Could someone please please help me with research in this area?

JOANNES DEAO - Christened - 17 FEB 1809 Dom Katholisch, Mainz, Rheinhessen, Hessen

I am trying to get further information on this surname that I found on FamilySearch.org. I viewed the microfilm, and the spelling DID look like DEAO, which is extremely rare. I would like to find this person again in Germany, but I didn't know where to begin. Thank you for your help.

Kathleen Deao