WordNet sense 1 (a person who supplies information):

informant

WordNet sense 2 (someone who originates or causes or initiates something):

author, generator

WordNet sense 3 (anything (a person or animal or plant or substance) in which an infectious agent normally lives and multiplies):

reservoir

WordNet sense 4 (the place where something begins, where it springs into being):

beginning, origin, root, rootage

WordNet sense 5 (a publication (or a passage from a publication) that is referred to):

reference

WordNet sense 6 (anything that provides inspiration for later work):

germ, seed