SEOUL (Reuters) - South Korean portal operator Daum Communications said on Monday that it plans to merge with mobile messenger service provider Kakao Corp in October to beef up core businesses and create synergies. The merge ratio will be 1:1.5557456 for Daum and Kakao Corp, Daum said in a regulatory filing. (Reporting By Hyunjoo Jin and Sohee Kim; Editing by Andrea Ricci)