Michael David Samuel Gattermann (1748 – 1829) was Kantor in the St. Petri Kirche in Berlin and taught at the Kolnische Gymnasium. He was a pupil of Johann Philipp Kirnberger. He was an educated musician with particular interest for church music.
A comment from einer_von_weitem made it clear that this piece is not by Gattermann, but by Johann Philipp Kirnberger (1721 – 1783). Gattermann was a pupil of Kirnberger and the score I used as source for this score was in all probability a copy Gattermann made of one of the works of his teacher. So, allthough the manuscript is in Gattermann's hand, the piece itself is from Kirnberger.
I'll keep the original description in place; some of the comments would look a bit weird otherwise.