The joint venture between LifePoint Hospitals and Duke University has signed a non-binding agreement to take over a fifth hospital in a deal that would take the Brentwood-based company into Michigan for the first time. Duke LifePoint officials say their memorandum of understanding with the administrators of Marquette General Health System helps pave the way for a formal acquisition agreement later this spring. Marquette General Hospital, the flagship of MGHS, has 290 beds and posted a 2010 profit of about $7 million on revenues of $517 million.