49ers officially sign DL Earl Mitchell, release Antone Exum Jr.

The 49ers defense is starting to get deeper and healthier just in time for the playoffs.

The 49ers on Wednesday officially made the addition of defensive lineman Earl Mitchell. To clear a roster spot, they released safety Antone Exum Jr.

Matt Barrows of the Athletic first reported San Francisco would add the veteran defensive lineman. Mitchell offers an interior presence the 49ers have lacked since DJ Jones went down. Sheldon Day has been getting additional playing time while the coaching staff has tried piecing together a defensive line rotation.

Adding Mitchell and releasing Exum means the 49ers will have extended depth on the line going into the playoffs. It’s unlikely Mitchell will see substantial time, but his ability to plug the middle of the line should help a 49ers run defense that’s struggled through the latter portion of the season.

Exum’s release is also an indication that Jaquiski Tartt is ready for full participation moving forward. The 49ers added the veteran safety after Tartt’s injury against Baltimore in early December. Exum as with the club in camp, released on final roster cuts, re-signed almost immediately, and released in early October before re-signing early last month. He was primarily relegated to special teams work in both stints with the club this season after starting seven games on defense a year ago.

Their move Wednesday is a good sign for the 49ers heading into the playoffs. It means they’ll have more depth along the interior and edges of the defensive front, and they’ll be healthier in the secondary. Those two things should give the 49ers defense a much-needed lift after it stumbled a bit over the final quarter of the season.