sentence2_structure: Lyme disease<>is caused<>by bacteria
sentence1: But Lyme disease is caused by a bacterium named 'Borrelia burgdorfi', named for Burgdorf, Germany where it was first identified, and the bitch showed a positive Lyme Western Blot test.
sentence2: Lyme disease is caused by bacteria.
question: Lyme disease is caused by what kind of organim?