LOUISVILLE - Zayo Group LLC, the fast-growing Louisville-based telecommunications company, is set for another expansion as it has reached an agreement to purchase a southeastern telecom for $13.5 million.

Zayo Group's deal is with USCarrier Telecom LLC, an Atlanta-based bandwidth provider. USCarrier has a 3,700-mile fiber-optic network that connects 44 cities in Georgia, Florida, Alabama and Tennessee.

Zayo already had a stake in USCarrier. It acquired about 50 percent of the company through its October 2010 acquisition of American Fiber Systems.

Zayo will make the purchase using cash on hand, according to the release announcing the deal. The transaction is expected to close during the fourth quarter.