( ( ( A protein ) ( in ( their blood ) ) ) ( ( kills ( ( the bacterium ) ( that ( causes ( Lyme disease ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT A) (NN protein)) (PP (IN in) (NP (PRP$ their) (NN blood)))) (VP (VBZ kills) (NP (NP (DT the) (NN bacterium)) (SBAR (WHNP (WDT that)) (S (VP (VBZ causes) (NP (JJ Lyme) (NN disease))))))) (. .)))
A protein in their blood kills the bacterium that causes Lyme disease.
(ROOT (S (NP (JJ Lyme) (NN disease)) (VP (VBZ is) (VP (VBN caused) (PP (IN by) (NP (NNS bacteria))))) (. .)))
Lyme disease is caused by bacteria.