Jon Corzine’s brokerage firm MF Global Holdings filed for bankruptcy protection Monday following risky bets on debt issued by Italy, Portugal and Spain. MF Global becomes the largest U.S. casualty of Europe’s debt crisis, and the seventh-largest bankruptcy by assets in U.S. history. On Monday, federal investigators discovered as much as $700 million in customer funds missing from the firm. Corzine is a former U.S. senator and New Jersey governor who once ran Goldman Sachs. MF Global employed 2,870 employees worldwide.