How genome sequences tracked down an ancient disease

How genome sequences tracked down an ancient disease

Subject : Science and technology

Section: Biotechnology

Concept :

• The ‘Black Death’ causing bacteria’s prehistoric trail has been traced by scientists thanks to advanced gene-sequencing techniques.
• The ‘black death’, or the Great Plague, of the 14th century, was one of the deadliest epidemics in human history. It’s a clear example of the profound influence infectious disease outbreaks can have on society, economy, and culture.
• It was also probably one of the most impactful epidemics, considering it left an indelible mark on humankind and shaped the collective memory of many subsequent generations.

Whole Genome Sequencing

• All organisms have a unique genetic code, or genome, that is composed of nucleotide bases- Adenine (A), Thymine (T), Cytosine (C) and Guanine (G).
• The unique Deoxyribonucleic Acid (DNA) fingerprint, or pattern can be identified by knowing the sequence of the bases in an organism.
• Determining the order of bases is called sequencing.
• Whole genome sequencing is a laboratory procedure that determines the order of bases in the genome of an organism in one process.

Methodology:

• DNA Shearing:
  • Scientists begin by using molecular scissors to cut the DNA, which is composed of millions of bases (A’s, C’s, T’s and G’s), into pieces that are small enough for the sequencing machine to read.
• DNA Bar Coding:
  • Scientists add small pieces of DNA tags, or bar codes, to identify which piece of sheared DNA belongs to which bacteria.
  • This is similar to how a bar code identifies a product at a grocery store.
• DNA Sequencing:
  • The bar-coded DNA from multiple bacteria is combined and put in a DNA sequencer.
  • The sequencer identifies the A’s, C’s, T’s, and G’s, or bases, that make up each bacterial sequence.
  • The sequencer uses the bar code to keep track of which bases belong to which bacteria.
• Data Analysis:
  • Scientists use computer analysis tools to compare sequences from multiple bacteria and identify differences.
  • The number of differences can tell the scientists how closely related the bacteria are, and how likely it is that they are part of the same outbreak.
• Advantages:
  • Provides a high-resolution, base-by-base view of the genome
  • Captures both large and small variants that might be missed with targeted approaches
  • Identifies potential causative variants for further follow-up studies of gene expression and regulation mechanisms
  • Delivers large volumes of data in a short amount of time to support assembly of novel genomes
• Significance:
  • Genomic information has been instrumental in identifying inherited disorders, characterizing the mutations that drive cancer progression, and tracking disease outbreaks.
  • It is beneficial for sequencing agriculturally important livestock, plants, or disease-related microbes.

Black Death Disease

• The term Black Death refers to the bubonic plague that spread across Western Asia, Northern Africa, Middle East and Europe in 1346-53.
• Most scholars agree that the Black Death, which killed millions, was caused by bacterium Yersinia pestis and was spread by fleas that were carried by rodent hosts.
• The microorganism Y. pestis spread to human populations, who at some point transmitted it to others either through the vector of a human flea or directly through the respiratory system.
• Contemporaries who wrote about the epidemic, often described the buboes (hard, inflamed lymph nodes) as the distinguishing clinical feature.
• In the 14th century, the epidemic was referred to as the ‘great pestilence’ or ‘great death’, due to the demographic havoc that it caused.
• Due to a lack of comprehensive historical data from that time, it is difficult to know the exact death toll.