Alert reader (I’ve always wanted to say that) Frank writes in to say that he recalled seeing news articles about bacteria being a cause of the rash of deformed frogs. I did a little more Googling, and found that bacteria has in fact been suspected as a cause of the Minnesota frogs’ deformity:
[A] parasite called a trematode may be involved in some frog deformities. Trematodes burrow into the limb buds of tadpoles and can, in fact, cause at least one of the deformities seen in Minnesota frogs.
A study by Gee Chow, “Pesticides and the Mystery of Deformed Frogs,” JOURNAL OF PESTICIDE REFORM Vol. 17, No. 3 (Fall 1997), pg. 14, was cited as the source of that information. However, others have disputed this. A pesticide called methoprene, used for mosquito control, is considered the leading contender for the deformities, but researchers have not fully ruled out parasites and pathogens. So stay tuned.
UPDATE: Paul Orwin informs me that trematodes, though classified as microorganisms, are not bacteria. Read the comments for a fuller explanation. Thanks, Paul!