Within the framework of a project which includes biologists, computer scientists and linguists, we aim at implementing a knowledge base on a recently discovered biological phenomenon. To ascertain the validity of the knowledge extracted from biological literature and to use it to semantically annotate the contents, we address the temporal, modal and/or enunciative characteristics of the identified information. This work answers a specific need expressed by the biologists regarding the quality of the information extracted and recombined for them in the knowledge base.