I haven't heard of the Impossible Burger until you wrote it. The FDA won't approve it yet from what I am reading.
Just the one ingredient that gives it the authentic beef taste. Soy Leghemoglobin - which is a component of soy plant's roots and is apparently mass produced through a process involving yeast for use in the burger.
The FDA has just recently not given approval on the basis that soybean plant's roots have never been part of human's diet. While I agree it's not a normal menu item in any culture I'm aware of - I do doubt it's never been tried, and it is natural in the sense that the ingredient itself is natural - but this may be the first time it has been mass produced for a more concentrated amount in vegan foods (in this case a vegan burger) using yeast.
Given it's history with Aspartame and other products, I do not trust the FDA to not be without bias here - and while I'm not sure I'm on board all the way with the ingredient - the burgers it is made with are very popular and a lot of people say it tastes like meat and would gladly give up meat to have this substitute.
If that sentiment is popular world wide, AND the ingredient is truly safe - this is very big food news - it would effect a lot of industries, including heavily hitting the meat industry.