Zombie Genes, Slurpee Machines and Disease X


The story doesn’t always end after you kill a microbe. That death, in fact, can mark the beginning of a whole new life – for the organism’s genes.

According to MIT geneticist Eric Lander (below video), it works like this. Most bacteria carry, in addition to a regular set of chromosomes, an extra set of gene-carrying chromosomes called plasmids. And these genes often encode a protein that confers resistance to a range of antibiotics.

The reason for the presence of genes on plasmids is because plasmids are mobile, they move between living bacteria, conferring resistance along the way. But their movement isn’t confined to living bacteria: “It turns out that when bacteria die their cells crack open and their guts spill out – these little circles of DNA, these little plasmids.” At which point other bacteria will “slurp them up.”

Dr. Lander says this ability to slurp up zombie genes “is a little scary…. Because if we start using antibiotics willy-nilly, it’s pretty easy [to see] that if one species of bacteria had a … plasmid with a resistance gene, another species entirely can pick it up by horizontal transfer. [I]n fact, we are seeing an epidemic of antibiotic-resistant bacteria. Because as we use more antibiotics … [we’ve] selected for the bacteria that have picked up these things…. Not good, not good. And we’re seeing a huge spread of antibiotic resistance.“ (Emphasis added.)

This huge spread of drug-resistant microbes might be nearing critical mass. Last month, for example, the World Health Organization issued a list of disease-causing pathogens that have the potential to spread and kill worldwide and for which there are currently no, or insufficient, countermeasures available:

  • Crimean-Congo haemorrhagic fever (CCHF)
  • Ebola virus disease and Marburg virus disease
  • Lassa fever
  • Middle East respiratory syndrome coronavirus (MERS-CoV) and Severe Acute Respiratory Syndrome (SARS)
  • Nipah and henipaviral diseases
  • Rift Valley fever (RVF)
  • Zika
  • Disease X

The ominous sounding Disease X “represents the knowledge that a serious international epidemic could be caused by a pathogen currently unknown to cause human disease.” A “pathogen currently unknown” includes an existing microbe that, say, gains the ability to jump from animals to humans, for airborne transmission (imagine if HIV could do that), or mutates to become more virulent or more resistant to our drugs.

Experts in the field such as Dr. Michael Osterholm, founding director of the Infectious Disease Center for Research & Policy at the University of Minnesota, have been predicting a serious international epidemic, saying it’s not a question of if, but when. In his book Deadliest Enemy: Our War Against Killer Germs, Osterholm narrows the threat to antibiotic-resistant bacteria and the influenza virus, whose pathogenic potential relies in good part on their ability to mutate rapidly:

[T]here are only two microbial threats that … fit this description for pandemic potential. One is antimicrobial resistance and the very real threat of moving ever closer to a post-antibiotic era … a world more like that of our great-grandparents where deaths due to infectious diseases we now consider treatable are once again commonplace. The other is influenza, the one respiratory-transmitted infection that can spread around the world in short order and strike with lethal force.


One way microbes mutate rapidly is by the aforementioned plasma-mediated horizontal gene transfer. Here’s the engaging Eric Lander, former co-chair of President Obama’s Task Force on Combating Antibiotic-Resistant Bacteria, explaining to his first year MIT biology students how zombie genes and slurpee machines combine to yield Disease X potential. (The relevant bit runs from 2:40 – Why do cells have plasmids? – to 7:10.)


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