Getting High On Life

Biology concepts – bacteria, climate, respiratory, birds, arthropods, astrobiology, clouds

Carl Sagan wasn’t just the host of the original Cosmos on TV.

He solved the riddles of Venus’ high temperature, the seasons

on Mars, and the color of Titan. He also wrote one of my

favorite speculative fiction novels, Contact. The movie is

good; the book is better.

The astrophysicist Carl Sagan said, “There are naive questions, tedious questions, ill-phrased questions, questions put after inadequate self-criticism. But every question is a cry to understand the world. There is no such thing as a dumb question.” A cry to understand the world – so keep asking the questions, even if they seem silly.

Today’s question might seem a little naive – Is there any life that could escape Earth? But I assure you, there’s more to it than you might think – and no, the answer isn’t an astronaut. Let’s put it another way - is there any living organism that could get high enough on its own to leave our atmosphere?

Well, I guess the first prerequisite for escaping our atmosphere would be an organism that could get really, really high. Some birds can fly at absurd altitudes.

The Ruppell’s Griffon Vulture (Gyps rueppellii) has the highest recorded flight. On November 29, 1975, a Ruppell’s vulture was sucked into the jet engine of a plane flying at 39,700 ft (12.1 km, Mt. Everest is 9.0 km) over the Ivory Coast in Africa. A unfortunate flight plan for the bird, but amazingly the plane landed safely after ingesting a bird with a 10-foot wingspan.

These two pictures are not at the same scale. The Ruppell’s

vulture on the left has a wing span of about 10 ft (3 m),

while the bar headed goose on the right (see the bars?) has

a span of about half that. They should not box one another,

it’s be a slaughter. But still, these are both much bigger than

most birds. Is their longer wing span part of their success at

high altitudes? Songbirds rarely fly above 2000 feet.

We don’t know how often the vultures venture that high, but the bar headed goose (Anser indicus) makes a habit of flying over Mt. Everest. This is a migratory bird that flies over the Himalayas twice a year, sustaining 8-hr flights at more than 28,000-29,000+ feet (8.8 km).

The real question is why birds would fly so high. As you ascend, the air becomes thinner; fewer molecules make the atmosphere less dense. Since bird flight is basically supported by the air, thinner air makes flying much more difficult.

Difficult flying means that more energy is required. Birds live right on the edge of oxygen debt all the time; flying is tough at any altitude. But high in the air, it becomes even harder and requires more energy. And what’s needed to make energy in the form of ATP – oxygen (see this post) – the very thing there is less of at high altitude.

The bar headed goose and his compatriot avians breaks some rules in order to become a high flier. Birds in general are better at oxygenating their muscles, because they can exchange oxygen for carbon dioxide on both their inhalation and their exhalation (this will be the focus of s series soon). But that isn’t all.

Birds can also pant better than mammals. Panting is way to get more oxygen to the muscles, but it comes at a cost - it brings blood vessel constriction in the brain (an attempt to prevent oxidative damage). This makes for poor control, focus and decision making. But birds can pant much longer and harder without constricting brain vessels, so they don’t make stupid decisions - birds aren't bird brained.

Bar headed geese go even further (a 2013 study). The blood vessels in their muscles penetrate deeper and are more extensive. This can supercharge their muscles with oxygen so they can make more ATP and flap more energetically. Finally, the hemoglobin (oxygen-carrying molecule) of bar headed goose red blood cells is slightly different than that of other birds. It grabs onto oxygen molecules easier and quicker, so it does a better job of transporting the maximum amount of oxygen to the muscles.

We humans may not want to flap at high altitudes, but we could learn a lot from the bar headed goose about maximizing oxygen utilization. That’s where we get most of our best ideas – we steal them from nature’s rule breakers.

Many species of spiders, mites, and small caterpillars use

kiting as a means of dispersal. Remember that these are

newborns, and are usually of the smaller species, so these

fellows are awfully small. That makes it possible for a breeze

to catch the silk they spin straight up into the air and carry

them off to new neighborhoods. This is thought to be one of

the primary ways arthropods colonize newly formed islands.

But we shouldn’t restrict our discussion to birds, there may be other things that get high (pun intended). The winds can help out. Some small arthropods disperse themselves as youngsters by ballooning with silk. Spiderlings (newly hatched spiders) risk being eaten by siblings if they hang around after hatching, and too many spiders in one area makes it hard to find food, so they get as high as they can and then shoot out a strand of silk.

The wind picks up the youngsters and deposits them somewhere else. However, the wind sometimes doesn’t want to let them go. They've been know to travel into the jet stream, and have been noted living in weather balloons at more than 16,000 ft (4.9 km).

Bees too have been found on the slopes of Mt. Everest (5.6 km). A 2014 study says bees could theoretically fly at almost 30,000 ft.; they could look down at Mt. Everest if they chose to. The researchers reduced the density of air and the oxygen concentration to match what would be found on top of the world and the bees flew just fine. They compensated not by beating their wings faster, but by widening and lengthening their stroke. Pretty good for an organism that many mistakenly believe shouldn’t be able to fly at all. But just because they could fly at that altitude, doesn’t mean that they do.

For one thing, bees and other arthropods go dormant when temperatures dip into the 40’s ˚F (7-10˚C) they become immobile and if they stay that way, they die. Not a good candidate for escaping Earth, where the temperature approaches -40˚C as you travel through the clouds.

These are the major types of clouds and their average altitudes.

They carry dust, water, chemicals, and apparently a whole lot of

bacteria and fungi. The 2013 paper says the bacteria act as seeds

for cloud formation and can therefore affect the weather.

Powerful beings.

The clouds are up there, could they harbor life? They contain water; life needs water. There are several types of clouds and they sit at various altitudes based on type, topping out at about 13 km (8 mi). The highest clouds are at about the same altitude that the griffon vulture has been known to fly (see picture).

Do all clouds have a living lining? You betcha. A 2013 study has shown that the clouds are actually their own biological environment. Bacteria, some from the ground, some from the ocean, and perhaps some from the air, are living and dividing up in the clouds. The study sampled air at 10,000 feet and found that air over water, had more marine organisms, while air over land had more soil organisms. They also found that hurricane air had many more organisms, so they hypothesize that strong winds pull up more organisms into the upper atmosphere.

But wait you say, the vulture was at 39,000 feet, and these bacteria were only at 10,000 ft. Well, let’s go higher. A 2009 study from India showed that microbes were living as high as 25 miles (41 km) in the stratosphere. This shames the vulture and he makes him feel inadequate. What’s more, the 2009 study found three strains of bacteria in the clouds that are not found on the surface of the Earth!

Meteorites are one way that life might travel from planet to

planet. The organisms would have to survive the jolt that

speeds them to escape speed (bacteria can), and they have to

survive the temperatures of reentry. Interestingly, studies

show that even though the surface of a meteor entering the

atmosphere is several thousand degrees, it feels like a warm

summer day just a few centimeters deeper.

Bacteria are particularly well suited for life in the atmosphere. There are bacteria that can withstand intense radiation, can live in extreme cold temperatures, and can live nearly without water. These sound like good candidates for something that could escape Earth altogether.

A 2012 draft genome of one of these bacteria, Janibacter hoylei, confirms that it is different from any organism found previously on Earth. These bugs might be living their entire existences in the upper reaches of the atmosphere.

But we could look at this from the other direction as well. Could J. hoylei have come from space and is just living in the clouds because it liked the first place it saw when it got here? Astrobiologists are excited to study these high altitude bacteria in terms of whether they could seed other planets or whether life could come here from other places.

The hiccup in all our hypothetical space entering organisms is something called escape speed. In order to leave Earth’s gravitational pull, an object on the ground must travel at 11.2 km/sec. The escape speed decreases as you travel away from the center of mass, but even at 9000 km, an object must travel at 7.1 km/sec. A bullet fired from a rifle travels at about 1.7 km/sec, so you get the idea. It ain’t easy to leave Earth behind, even if you happen to be rugged enough to survive space (as some bacteria and lichens can, see this post and this post).

The Earth’s magnetic field protects life on the planet from many

types of deadly radiation. Near the poles, the earth’s magnetic field

lines bend to pass through the center of the planet. It is here at the

poles that the radiation can interact with the field lines in a position

for us to see. These are the Northern and Southern Lights.

One theory holds that bacteria living in the high atmosphere could be affected by the magnetic field lines of the Earth and sort of ride along a magnetic railway. Tom Dehel, an electrical engineer for the FAA, proposed in 2006 that electromagnetic fluxes, like the solar flares and fields that produce the auroras in the northern and southern hemispheres, could provide charged bacteria with enough energy that they could escape Earth’s gravitational pull. Not one scientist I could find has signed on to this idea. But still, there are no silly hypotheses, they’re all just a cry for the truth.

Next week, another question with a more fascinating answer than you would expect - why is it so hard to catch or swat a fly?

Pawar SP, Dhotre DP, Shetty SA, Chowdhury SP, Chaudhari BL, & Shouche YS (2012). Genome sequence of Janibacter hoylei MTCC8307, isolated from the stratospheric air. Journal of bacteriology, 194 (23), 6629-30 PMID: 23144385
 

Dillon ME, & Dudley R (2014). Surpassing Mt. Everest: extreme flight performance of alpine bumble-bees. Biology letters, 10 (2) PMID: 24501268

Hawkes LA, Balachandran S, Batbayar N, Butler PJ, Chua B, Douglas DC, Frappell PB, Hou Y, Milsom WK, Newman SH, Prosser DJ, Sathiyaselvam P, Scott GR, Takekawa JY, Natsagdorj T, Wikelski M, Witt MJ, Yan B, & Bishop CM (2013). The paradox of extreme high-altitude migration in bar-headed geese Anser indicus. Proceedings. Biological sciences / The Royal Society, 280 (1750) PMID: 23118436

Does Life Come In XXXS?

Biology concepts – characteristics of life, archaea, bacteria, mycoplasma, synthetic biology, symbiosis, parasitism, nanobacteria, genome

As part of this blog, we have talked about some pretty small life. Wolffia globosa is the smallest flowering plant, only 0.6 mm long. We also talked about archaea, a different kingdom than bacteria, but still on the smallish side of life. The tardigrade is the toughest animal, but is also one of the smallest, at 100 µm (0.00394 inch).

The organism on the top is T. dieteri, and arthropod, just

as is any crab or spider. The size is deceiving. The pictures

on the bottom are to scale and are copepods, also

arthropods. The organism on the top is a parasite of the

organisms on the bottom. The small blue line? That would

be the scaled size of T. dieteri. So…. it’s SMALL.

The question for today is – is there a minimum size for life? Candidates might include bacteria or archaea; heck there’s an arthropod, Tantulacus dieteri, that's only 85 µm long! As long as we can keep finding smaller and smaller cells, we know that the minimum size for life is that small or smaller. So we keep looking – you’d be surprised how important it is to keep looking for smaller life.

Here’s one thing we should be able to agree on, viruses don’t get to play in our game. Viruses are very small, but they're not life! We’ve talked about this before - the seven characteristics of life (see this post). Viruses need a host in order to replicate, they don’t manage homeostasis, and they aren’t cells, so they aren’t life.

So how small has actual life become? Let’s assume that since tardigrades and T. dieteri are over 50 µm, huge when compared to some bacteria, our current minimum for life is probably a bacterium or archaea.

Let’s go straight to the genus of smallest bacteria we know about – the mycoplasma (from mykes = fungus, and plasma = formed). They were first described in 1898, but the observer didn’t have a clue what he was looking at; hence the fungal part of the name.

Mycoplasma don’t have the traditional cell wall of many bacteria, so they look different and this might be why they were mistaken for fungi. Whatever the scientists thought of them, they were confusing enough to be roundly ignored for 50 years. Rediscovered in the 1950’s-1960’s, this time they were thought to be L-forms of bacteria. L-forms are organisms that for some reason have lost their cell wall.

There are stable forms of L-bacteria; they can live divide and live on without their cell wall. There are also unstable L-forms as well; those that may revert to walled bacteria at any moment. Are mycoplasma simply bacteria that have lost a cell wall? Nope. They didn’t have a cell wall to lose. They have no cell wall genes, so if they had a cell wall, it was millions of years ago, before they became their own genus.

The difference between some free living cells. You can

probably see the E. coli in bright green, but you may have

to squint to see the mycoplasma above it. It’s pink. Really,

it’s there. Compare these sizes to those of the arthropods

above. 1 mm is equal to 1000 µm.

Mycoplasma is really, really, SMALLLLLLL.

Mycoplasma are generally described in the range of 0.2-0.8 µm in diameter. But this is a little misleading, because they are often not spherical. Even without a cell wall, they can take interesting three-dimensional forms and maintain them. Mycoplasma pneumoniae, which causes a form of …..….. anyone?…….. right, pneumonia, is pear shaped, so its 0.25 µm diameter is actually the measurement on its short side.

So mycoplasma are small, but they still have to play by the rules. They contain DNA and salts and proteins and ribosomes and other things that take up room. A single ribosome is about 50 nm in diameter (0.05 µm or 0.00000005 m), so there must be a certain volume required for the cell to function – a minimum size for life.

Which of the mycoplasma species is the smallest? Mycoplasma genitalium is considered to be the smallest mycoplasma known, and the smallest form of free-living organism - my gosh – you can fit about 400 M. pneumoniae inside one E. coli! As such, it is the current minimum size for life that we have. M. genitalium is 200 nm (0.2 µm) x 600 nm (0.6 µm), so they’re pretty dawg on small. Let’s put it this way, there are 25,400,000 nm in one inch – mucho small.

It is important to note that M. genitalium is free living, but does need some help. It uses cholesterol in its membrane but doesn’t make it itself. It picks it up from the cells that it lives near……wait for it….. your genital epithelium.

One of the human diseases that is becoming more

convincingly associated with M. genitalium is pelvic

inflammatory disease (PID). Resulting when many

different sexually transmitted diseases go untreated,

PID can cause permanent damage to the reproductive

organs of women. It is important to get treatment early.

The inflammation of PID may be associated with the

fallopian tubes or ovary, and will cause a chronic pain

in the lower abdomen, bleeding and pain on urination.

M. genitalium is a cause of non-gonococcal urethritis (inflammation of the urethra). A late 2013 review states that 1-3% of the general population is infected with M. genitalium, more than with gonorrhea. It is linked to pelvic inflammatory disease, and the review cites studies showing that people infected with this mycoplasma are more at risk for HIV and have more dual infections. It’s a sexually transmitted organism, just another reason for proper restraint. But even though it's helped out by your genital epithelium, it can live on its own and divide outside a host, so it's considered a free-living organism.

The idea of free-living is important because M. genitalium also has a very small genome (amount of DNA in one cell, including the list of all its genes). M. genitalium has about 580 kbp of DNA where kbp = kilobase pairs. Remember that DNA is doubled stranded (usually) so each base is paired with another. Knowing this, we count them as a unit. In all, M. genitalium has just 520 or so genes; it can make about that many proteins.

Genome size could be another way of determining the minimum size of life - what's the minimum number of genes or number of base pairs of DNA for an organism to still meet all seven characteristics of life? As of summer 2014, no organism smaller in size than M. genitalium has been described, but there have been some other organisms discovered with smaller genomes.

Nanoarchaeum equitans was thought to have the smallest gene for a while, with only 491 kbp of DNA. It is an archaea that lives on the edge of hydrothermal vents at the bottom of the ocean. But it is an obligate symbiont with another archaea; it can’t survive without its partner, so can you say it has the minimal genome? It relies on another organism’s DNA.

On the left is the leafhopper in which N. deltocepahlinicola makes

his home. Well inside its cells that is. The leafhopper survives on

phloem and xylem; high in carbs but little protein. The bacterium

makes the amino acids the leafhopper can’t in exchange for energy

in the form of ATP. On the right is a colored photomicrograph of

the abdomen. The red is one type of endosymbiont bacteria,

the green is N. deltocephalinicola.

This is also true of Carsonella ruddii (159 kbp, 182 genes) and Nasuia deltocephalinicola. They are bacteria that must live inside insect cells, like those of grasshoppers. N. deltocephalinicola has the smallest known genome (112 kbp, 137 genes), but it doesn’t even make ATP, it steals it from the arthropod cells. This could hardly be considered free living, and so it can’t be considered the minimal genome for life. And even at that, their cell sizes are still bigger than M. genitalium.

So why is it important to find the minimal size and minimal genome for life? So we can use the information. J. Craig Venter (of the human genome project) wanted to develop a synthetic form of life (synthetic biology); a bacterium that could be developed to provide hydrogen for energy or eat waste to reduce pollution. Others say we need to know so that we can better recognize life on other planets, or life that may have come here from other planets (astrobiology).

Being J. Craig Venter, develop a synthetic form of life is exactly what he and his research institute did. It’s interesting that Venter was one of the scientists that first sequenced the entire M. genitalium genome in 1995. Some 15 years later, Venter’s JCVI-syn1.0 (2010) was the first synthetic life, housing 1000 kbp and 500 or so genes. The genome was based on that of another mycoplasma, M. mycoides. They modified the genome, and introduced it into a cell membrane that had been evacuated of all its constituents. The resulting cell was capable of growing, dividing, you know…. living.

If M. genitalium represents our current estimate for the minimum size of life, it’s only because we’re thinking of life as we know it. Perhaps we have already found life that is smaller, and the minimum size is actually much smaller than M. genitalium.

This is a photomicrograph of a meteorite from Mars. The

small spheres (like the ones the arrows point to, are

supposedly nanobacteria. Proof of life on Mars,

contamination from Earth nanobacteria, or just mineral

spheres that look a little like incredibly tiny bacteria?

The answer is C.

Something termed a nanobe and something else called a nanobacterium were described 20-30 years ago. Nanobes were first found in the rocks that came up during oil drilling in Australia, while nanobacteria were also found in surface rocks.  The size of both (about 1/20 size of M. genitalium) negates their use of ribosomes and DNA. They stain for DNA, but this may be artifact, the artificial result of other things picking up the stain.

But nanobes/nanobacteria have their proponents. Some scientists say that since no DNA has been exhibited, they are a completely different form of life, so size restriction (big enough to hold ribosomes) doesn’t apply. Nanobacteria are also claimed to be important in human disease, as these structures are found in many calcifications of diseased tissues.

On the other hand, nanobacteria are probably just mineral formations. A 2013 study showed that they form spontaneously from many different biological fluid samples, and their appearance in diseased tissues is more a sign of disease than a cause of it. We’ll just have to keep looking for something smaller.

Next week, another question tackled and dissected - think pink.

Manhart LE (2013). Mycoplasma genitalium: An emergent sexually transmitted disease? Infectious disease clinics of North America, 27 (4), 779-92 PMID: 24275270

Wu CY, Young L, Young D, Martel J, & Young JD (2013). Bions: a family of biomimetic mineralo-organic complexes derived from biological fluids. PloS one, 8 (9) PMID: 24086546

Gibson DG, Glass JI, Lartigue C, Noskov VN, Chuang RY, Algire MA, Benders GA, Montague MG, Ma L, Moodie MM, Merryman C, Vashee S, Krishnakumar R, Assad-Garcia N, Andrews-Pfannkoch C, Denisova EA, Young L, Qi ZQ, Segall-Shapiro TH, Calvey CH, Parmar PP, Hutchison CA 3rd, Smith HO, & Venter JC (2010). Creation of a bacterial cell controlled by a chemically synthesized genome. Science (New York, N.Y.), 329 (5987), 52-6 PMID: 20488990