Science AMA Series: I’m Jeffrey Marlow, a science journalist and postdoctoral scholar in geobiology at Harvard University, where I study exotic microbial metabolisms in an attempt to understand life's adaptations to extreme environments on Earth and beyond. AMA!


Hey Reddit,

Last month, I published a story for Undark Magazine ( on a remarkable team of virus hunters in the Democratic Republic of Congo. The premise of the story: if scientists can detail the places where lethal viruses simmer in wait, they can head-off a swelling pandemic and better manage outbreaks while they are still small and local. But finding out where known viral threats lurk and determining which new viruses are dangerous is a task with steep odds of success.

I’ll be here from 1pm-2:30 pm EST to answer questions about the limits of life and how scientists around the world are trying to get ahead of the next pandemic. Looking forward to hearing from you!

What environment is cataloged as an "extreme environment"?


Well that's an important question - and a good chance to offer a caveat that pertains to a lot of the questions I'll be answering. "Extreme" and "extremophile" are generally defined from an anthropocentric perspective - environments that would be extreme for we humans. So while an acid lake seems like a terrifying environment for us, to the microbes living there, it's a home to which they are suitably adapted. This office I'm sitting in now would be "extreme" to that species...

It's a relative term to be sure, but some of the most commonly studied "extreme" environments include places with high or low temperatures, high acidity or alkalinity, high pressure, extreme doses of radiation, or lack of water. To me, one potentially universal case of "extreme" biology is one where you're limited by net energy gain - check out this article for more:

What is the strangest place you know there is life?


The fact that there are cells living beneath the surface of the Earth - the so-called "intraterrestrials" - always gets me. They often grow very slowly, but it's enough to persist and occasionally reproduce. The current depth record is 2.5 kilometers underneath the bottom of the Pacific Ocean off of Japan!

What about old, dormant viruses our immune systems are no longer used to reemerging from melting permafrost as reported here?

Are these comparable threats to new viruses? Is there a difference in how scientists and public health professionals should try to prepare for them?


Part of what makes a pathogenic virus dangerous is the lack of preparation our immune system has had to develop biochemical defenses. This is why "spillover" events in which a pathogen jumps from an animal reservoir into humans are particularly scary - we don't really know what's hit us.

So yes, in that way, dormant viruses could be comparable to the billions of viruses swirling around the natural world that we have yet to encounter - in both cases, our physiology isn't prepared. That could be a problem, or - much more likely - it could be inconsequential, as the vast majority of viruses are benign.

Soon, however, scientists working on pathogens could have a better idea of the danger these kinds of permafrost-entombed viruses could pose. Right now, knowing a virus's genetic sequence doesn't get you too far in determining its threat level, but as biochemical models and our understanding of the human immune system improve, things could get a little more predictive...

What is the best way to get one's foot in the door for science journalism?

Additionally, would it make a massive difference if the individual had an MS vs a PhD?


There are a number of different paths into science journalism, but I'd recommend starting off by writing what you know. Whether it's a first-person account of an experience that only you have had, or an insightful look at a new research finding in your area of expertise, those kinds of subjects help you answer an editor's first question: why are you the one to write about this topic? With a good subject in hand, write a few practice pieces and get input from your friends and colleagues, and then make the pitch to editors when you think it's ready.

Another bonus: scientists are almost universally excited to talk about their work, so don't be shy about knocking on researchers' doors!

I'm a post grad student in biology and geology in France since two years. I'd love to work in field that associate the two discipline. I've learn about Archee and I found them to be quite impressive. I would love to hear your thoughts about exobiology and the study of form of life beyond earth. I feel like it might be an awesome field and since you're working in microbiology I hope you might be able to explain where's science right now on this question and could it be a field of tomorrow or do you think it seems like a dead end ? Thank you for your time


Well I certainly hope it's not a dead end! :) And given the incredible rate of discovery of new organisms - from soil to animal guts to kilometers beneath the surface of the Earth - there is a lot more to learn about how microbes operate and impact our planet.

To be a bit more specific, I think there are two things to be really excited about. On the exobiology front, instruments being sent to Mars and other celestial bodies are getting more and more sensitive - one instrument on NASA's upcoming Mars 2020 rover can detect a single cell in Earth-based experiments, so the needle in the haystack is getting more accessible. A newly planned mission to Europa and improved resolution of extrasolar planets are also compelling opportunities to make big discoveries. (One intriguing debate in this realm is whether hypothetical extraterrestrial life would first be found by "direct contact" - through a rover on a planet or moon in our own solar system - or by "remote sensing" of extrasolar planets' atmospheres. The instruments being developed in support of each effort are improving at an impressive rate.)

The other aspect is seeing what the study of "extreme" life forms - and microbial communities more generally - can teach us about all kinds of applications, from human health to alternative energy. We're learning that the default mode of life on this planet is through interacting communities, and previous efforts to put microbes to work for us have largely been neglecting this reality. As we develop more transferable lessons about how different organisms interact, we can tune organisms to produce an antibiotic on demand, for example, or turn greenhouse gases into biofuel. Learning from natural microbial communities is the critical first step.

With all the research that has been done on extremophiles so far: 1) What are some of the applications of the research gained from extremophiles we see in our day to day lives? 2) Besides the obvious 'finding life on other planets' application of such research, what else can we expect as a potential outcome from doing research on extremophiles?

Thanks for doing this AMA! Looking forward to reading your answers :)


The most industrially-relevant results from extremophile research are probably "extremozymes" - which are, you guessed it, enzymes made by extremophiles. These molecules are helpful because they can either perform new, exotic biochemical reactions, or they can operate under distinct conditions. For example, "taq polymerase" is a DNA-building enzyme isolated from microbes living in hot springs - it's the workhorse of DNA replication experiments in many labs (I'm eagerly awaiting a PCR reaction to finish at the moment...) and is a critical aspect of the DNA sequencing experimental pipeline.

Other extremozymes have found use in detergents or food processing plants, and many biotech companies are scouring the planet for useful additions to the arsenal...

Thanks for the AMA

With the Grand Finale of Saturn's Cassini mission currently underway, what have we done or what can we do to keep earth-bound microbes from infecting other planets or celestial bodies? Is there a standard procedure for sterilization, and how effective is it?


The avoidance of cross contamination is a major requirement for any NASA mission headed to another celestial body. The Office of Planetary Protection ( sterilizes all spacecraft to a very very low microbial load (check out their website to track down the exact acceptable concentration). They also have maybe the best motto of any workplace: "All of the Planets, All of the Time". Beat that!

The avoidance of contamination is a good application of the precautionary principle and proper scientific practice (if you unknowingly seed Mars with terrestrial microbes and later "discover" cells, it might not be possible to determine their provenance). However, it does mean that certain compelling regions of Mars - which could have temporary expressions of liquid water on the surface - are off limits, and once people land on Mars, a sterile exploratory presence is no longer an option.

Which body in our solar system do you think has the highest chance of
a) being able to support life, without any atmospheric or biologic engineering, as we know or predict it, and
b) possibly having extant life?

Do you think it is possible absolutely no life exists or has existed on any object in our own solar system (other than the Earth, of course)


You mean I have to pick a favorite?! It's a tough question, because it's human nature to fill in our knowledge gaps with wishful thinking. For example, we know a lot more about modern day Mars than, say, Enceladus, which means we haven't really gotten to the unsavory aspects yet - we're in the honeymoon (pun intended :) phase of outer Solar System exploration. So while there are very exciting hints of energy sources that could feed metabolisms (, there are many more lines of the checklist to go through - lines that we've already started to understand on Mars.

Short answer: Mars certainly seems to have had all the ingredients - but the key missing variable is time. Were the raw materials, liquid water, and sufficient energy available at the same place for long enough to develop or sustain life?

What environment on earth is the least hospitable for life? How do some microbes adapt to living in extreme environments, while others cannot?


There are very few uninhabited places on Earth - microbes are amazingly adaptable at finding food to eat and fuel to burn (anything from sulfide gas to uranium). But liquid water can occasionally be a limiting factor, and scientists working in Chile's Atacama Desert reported a while back that they'd found the "dry limit of life" (

A related and very interesting question is whether there are any "uninhabited habitats" on Earth - are there any places life could survive but doesn't inhabit? Based on the transport of water and air, it would seem that living cells could gain a foothold, but perhaps we just haven't found the right spot yet.

Hi Jeffrey,

Thank you for answering our questions. Are hyperthermophie that live in Yellow Stone National park able to adapt to extremely cold environments? How does a non acidic environment effect the hyperthermophies ability to live?


Probably not, as the specific adaptations that allow a cell to live in one extreme environment don't necessarily make it well suited for a different setting. For example, hyperthermophiles generally have proteins with dense, hydrophobic cores - this means they're tightly folded and less susceptible to the general disorder that reigns at higher temperatures, where molecular vibrations are enhanced and most proteins sprawl into worthless goo (or are "denatured" if we're being more technical about it). Cold-tolerant (psychrophilic) proteins are kind of the opposite - they're usually more flexible, so that they can perform biochemical reactions and change shapes even at low temperatures as molecular movements get more sluggish.

Some adaptations, however, do help in multiple types of extreme environments. Deinococcus radiodurans is a master at DNA repair - this is perhaps most helpful in high-radiation environments, but it's a transferable skill for any condition that breaks up genetic material (e.g., high temperatures or certain chemicals).

Do you think that "extreme" environments on earth where microorganisms can thrive can mimic the surface of other planets (like Mars)? If so, what does this mean for the field of astrobiology and, more importantly, for the discovery of life on other planets?


Yes, the global pursuit of "Mars analog" environments has a long history, but I think it's important to keep your specific scientific questions in mind. For example, if you're after a soil that mimics the physical properties of Mars to test spacesuits or rover wheels, then something like Mauna Loa, Hawaii might be your best option. Astrobiologically, a chemical analog might be different from an energetic analog. And of course Mars is not a homogenous place through all of space and time: where and when on Mars are you hoping to simulate? With all of those caveats, there are certainly some places that match up pretty well with Mars, like acid saline lakes, or serpentinization sites. But given the pervasiveness and interconnectedness of Earth's biosphere, it's dangerous to directly transfer biological potential between planets - rather, analog sites help show what types of metabolisms could have been possible, or what types of traces (isotopic or physical) such life could have left behind.

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