Characterisation of Streptomyces violascens OC125-8 lipase for oily wastewater treatment

Abstract

In this study, the lipase-producing bacterium Streptomyces violascens (GenBank number MF621564) was identified, and the extracellular S. violascens OC125-8 lipase produced by this strain was characterised for use in wastewater treatment. The lipase was partially purified by ammonium sulphate precipitation at a final yield of 3.28-fold purification and a recovery of 56%. The S. violascens OC125-8 lipase exhibited optimum catalytic activity at 40 degrees C and pH 8.0; it was stable at 30-40 degrees C with more than 86% residual activity after 1h; it was also stable over a relatively broad pH range of pH 7.0-11.0, retaining 83.3-100% activity. V-max and K-m values were calculated as 0.61 mu mol/min/mg and 0.259mM, respectively. Enzyme activity significantly increased in the presence of Fe2+ ion but was inhibited by Ca2+, Mn2+, Cu2+ and Mg2+. The addition of a serine protease inhibitor, phenylmethylsulfonyl fluoride (PMSF), strongly inhibited enzyme activity while ethylenediaminetetraacetic acid (EDTA), a metal chelating agent, had no inhibitory effect. The enzyme was fairly stable in the presence of surfactants as well as sodium perborate. Examination of commercial detergent tolerance revealed that the lipase was strongly stable in Tursil (88%), Pril (97%) and Fairy (98.5%), while the lipase was activated in Omo (113.4%) and Ariel (128.3%). Moreover, the lipase showed highest activity towards olive oil (100%), sunflower oil (90%) and burned sunflower oil (55%), while corn oil (44%) and burned olive oil (15%) were less hydrolysed by the enzyme. These properties demonstrate that S. violascens OC125-8 lipase is an ideal choice for oily wastewater management.