Online retail giant Amazon.com has acquired rival retailer Zappos.com.Zappos employs at least 600 people at its Shepherdsville distribution center and store. In an e-mail to employees, Zappos CEO Tony Hseih said the company will be a wholly-owned subsidiary of Amazon and its management and employees will remain.The deal is worth an estimated 847 million dollars, with Amazon becoming Zappos' sole shareholder and exchanging Zappos investors' stock with Amazon stock. Employees will be given cash and stock options as part of the deal.The sale is expected to close this fall.