The rhizoplane microorganisms of Melastoma malabathricum , distributing throughout the acid sulfate and peat soils of South Kalimantan, Indonesia, were investigated, using a soft gel media of N-free Winogradsky s mineral solution solidified with 0.3 % gellan gum. Two bacteria, Sphingomonas rosa EC-K013 and Burkholderia cepacia EC-K014 belonging to the subclasses of -and -Proteobacteria, respectively, emerged in the nitrogen-free medium. Inoculation of S. rosa EC-K013 in the M. malabathricum

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... lings grown in N-free, 1/4 Hoagland s No. 2 medium (pH 3.0) resulted in better growth of the seedlings. In the soft gel medium, EC-K013 also stimulated the growth of a root-associating fungus, tentatively identified as Nectria sp. and a nitrogen-fixer, Mesorhizobium sp., suggesting that S. rosa plays an impor tant role in promotion of microfloral devlopment around the rhizosphere of some acidic soil-adapting plants.