA. The researchers screened 2,739 ancient human remains in total, eventually reconstructing eight Salmonella genomes up to 6,500 years old -- the oldest reconstructed bacterial genomes to date. This highlights an inherent difficulty in the field of ancient pathogen research, as hundreds of human samples are often required to recover just a single microbial genome. The genomes in the current study were recovered by taking samples from the teeth of the deceased. The presence of Salmonella in the teeth of these ancient individuals suggests they were suffering from systemic disease at their time of death. The individuals whose remains were studied came from sites located from Russia to Switzerland, representing different cultural groups, from late hunter-gatherers to nomadic herders to early farmers. In a report published on the Max Planck Institute, co-author Alexander Herbig explained that "This broad spectrum in time, geography, and culture allowed us, for the first time, to apply molecular genetics to link the evolution of a pathogen to the development of a new human lifestyle." "With the introduction of domesticated animals, increased contact with both human and animal excrement, and a dramatic change in mobility, it has long been hypothesized that the transition to a sedentary, agricultural lifestyle enabled more constant and recurrent exposure to pathogens and thus the emergence of new diseases. However, prior to the current study, there was no direct molecular evidence," Herbig added. The ancient metagenomics provide an unprecedented window into the past of human diseases. The researchers now have molecular data to understand the emergence and spread of pathogens thousands of years ago. The researchers were able to determine that all six Salmonella genomes recovered from herders and farmers are progenitors to a strain that specifically infects humans but is rare today, Paratyphi C. Researchers had previously suggested that this strain of Salmonella spread from domesticated pigs to humans around 4000 years ago, but the discovery of progenitor strains in humans more than 5000 years ago suggests they might have spread from humans to pigs. "Managing to separate the Salmonella genomes from the human excrement represents an important development that would provide a better understanding of these bacteria known for their constant surprising developments," Dr. Khalid Moussa, professor of zoonotic diseases at the faculty of veterinary medicine, Assiut University, told Asharq Al-Awsat. "A few months ago, scientists discovered a gene called "mcr-9" in a sequence of the Salmonella genome. They found that this gene gives the bacteria resistance to Colistin, one of five antibiotics featured on the World Health Organization's List of Essential Medicines, which doctors resort to after trying all other infection control options," he added.

from Asharq AL-awsat https://aawsat.com/english/home/article/2208481/scientists-reconstruct-eight-genomes-6500-year-old-bacteria