MSNBC.com, the joint venture of Microsoft and NBC, is purchasing Newsvine, a startup that enlists "citizen" journalists to post and comment on mainstream media stories, and write articles of their own.

It's the first acquisition in Redmond-based MSNBC.com's 11-year history. Terms of the deal were not disclosed. Newsvine's investors, who were happy about the deal, put up $1.5 million to get the service going two years ago.