Supermarket firm Sainsbury has made a surprise move into the e-book retail market with the acquisition of HMV's stake in online venture Anobii.Cash-strapped entertainment media retailer HMV is selling its stake in the social network and online retailer of e-books for just £1. As a result of the transaction and additional investment by Sainsbury the supermarket chain will have a 64% stake in Anobii. Other stakeholders in the venture are publishing firms HarperCollins, Penguin and Random House Group (UK).The acquisition continues Sainsbury's encroachment into the growing online and digital entertainment market following the launch of Sainsbury's Entertainment in November 2010, the acquisition of online entertainment company Global Media Vault in October 2011 and the launch of its music download service earlier this year.JH