Chitin is a carbohydrate (like sugar or starch) that is made of glucose and amino acids. More information and chemical structures can be found at
http://en.wikipedia.org/wiki/Chitin and
http://www.lboro.ac.uk/departments/cg/P ... ction.html (angle tips in the structure are carbon atoms).
http://www.mansfield.ohio-state.edu/~sa ... mpbl05.htm also has information about chitin, as well as other types of macromolecules.
Nitrogen-fixing bacteria live on plant roots and convert nitrogen in the air into ammonia, which the plants can use. Searching "Nitrogen-fixing bacteria" on Google will turn up lots of information about them.
Bacteria and fungi seem to be the organisms that decompose chitin the most. Few protists have chitin in their cell walls, so it is unlikely that a predatory protist would run into it. The Wikipedia article has a sentence about how bacteria digest chitin.
Hope this helps!
Sonia