OPTIMIZED PRODUCTION AND PROPERTIES OF LIGNIN-DEGRADING ENZYMES FROM BACILLUS MEGATERIUM GROWN ON SOME AGRICULTURAL FEEDSTOCKS

Abstract

In this present study, Bacillus megaterium was isolated and screened using minimal salt medium (MSM) with kraft lignin as the sole substrate and methylene blue as the lignolytic dye indicator for decolourization by lignin-degrading bacteria. Optimization of lignolytic enzyme production from Bacillus megaterium using different agricultural feedstocks as carbon source under submerged fermentation was carried out over 216 h cultivation period. Highest degradation of lignin was obtained when Bacillus megateriumwas grown on oil palm empty bunch fruit (55.31%) followed by palm kernel shell and coconut husk. Oil palm empty bunch fruit medium supported highest production of laccase (31.522 U/mg) at 204 h, while coconut husk medium supported highest production of lignin peroxidase (381.534 U/mg) at 168 h. Highest yield of manganese peroxidase (52.585 U/mg) was obtained on palm kernel shell medium at 204 h. For the effect of nitrogen sources on production of lignolytic enzymes, ammonium nitrate supported the highest yield of laccase (30.61 U/mg) by B. megaterium while the other nitrogen sources supported lower laccase yield. Groundnut meal supported the highest yield of lignin peroxidase (310.12 U/mg), while ammonium nitrate supported optimum production of manganese peroxidase (43.97 U/mg) from B. megaterium. Study on physicochemical properties of lignolytic enzymes showed that the enzymes under study exhibited optimum activity at pH 8.0 and 70 oC. The enzymes demonstrated good stability across broad pH (4.0 - 11.0) and temperature range (30 0C– 60 oC). Their activities were enhanced in the presence of Cu2+, Ca2+ Mg2+, Mn2+ and Fe2+. Dye decolourization studies with Bacillus megaterium gave remarkable results as almost 100% decolourization was achieved with all dyes used, the unique properties displayed by these lignolytic enzymes from Bacillus megaterium suggest their potentials for industrial applications.