A new investor has showed 'serious interest' in acquiring the insolvent German department-store chain Karstadt, administrators told newspaper Frankfurter Allgemeine on Sunday. According to Karstadt's insolvency administrator Klaus Hubert Görg, the company has decided to extend the bidding period until May 28 from the previous deadline of April 28 after receiving an expression of interest from an unnamed investor. A formal offer has yet to be submitted, he added.