A Gram-negative bacterium was isolated from the soil and sludge samples

which had high activity for enantioselective hydrolysis of (R

S)-metalaxyl. The strain was identified as Albibacters by 16S rDNA sequence analysis. It was named Albibacters sp. zjut528. At 37℃

15 g·L-1 of the wet cells (81% water content) catalyzed the hydrolysis of (R

S)-metalaxyl at the concentration of 50 g·L-1 for 28h

the yield reached 47.1% and the main product was R-metalaxyl acid with eep > 99.9%. In order to isolate its intracellular esterase

the cells were disrupted by ultrasonic. After centrifugation

the supernatant was treated by ammonium sulfate precipitation

followed by ion-exchange chromatography and gel filtration chromatography. A SDS-PAGE electrophoresis-pure esterase protein was obtained with a molecular mass of about 40×103. Its N-terminal amino acid sequence was determined as NH2-Ala-Ala -Lys-Ala-Pro-Leu-Arg-Leu-Lys-Glu. Its optimum catalytic temperature and pH were 40℃ and 9.0

respectively. The enzyme was stable at 20-40℃ and pH 5.0-10.0. 0.2 mmol·L-1 of Fe2+

Mn2+

Zn2+ can improve its activity

but Fe3+ inhibited it. Its activity was highly improved when some organic solvents

such as acetonitrile

isopropanol

acetone

isopropyl ether

cyclohexane and n-hexane

were added at the concentration of 20% (vol). The Michaelis-Menten kinetics parameters for the enzyme were Vm=0.18 mmol·L-1·min-1

Km=2.29 mmol·L-1 and Kcat=0.85 min-1. A new process for producing R-matalaxyl from R

S-matalaxyl was established by using Albibacters sp. zjut528 cells as the catalyst. First

the cells catalyzed enantioeletive hydrolysis of (R

S)-matalaxyl to produce R-metalaxyl. After reaction

the R-metalaxyl acid and the unreacted S-matalaxyl were separated by extraction. R-Metalaxy acid was esterified with methanol to produce R-metalaxyl. Followed by some separation steps

the final product of R-metalaxy was obtained. Its purity was 96.2% and ee value was 99.3%. The unreacted S-metalaxyl can be reused by racemization. After heated for 6 h at 60℃

its ee value reduced from 99.4% to 4.2%.