DEGRADATION OF POLY(3-HYDROXYOCTANOIC ACID) [P(3HO)] BY BACTERIA - PURIFICATION AND PROPERTIES OF A P(3HO) DEPOLYMERASE FROM PSEUDOMONAS-FLUORESCENS GK13

Twenty-five gram-negative bacteria and one gram-positive bacterium capable of growing on poly(3-hydroxyoctanoic acid) [P(3HO)] as the sole source of carbon and energy were isolated from various soils, lake water, and activated sludge. Most of the isolates degraded only P(3HO) and copolymers of medium-chain-length (MCL) hydroxyalkanoic acids (HA). Except for the gram-positive strain, which was able to hydrolyze P(3HO) and poly(3-hydroxybutyric acid) [P(3HB)], no isolate was able to degrade polymers of short-chain-length HA, such as P(3HB) or poly(3-hydroxyvalerate) [P(3HV)]. All strains utilized a large variety of monomeric substrates for growth. All gram-negative strains, but not the gram-positive strain, accumulated poly(hydroxyalkanoic acids) (PHA), consisting of MCL HA, if they were cultivated under accumulation conditions. One strain, which was identified as Pseudomonas fluorescens GK13 (biovar V), was selected and the extracellular P(3HO) depolymerase of this strain was purified from the culture medium of P(3HO)-grown cells by chromatography with Octyl-Sepharose CL4B and by gel filtration with Superose 12. The relative molecular weights of the native and sodium dodecyl sulfate-treated enzymes were 48,000 and 25,000, respectively. The purified enzyme hydrolyzed P(3HO), copolymers of MCL HA, and para-nitrophenyl esters of fatty acids. P(3HB), P(3HV), and characteristic substrates for lipases, such as Tween 80 or triolein, were not hydrolyzed. The P(3HO) depolymerase of P. fluorescens GK13 was insensitive to phenylmethylsulfonyl fluoride and dithioerythritol, unlike other PHA depolymerases. The dimeric ester of 3-hydroxyoctanoic acid was identified as the main product of enzymatic hydrolysis of P(3HO). The expression of the P(3HO) depolymerase by P. fluorescens GK13 was inducible by P(3HO), various 3- and 2-hydroxy compounds and by MCL fatty acids. However, high enzyme activity was detected only at the end of exponential growth or after cessation of growth.