( We ( ( ( know now ) ( that ( ( Lyme disease ) ( is ( ( ( ( an infection ) ( caused ( by ( the bacterium ) ) ) ) ( -LRB- ( spirochete -RRB- ) ) ) ( Borrelia burgdorferi ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP We)) (VP (VBP know) (ADVP (RB now)) (SBAR (IN that) (S (NP (NNP Lyme) (NN disease)) (VP (VBZ is) (NP (NP (NP (DT an) (NN infection)) (VP (VBN caused) (PP (IN by) (NP (DT the) (NN bacterium))))) (PRN (-LRB- -LRB-) (S (VP (VB spirochete))) (-RRB- -RRB-)) (NP (NNP Borrelia) (NNP burgdorferi))))))) (. .)))
We know now that Lyme disease is an infection caused by the bacterium (spirochete) Borrelia burgdorferi.
(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.