Solid-state fermentation production and characterization of an alkaline lipase from a newly isolated Burkholderia gladioli strain

Abstract

The newly isolated Burkholderia gladioli BRM58833 strain was shown to secrete an alkaline lipase highly active and stable in organic solvents. Lipase production was optimized through the cultivation of the strain by solid-state fermentation in wheat bran. The lipase extraction conditions were also optimized. The low-cost extract obtained has shown a high hydrolytic activity of 1096.7 ± 39.3 U·gds^-1 (units per gram of dry solids) against pNPP and 374.2 ± 20.4 U·gds^-1 against triolein. Proteomic analysis revealed the optimized extract is composed of two esterases and three true lipases, showing a preference for long-chain substrates. The highest activity was obtained at 50 °C and pH 9. However, the extract maintained more than 50% of its maximum activity between pH 8.0 and 10.0 and throughout the whole temperature range evaluated (32-70 °C). The enzymes were inhibited by SDS, EDTA, ZnSO₄ and FeCl₃ and activated by FeSO₄, MgCl₂ and BaCl₂. The lipases conserved their activity when incubated in solvents as acetonitrile, diethyl ether, n-heptane n-hexane, toluene, methanol and t-butanol. The resistance of these lipases to solvents and expressive thermostability when compared to other lipases, reveal their potential both in hydrolysis reactions and in synthesis of esters.

Keywords: Burkholderia gladioli; Solid-state fermentation; lipase; process optimization.