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A Pseudomonas putida strain able to accumulate high amount of polyesters of medium-chain-length 3-hydroxyalkanoic acids (PHA_MCl) was isolated from soil in a landfill site using an enrichment technique. Culture condition of the isolated strain for polyester production in a one-step culture was optimized in a mineralsalts medium against pH and concentrations of ammonium sulfate, carbon source(e.g., octanoate), and phosphate. The optimal values for maximal cell growth and PHA accumulation were: pH; 7∼8, (NH_4)_2SO_4; 8mM, octanoate; 40mM. The optimum temperature was in the range of 20∼30℃, which was rather broader than in other bacteria Cell growth was strongly inhibited by the phosphate limitation to less than 1mM. An increase of phosphate concentration above 1mM showed little effect on cell growth and polyester accumulation. When the strain was grown on octanoate under this optimized condition it produced 3.4g dry biomass per liter and yielded 1.7g PHA per liter amounting to 53 wt% of dry cells. The monomer units composing the polyester synthesized from octanoate were 3-hydroxyoctanoate (3HO), 3-hydroxycaproate (3HC), and 3-hydroxybutyrate (3HB) (85:13:2, mole ratio). Other low linear C_3∼C_10 monocarboxylic acids were also tested for polyester production.
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