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* Supervisory board approves exercise of call option
* Lufthansa owns 45 pct of Brussels Airlines already
* Part of plans to boost unit Eurowings via acquisitions (Adds shareholder discontent on price, Brussels Airlinesfigures)
BERLIN, Sept 28 (Reuters) - Lufthansa's supervisory board has approved plans to buy the 55 percent ofBrussels Airlines the German carrier does not own as part of aplan to expand its low-cost airline Eurowings throughacquisitions.
The board is also expected to discuss plans for Lufthansa totake jets for Eurowings from Air Berlin, sources havesaid, to help it become the third largest low-cost airline inEurope after Ryanair and easyJet.
Lufthansa said this year it was discussing how to bringBrussels Airlines, which has 49 planes, into its Eurowingsplatform, which has about 90 planes now.
Brussels Airlines is strong on routes to Africa, where theLufthansa network has gaps, and the German carrier has said itwill look at ways to keep some of the branding.
Lufthansa bought 45 percent of Brussels Airlines owner SNAirholding in 2009 for 65 million euros ($73 million), with anoption to acquire the rest from 2011.
Because Lufthansa has loaned 45 million euros to BrusselsAirlines, the German carrier can buy the rest for as little as2.6 million euros more, which has irked Belgian shareholders ofthe holding firm, Belgian daily Le Soir has reported.
A person familiar with the matter confirmed the figure of2.6 million euros.
The concept for bringing Brussels into the Lufthansa Groupmust now be discussed in detail, a spokesman for the Germanairline said following the supervisory board's decision.
Lufthansa had delayed a decision about whether to exerciseits option to buy all of Brussels Airlines after fatal attacksat the airport and metro system in the Belgian capital in March.
Brussels Airlines served a record 7.5 million passengers in2015 and made a record net profit of 41.3 million euros.Passengers numbers decreased in March and April as a result ofthe attacks but have been recovering since.
The transaction, is expected to be concluded at thebeginning of 2017 after it has held discussions wih SNAirholding shareholders, Lufthansa said in a statement.
($1 = 0.8906 euros) (Reporting by Victoria Bryan; editing by Georgina Prodhan andDavid Clarke)
