Efficient recovery of low endotoxin medium-chain-length poly([R]-3-hydroxyalkanoate) from bacterial biomass

Bacterial polyhydroxyalkanoate (PHA) is an attractive biopolyester for medical applications due to its biocompatibility. However, inappropriate extraction of PHA from bacterial biomass results in contamination by pyrogenic compounds (e.g. lipopolysaccharides) and thus influences medical testing. This problem was solved by a temperature-controlled method for the recovery of poly(3-hydroxyoctanoate-co-3-hydroxyhexanaote) (PHO) from Pseudomonas putida GPo1. In contrast to other methods, precipitation of PHO was triggered by cooling the hot solution to a particular temperature. N-hexane and 2-propanol were found to be optimal solvents for such procedure. Quantitative extraction with n-hexane took place at 50 °C and optimal precipitation occurred between 0 and 5 °C. The purity was > 97% (w/w) and the endotoxicity between 10 and 15 EU/g PHO. Additional re-dissolution in 2-propanol at 45 °C and precipitation at 10 °C resulted in a purity of close to 100% (w/w) and the minimal endotoxicity of 2 EU/g PHO. The polydispersity (Mw/Mn) of PHO was decreased from 2.0 to 1.5 for this optimized procedure.