Isolation of poly(β‐ l ‐malic acid)‐degrading bacteria and purification and characterization of the PMA hydrolase from Comamonas acidovorans strain 7789

Several bacteria were isolated which were able to utilize poly(β‐ l ‐malic acid) as sole carbon source for growth. The poly(β‐ l ‐malic acid) hydrolyzing enzyme of Comamonas acidovorans strain 7789 was detected in the membrane fraction. The enzyme was purified by isolation of crude cell membranes by ultracentrifugation of disrupted cells, solubilization of the membrane fraction with octylglucoside, selective precipitation with 50% saturated ammonium sulfate and preparative isoelectric focusing. SDS‐PAGE analysis revealed a M r of 43 000. The pH optimum was 8.1 and the K m was 0.13 μM (in terms of monomeric units) and 0.0021 μM poly(β‐ l ‐malic acid) at pH 8.1 (100 mM glycylglycine buffer). Addition of NaCl, KCl, CaCl 2 or MgCl 2 (from 25 to 100 mM) decreased the hydrolase activity, whereas EDTA or polymethane sulfonic acid fluoride had no influence on the enzyme. The depolymerization of poly(β‐ l ‐malic acid) proceeded from the ends of the polyester resulting in the formation of l ‐malate. Esterase activity was not detectable with p ‐nitrophenyl acetate or p ‐nitrophenyl butyrate, which is used to determine for example poly(3‐hydroxybutyric acid) depolymerase activity.