SANTA CLARA -- All-Pro linebacker NaVorro Bowman missed his second practice in a row on Thursday. His status for the 49ers' exhibition game against the Denver Broncos is not known.Bowman started in the 49ers' first two exhibition games and practiced on Monday and Tuesday, but he missed Wednesday's practice for undisclosed reasons.Cornerback Chris Culliver (knee), running back Brandon Jacobs (knee) and rookie linebackers Cam Johnson (knee) and Kourtnei Brown (leg) did not practice and will not be available for Sunday's game.Culliver is the 49ers' No. 3 cornerback. Perrish Cox or Tramaine Brock will fill that role with the first unit against the Broncos. Jacobs has done enough to earn a spot as a regular-season contributor, 49ers coach Jim Harbaugh said.