EXPLORING LEVAN-PRODUCING BACTERIA CHROMOHALOBACTER JAPONICUS BK-AB 18 FOR BIOBENEFICIATION OF BAUXITE THROUGH THE INVESTIGATION OF ITS LEVANSUCRASE PROPERTIESRUKMAN HERTADI, DARIS QODARISMAN NASIR AND NANDANG MUFTIAbstract Present study shows that the potential application of levan-producing bacteria Chromohalobacter japonicus BK-AB 18 to reduce iron content in a bauxite sample (bio-beneficiation) evaluated by characterizing its extracellular levansucrase, an enzyme that catalyzes levan production. Extracellular levansucrase produced by growing the bacteria in a modified Belghith medium [1 % tryptone, 0.5 % yeast extract, 0.25 % K2HPO4, 7.5 % (w/v) NaCl and 7.5 % (w/v) sucrose] in a rotary shaker overnight, at 37 °C and 150 rpm. The partial purified enzyme has molecular weight of about 50 kDa and exhibited optimum activity at pH 6, 55 °C and 5 % NaCl. Levansucrase activity enhanced up to 18 % by the presence of Ca2+ and Co2+ ions but strongly inhibited by Si2+, Fe3+ and Zn2+ ions. A biobeneficiation potential of the bacteria was evaluated by growing it in the Belghith medium containing 1% (w/v) of a bauxite sample. The amount of iron bound by levan produced by the bacteria quantified periodically with atomic adsorption spectroscopy. Values were found to plateau after 24 hours of biobeneficiation. The iron content in the bauxite sample decreased by 20 % after 48 hours of biobeneficiation. This result suggests that levansucrase produced by C. japonicus BK-AG 18 was relatively active throughout the bio-beneficiation process and has not significantly inhibited by impurities in the bauxite sample.
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