Sega has acquired Atlus, after buying its parent company--Index Holdings--in a deal thought to be worth around $140 million. This means that Sega now owns the rights to Persona, Trauma Center, Tactics Ogre and all other Atlus brands. The deal also gives Sega control over Atlus' Tokyo office, and all its 400 staff. There's no word at this stage about what will happen to either the Atlus brand or its employees.
Similarly, Sega has not stated how it intends to handle the games that Atlus currently produces. The publisher / developer was founded back in 1986 and is highly regarded in Japan. It has had several video game brands break into western markets too, including Demon's Souls and the Shin Megami Tensei titles, and many of its Japanese games enjoy cult followings all over the world.
After originally acquiring Atlus, Index Holdings declared itself bankrupt in 2006, and was thought to be $200 million in debt. Sega was one of 20 companies interesting in buying Index, and it has now set up a new subsidiary in Tokyo called Sega Dream Corporation to take over Index's operations.