Comment by Den_VR
6 hours ago
> metabolic pathways that span multiple species are common to the point that trying to isolate a given species’ contribution can miss the effect entirely.
What does this mean?
6 hours ago
> metabolic pathways that span multiple species are common to the point that trying to isolate a given species’ contribution can miss the effect entirely.
What does this mean?
I think author is saying that you ingest compound A, microbe 1 eats A and secretes B, microbe 2 eats B and releases C. C happens to do <positive thing>. You could imagine parallel pathways where maybe microbe 2 only works if it is in the presence of microbe 3.
Meaning everything is a mess to try and disentangle.
So, a metabolic pathway is the set of steps by which an organism converts one molecule into another - this can be by splitting a molecule into pieces, by adding or removing an atom or small group of atoms, or by combining two different molecules into a larger or more complex one. By way of a very, very simple pathway, your body breaks down ethanol (alcohol, C2H5OH) by first removing a hydrogen (and causing the oxygen to double-bond to the carbon) to create Acetaldehyde, CH3CH=O, and then oxidizing that by swapping the H remaining on the second carbon for an OH to create Acetic Acid, the primary component in vinegar. So, when we say your body metabolizes ethanol into acetic acid, we're talking about a two step metabolic pathway.
Bacteria can stash intermediate pathway results outside of their cell wall for various reasons (sometimes the chemical environment is more amenable outside the cell than inside, sometimes buildup of the intermediates can disrupt other processes, sometimes that's just how it happens - biology is weird), and very often what you'll see is that a multi-step metabolic pathway can span across multiple different organisms - so, species 1 takes up a starting material, performs a handful of modifications, and then excrete the results outside the cell wall, and then another species will take up that substance and perform additional modifications on it, and this can run through several species before reaching the terminal state in the pathway (including the first species again). This works because each bacteria can have different enzymes and different internal chemistry which can affect how easy or likely a reaction is.
Nitrogen fixing is a notable example of this - it's not just one species in the roots of legumes responsible for taking N2 and converting it into ammonia, there's 6 or 7 that take part in that pathway.