Gelobet seist du, Jesu Christ

Johann Friedrich Alberti (1642-1710) was a German baroque composer and organist. Alberti was born in Tönning, Schleswig. He received his musical training in Leipzig from Werner Fabricius and in Dresden from Vincenzo Albrici. Then he worked as an organist in Merseburg cathedral until his departure in 1698 caused by the paralysis of his right hand because of a stroke. His pupil Georg Friedrich Kauffmann succeeded him as a princely Saxon townsman and cathedral organist at the court of the Saxon duke and Merseburg Cathedral. Alberti's works include chorale preludes, 35 choral arrangements, 12 ricercati (lost) and various sacred works. He died, aged 68, in Merseburg.

The prelude on “Gelobet seist du Jesu Christ” is set up as a fugue. But quite originally, the chorale melody is not used as the subject of the fugue, but as one of the two counter subjects to the main subject of the fugue.
(source: Wikipedia & Partitura Organum)