There seems to be no stopping the acquisition tear by Bertelsmann’s BMG Rights Management: It appears to have outbid American Idol creator Simon Fuller to buy Bug — the quirky independent music publishing company whose library includes “What a Wonderful World,” “Fever” and “Happy Together.” Although the companies didn’t disclose the sale price, Reuters said Bug was expected to fetch about $300M. BMG has a lot on its plate: It’s said to still be in the running to buy EMI, the recorded music and publishing powerhouse that Citigroup is auctioning. Early this year it bought publishing rights for Carly Simon and administration rights to Notable Music (which includes musicals such as Sweet Charity and pop hits such as “Sunny”). But with Bug, BMG may have to grapple with a new lawsuit in California Superior Court from singer-songwriter Bruno Mars. He says that his publishing contract with Bug expired early this year when the company faied to renew it before a contractually set deadline. Private equity firm Kohlberg, Kravis & Roberts is a major investor in BMG. Here’s the release announcing the Bug deal:

BERLIN & LOS ANGELES– BMG Rights Management (BMG) and Spectrum Equity Investors (Spectrum) announced today the execution of a definitive agreement under which BMG will acquire Bug Holdings, Inc. and its subsidiary, Bug Music, Inc. (Bug Music), which are controlled by Spectrum and Crossroads Media, Inc. (Crossroads).

Bug Music is a leading independent music publisher. Founded in 1975 and headquartered in Los Angeles, Bug Music currently owns and/or manages copyrights, including evergreen classics and contemporary hits such as “Fever”, “What a Wonderful World”, “I Walk the Line”, “Summer in the City”, “The Real Slim Shady”, “Who Are You?”, “Under the Boardwalk” and “The Passenger”.

Bug Music’s clients include the estates of musical legends Johnny Cash, Willie Dixon, Muddy Waters, Woody Guthrie, Del Shannon and Stevie Ray Vaughan, as well as contemporary icons such as Iggy Pop, Kings of Leon, Ryan Adams, Wilco and The National. Bug Music also supports songwriters and artists through its Arthouse Entertainment joint venture with Kara DioGuardi, 2007 BMI Pop Songwriter of the Year and former American Idol judge.

“With the acquisition of Bug Music and its vast collection of evergreen and contemporary compositions, BMG further establishes itself as a leading music rights management company,” said Hartwig Masuch, CEO of BMG Rights Management. “We look forward to working with Bug Music’s exceptional roster of artists and songwriters.”

“The scope and scale of Bug Music’s catalog today reflects Spectrum’s commitment to investing in profitable franchises with clear potential for growth and then working actively with our partners to accelerate that growth organically and through acquisitions,” said Jim Quagliaroli, Managing Director of Spectrum. “BMG is a true leader in the industry and we have every confidence Bug Music’s artists and assets will be in the right hands and continue on a strong growth path with BMG.”

“We are very pleased that Bug’s artists will find a new home with such a well regarded and rapidly growing rights manager,” said Tom McGrath, Senior Managing Director of Crossroads. “BMG represents the next generation of music publishers who can marshal global resources to develop new writers, showcase the works of established writers and nurture the legacy of Bug’s many long term clients and historic catalogs.”

Financial terms of the transaction, which is expected to close by October and is subject to customary closing conditions, were not disclosed.

J.P. Morgan acted as financial advisor and Latham & Watkins acted as legal advisor to Bug Music.