( ( Pathogens ( known ( not ( to ( be ( dangerous ( to humans ) ) ) ) ) ) ) ( ( can ( kill ( other species ) ) ) . ) )
(ROOT (S (NP (NP (NNS Pathogens)) (VP (VBN known) (S (RB not) (VP (TO to) (VP (VB be) (ADJP (JJ dangerous) (PP (TO to) (NP (NNS humans))))))))) (VP (MD can) (VP (VB kill) (NP (JJ other) (NNS species)))) (. .)))
Pathogens known not to be dangerous to humans can kill other species.
(ROOT (S (NP (NNP Water)) (VP (MD can) (VP (VB be) (VP (VBN boiled) (S (VP (TO to) (VP (VB kill) (NP (NP (NN giardia)) (CC and) (NP (RBS most) (JJ other) (NNS pathogens))))))))) (. .)))