Enhancing the degradation of mixed polycyclic aromatic hydrocarbon and medium-chain-length polyhydroxyalkanoate production by mixed bacterial cultures using modified repeated batch fermentation.

AIMS: To increase the biodegradation of phenanthrene (PHE), pyrene (PYR) and fluoranthene (FLU) through mixed cultures of polycyclic aromatic hydrocarbon (PAH)-degrading bacteria, using modified repeated batch fermentation. METHODS AND RESULTS: Novel bacterial strains of Pseudomonas putida, Pseudomonas sp. and Ralstonia eutropha were cultivated and the biodegradation and conversion of mixed PAH to medium-chain-length polyhydroxyalkanoates (MCL-PHA) was determined. The highest degradation of PAH (100%) and PHA production (50·0%) was obtained in medium containing 30 mmol l-1 of mixed PAH after three cycles of repeated batch fermentation. The concentration of PAH in the reactor was increased from 30 to 90 mmol l-1 with repeated additions of PAH, and bacteria were able to produce PHA at 40% of cell dry mass. The MCL-PHA were identified by gas chromatography/mass spectroscopy, with the 3-hydroxydecanoate (3-HD) monomer higher than 75 mol.%. CONCLUSIONS: This study demonstrated that the biodegradation of PHE, PYR and FLU was enhanced by modified repeated batch fermentation using a mixed culture of bacteria. In addition, this fermentation strategy also increased the production of PHA, with an increase in monomer composition. SIGNIFICANCE AND IMPACT OF THE STUDY: This was the first study to describe the enhancement of the degradation of mixed solutions of PHE, PYR and FLU, and PHA production, using novel mixed bacterial cultures and modified repeated batch fermentation. The MCL-PHA formed had uniquely high 3-HD content.

Use of TPP and ATPS for partitioning and recovery of lipase from Pacific white shrimp (Litopenaeus vannamei) hepatopancreas.

Lipase recovery from Pacific white shrimp hepatopancreas using a three-phase partitioning (TPP) system in combination with an aqueous two-phase system (ATPS) was studied. TPP system was formed with a simultaneous addition of salt directly to crude extract (CE) followed by an organic solvent addition. The various process parameters required for efficient purification of lipase were optimized. The best lipase yield (87.41%) and purification fold (PF) (3.49-fold) were obtained in the interphase of TPP system, which consisted of the CE to t-butanol ratio of 1:1 (v/v) in the presence of 50% (w/v) (NH4)2SO4. Subsequently, TPP fraction was subjected to ATPS. Effects of phase compositions including PEG molecular weight and concentration, types and concentration of salts, NaCl addition and system pH on lipase partitioning were investigated. With the application of 25% (w/w) PEG1000 and 15% (w/w) MgSO4, at pH 5.0 was found most appropriate since high lipase PF (5.19-fold) and yield (78.46%) in top phase were obtained. The partitioned enzyme exhibited optimal activity at pH 8.0 and 55 °C and was stable at a temperature range of 0-40 °C and a pH range of 7-10. The partitioned lipase showed high tolerance in the presence of ethanol and methanol. Hence, the combined partitioning systems, TPP-ATPS, were found to be an attractive technique for the recovery and partial purification of lipase from Pacific white shrimp hepatopancreas.