Esterase production by Aureobasidium pullulans URM 7059 in stirred tank and airlift bioreactors using residual biodiesel glycerol as substrate

Aureobasidium pullulans URM 7059 produced esterase using residual glycerol from biodiesel as the sole carbon source. The culture medium containing residual glycerol (0.1 % v/v), (NH4)(2)SO4 (4 g/L), and yeast extract (8 g/ L) resulted in the highest esterase production using shake-flasks. The enzyme exhibited a molar mass of 50 kDa and was stable at neutral pH and temperatures below 30 degrees C. The cations Cu2+ and Al3+ did not affect the esterase activity, while Ca2+ promoted the highest activity loss. The enzyme kinetic parameters were determined using different substrates (p-nitrophenylcaprylate and p-nitrophenylbutyrate). K-m and V-max were 1.4 mM and 218 mu mol min(-1) for p-NPC, and 1.55 mM and 76.7 mu mol min(-1) for p-NPB. The esterase production was further evaluated using stirred tank and 2-L airlift bioreactors. The airlift reactor operating at the highest air flow rate (8 L/min) increased the enzyme productivity 3-fold compared to the shake-flasks experiments. However, the crude enzymatic extract showed 3 active protein bands by zymography with molecular masses of 172 kDa, 66 kDa, and 40 kDa approximately, suggesting that the pattern of enzyme production changed due to aeration. The crude enzyme degraded the MACO-Sty biopolymer in 14 days, being stable in a wide range of pH (7.0-9.0) and temperatures (40 degrees C - 80 degrees C). The results suggest that this enzyme is a promising catalyst in remediation processes.