Holtmann leaves Mainz after four years, having previously played for Braunschweig, having made just 29 appearances for the Bundesliga club.
Tuesday was a busy day in the 2. Bundesliga with six teams bringing in new players as the countdown to the new season continues.
Both had been training with the first team since the restart in May, and each has now been handed a two-year contract.
The central defender left Fortuna Düsseldorf after seven years and has signed a two-year contract at the Wildparkstadion
Karlsruher SC have made their first new signings of the summer, with Benjamin Goller and Markus Kuster arriving.
Karlsruher SC have finally confirmed that Christian Eichner will continue as head coach after securing the club’s survival.
Were Bielefeld worthy champions? Did Stuttgart deserve promotion? What can their points totals tell us?
Karlsruher SC have confirmed that Jerôme Gondorf will stay at the club following the club securing 2. Bundesliga survival – but four leave the club.
Thursday was another busy day in the 2. Bundesliga with clubs confirming new deals and departures.
In a dramatic final day in the 2. Bundesliga, Karlsruher SC came from behind to beat SpVgg Greuther Fürth and condemn 1. FC Nürnberg to a play-off.