Left in the dust by Barnes & Noble and Amazon.com, Borders Group Inc.—the second-largest U.S. book chain—may file for bankruptcy as soon as next week, sources said Tuesday. The company will most likely have to close at least 150 of their superstores. A Borders spokesperson declined to comment, but instead referred to a Jan. 27th statement that said the company is “doing everything possible” to avoid defaulting on its payments to vendors and publishers. Borders has posted almost $800 million in losses since 2006, due in part to the chain’s slow embrace of digital reading. Borders shares plummeted 36 percent by the close of the market Tuesday, its largest decline since December 2008.