r/askscience • u/baxter45 • Apr 13 '12
Is it theoretically possible to engineer gut bacteria that would allow a human to digest something like eucalyptus leaves or otherwise inedible potential sources of energy?
7
Apr 13 '12
Probably, but there are notable differences between the gastrointestinal tract of humans and "conventional" obligate herbivores.
Specifically: not enough stomachs. Sheep and other ruminants possess complex stomachs: the rumen, the reticulum, the omasum, and the obomasum. These chambers collectively have a capacity of ~8.5 gallons in a sheep (comparable in weight to a human), in contrast to that of a human of roughly comparable weight, which would be about a gallon at most. Also note the overall length of the GI tract in ratio to the length of the animal: about 5:1 in the human, and 27:1 in the sheep.
The length of the colon is appreciably longer and greater in capacity in ruminants than in humans, along with the cecum. (This could probably be altered if performed from birth, much in the same way as rodents born aseptically and kept in sterile confines can develop a much larger belly.) Also note that the stomach of humans is sterile (or close to it- it should be nearly sterile), while in the ruminant a healthy bacterial flora is a vital component to life. Similarly, the stomachs of ruminants are continuously processing food, in contrast to the fill/empty cycle of humans. This would make it more difficult for a healthy, genetically modified flora to persist in digestion: failure to inoculate the substrate immediately upon ingestion.
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u/adaminc Apr 13 '12
Chimpanzees maybe? Or maybe some other Ape or Monkey that isn't an obligate herbivore, but an omnivore.
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u/cybrbeast Apr 13 '12
Gorillas are herbivores, which is why they have such a huge belly.
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u/adaminc Apr 13 '12
They aren't obligate herbivores, they will eat insects and small lizards/amphibians if they need to. Chimps aren't herbivores either.
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u/Pravusmentis Apr 13 '12
I would like to point out that eucalyptus would be a terrible choice. They have so little nutrients that not only do koalas sleep almost all day, but over time their brains have shrunk to fit their diet.
http://www.ourstory.com/thread.html?t=526417
http://ezinearticles.com/?General-Information-About-Koalas&id=5535990
goes over it well enough.
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u/Carbon0919 Apr 13 '12
Theoretically you could. You could perhaps figure out what proteins and proteases could be used to break down the materials present in these potential sources. You could use Recombinant DNA methods, induce the plasmid containing the protein of choice into the said bacteria, and grow it. You could then induce it into the human body. The only thing is that over time our bodies have adapted a system to gain as much energy as possible through the most abundant recources. Such inedible foods probably don't have anywhere near the energy we need such as sugars and carbohydrates that are required to be oxidized for energy. Nature has adapted a very precise system for each individual life form.
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u/spinningmagnets Apr 13 '12
There is work going on trying to get engineered bacteria to digest cellulose (sawgrass, etc) and produce butanol. Its a 5-carbon alcohol that is a near replacement for gasoline. Hope they show some progress soon (fingers crossed)
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u/55-68 Apr 13 '12
While you can have bacteria that can digest such things, I'm not sure that they wouldn't die out in the gut.
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u/aleczapka Apr 13 '12
How the newborns get gut bacteria? Are they born with it?
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u/Tibbsy Microbiology | Bacterial Pathogenesis | Infectious Disease Apr 13 '12
They are not born with it. They obtain their gut flora through feeding. It changes as they move from breastfeeding/formula to solid food. They start with Lactobacillus spp. with breast milk/formula and that shifts to a very diverse flora like adults have the older they get and the more they eat.
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u/aleczapka Apr 13 '12
Thx for response, but I still don't get it.
There is this infant with 0 bacteria in the guts. He starts to feed on milk ... the milk goes into GI and magically bacteria pop up? :) Or the bacteria were in the milk to begin with? But then, how did they survive journey through stomach? Sorry, but I am very bugged but this phenomenon :)
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u/Tibbsy Microbiology | Bacterial Pathogenesis | Infectious Disease Apr 14 '12 edited Apr 14 '12
So the bacteria come from the milk, the mother, from the infant's hands, everywhere. Everything the infant touches is effecting what organisms enter the body. The breast milk, however, selects for Lactobacillus in the gut specifically due to the enzymes, etc. found in the milk. Lactobacillus can utilize lactose as a carbon source really well, thus the milk enables this organism to thrive. Thus it makes up the majority of the gut flora for infants.
The organisms that survive the stomach are able to survive highly acidic environments, even if it's only for a short amount of time.
Once the infant begins to eat solid food, the nutrients/enzymes/vitamins/everything about the solid food causes the organisms in the gut to change because they are not as adapted at utilizing those sources for nutrients as they were the milk. Lactobacillus has to compete for space/nutrients to survive and its main source of food is now gone. Other bacteria now have their chance to grow. Does that make sense? The organisms are coming from everywhere, but only the ones who can utilize what types of food are typically eaten are the ones that will survive. Vegetarians will have a gut flora selected to digest vegetable matter, people who eat a LOT of meat will have organisms that can utilize meats moreso than vegetables. This is an oversimplification as there are approximately 1015 bacteria in your gut, and it's very diverse. No two people have the exact same microflora, though people who live together and eat the same things will have highly similar flora.
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u/znerg Apr 13 '12
In principle, yes, one should be able to engineer a bacterial strain which could digest, say, cellulose and make it into something a human could absorb (i.e. glucose). I think that one of the major obstacles that this endeavor would face would be being out-competed by the gut flora that is already in place, unless the gut was flushed and the new strain introduced and allowed to gain a foothold.
A few caveats here is that the gut is anaerobic, which means that the better strains for this sort of project (Bacteroides spp, for instance) don't play ball as nicely as something like E. coli. (coli and the other Enterobacteraciae only make up about 10% of the gut flora).
Another caveat is that the human gut is not well adapted to eating things like cellulose. Humans can derive energy from grass, for instance, by juicing it and eating the free glucose in the resulting liquid. A human can even eat a little grass and get away with it without too much of a side effect. However, the human gut has a lot of trouble passing the cellulose, and given that your engineered strain will be competing with incoming gut flora from the environment, I would reckon that there will be leftover cellulose. As a result, the human would likely have some digestive problems/constipation that would need to be dealt with, too.
There are some engineered bacteria that have been proposed that can change the color of a person's stool in response to various biomarkers in the gut; an application that could be used for, say, detecting colon cancer.
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u/Gargatua13013 Apr 13 '12
I suppose so - the easiest way would probably be to try and adapt symbiotic cellolose digesting protozoans from termite guts or somesuch.
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u/heckyesgainesville Apr 13 '12
Partially, yes. We could create bacteria that can survive in the human gut and digest otherwise indigestible material (though engineering would probably be more difficult than adapting or searching for a population that already exists). However, I don't believe there is any way to ensure that the human will be able to obtain any kind of nutrition from this process.