Extracellular Degradation of PHA

Biodegradation of PHAs can thus be viewed as two major aspects (1) extracellular degradation of PHA and (2) intracellular degradation of PHAs. 

Group Polymer degraded Representative strains References 

3-hydroxybutyrate 6HX, 6-hydroxyhexanoate 3HO, 3-hydroxyoctanoate 3HV, 3-hydroxy-valerate 3HD, 3-hydroxydecanoate 3HX, 3-hydroxyhexanoate 4HX, 4-hydroxyhexanoate. 

All the enzymes have specific properties which are determined by their structure. All the purified PHA depolymerases show specificity for either PHAscl or PHAmcl- However, they have certain common characteristics. 

The enzyme consists of single polypeptide chain with low molecular weight ( 100 kDa). 

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The mechanism of extracellular degradation of PHA is not yet well understood. A wide variety of microorganisms (fungi, aerobic and anaerobic bacteria) have been implicated but only Pseudomonas lemoignei, Alcaligenes faecalis, and Comamonas sp. have been studied in detail. Production of extracellular PHA depolymerases is induced by the presence of PHA as the sole carbon source. Generally, a PHB depolymerase acts from the hydroxyl terminus to form dimers (or trimers, depending on the depolymerase) and a trace amoimt of monomer. An... 

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