A DNA fragment from Microbacterium liquefaciens AJ 3912, containing the genes responsible for the conversion of 5-substituted-hydantoins to α-amino acids, was cloned in Escherichia coli and sequenced. Seven open reading frames (hyuP, hyuA, hyuH, hyuC, ORF1, ORF2, and ORF3) were identified on the 7.5 kb fragment. The deduced amino acid sequence encoded by the hyuA gene included the N-terminal amino acid sequence of the hydantoin racemase from M. liquefaciens AJ 3912. The hyuA, hyuH, and hyuC genes were heterologously expressed in E. coli; their presence corresponded with the detection of hydantoin racemase, hydantoinase, and N-carbamoyl α-amino acid amido hydrolase enzymatic activities respectively. The deduced amino acid sequences of hyuP were similar to those of the allantoin (5-ureido-hydantoin) permease from Saccharomyces cerevisiae, suggesting that hyuP protein might function as a hydantoin transporter. 相似文献
A novel esterase catalyzing regioselective hydrolysis was purified from the membrane fraction of Microbacterium sp. 7-1W, and characterized. The enzyme was solubilized with Brij 58 and purified 13.8-fold to apparent homogeneity with 2.58% overall recovery. The relative molecular mass of the native enzyme as estimated by gel filtration was more than 600,000 Da, and the subunit molecular mass was 62,000 Da. The enzyme catalyzed cleavage of the terminal ester bonds of cetraxate esters and pantothenate esters. The K(m) and V(max) values for methyl cetraxate were 0.380 mM and 7.76 micromole min(-1) mg(-1) protein, respectively. The enzyme was inhibited by serine hydrolase inhibitors. 相似文献
Aims: To assess the impact of Bacillus amyloliquefaciens and Microbacterium oleovorans on bacterial and fungal groups associated to the roots of field-grown maize. Methods and Results: Identification and count of bacterial and fungal culturable populations associated to the roots of maize seedlings, changes in culturable community structure according to the richness and diversity indexes concept and shifts in microbial activity through analysis of cellulolytic, ammonification and nitrification potentials were determined, in relation to kernel treatment with biological control agents. Following the treatment of maize kernels with B. amyloliquefaciens at 107 CFU ml−1, an increase in bacterial diversity was observed at the rhizoplane of resultant seedlings. Bacterial richness was significantly increased at the root inner tissues of seedlings treated with Mic. oleovorans . Fusarium , Aspergillus , Penicillium and Trichoderma were the main fungal genera isolated and there population sizes were unequally affected by the addition of biocontrol agents. Conclusions: Numbers and types of isolated bacteria and fungi changed in response to the addition of biocontrol agents, while microbial activity remained unchanged with respect to control. Significance and Impact of the Study: This study provides an insight of the effects of proven biocontrol agents on micro-organisms naturally associated to the target crop. 相似文献
The bioconversion of propionitrile to propionamide was catalysed by nitrile hydratase (NHase) using resting cells of Microbacterium imperiale CBS 498-74 (formerly, Brevibacterium imperiale). This microorganism, cultivated in a shake flask, at 28 °C, presented a specific NHase activity of 34.4 U mgDCW−1 (dry cell weight). The kinetic parameters, Km and Vmax, tested in 50 mM sodium phosphate buffer, pH 7.0, in the propionitrile bioconversion was evaluated in batch reactor at 10 °C and resulted 21.6 mM and 11.04 μmol min−1 mgDCW−1, respectively. The measured apparent activation energy, 25.54 kJ mol−1, indicated a partial control by mass transport, more likely through the cell wall.
UF-membrane reactors were used for kinetic characterisation of the NHase catalysed reaction. The time dependence of enzyme deactivation on reaction temperature (from 5 to 25 °C), on substrate concentrations (from 100 to 800 mM), and on resting cell loading (from 1.5 to 200 μg ml−1) indicated: lower diffusional control (Ea=37.73 kJ mol−1); and NHase irreversible damage caused by high substrate concentration. Finally, it is noteworthy that in an integral reactor continuously operating for 30 h, at 10 °C, 100% conversion of propionitrile (200 mM) was attained using 200 μg ml−1 of resting cells, with a maximum volumetric productivity of 0.5 g l−1 h−1. 相似文献
A pure strain of Microbacterium lacticum DJ-1 capable of anaer-obic biodegradation of ethylbenzene was isolated from soil contaminated with gasoline. Growth of the strain and biodegradation of ethylbenzene in batch cultures led to stoichiometric reduction of nitrate. M. lacticum DJ-1 could degrade 100 mg L?1 of ethylbenzene completely, with a maximum degradation rate of 15.02 ± 1.14 mg L?1 day?1. Increasing the initial concentration of ethy-lbenzene resulted in decreased degradative ability. The cell-specific growth rates on ethylbenzene conformed to the Haldane–Andrew model in the substrate level range of 10–150 mg L?1. Kinetic parameters were determined by nonlinear regression on specific growth rates and various initial substrate concentrat-ions, and the values of the maximum specific growth rate, half saturation constant, and inhibition constant were 0.71 day?1, 34.3 mg L?1, and 183.5 mg L?1, respectively. This is the first report of ethylbenzene biodegradation by a bacterium of Microbacterium lacticum under nitrate-reducing conditions. 相似文献
An enzymatic fluorometric assay for pyridoxal with pyridoxal dehydrogenase was developed. The detection limit was about 10 pmol: the calibration curve of pyridoxal showed high linearity (r=0.993). The values obtained by this method correlated well with those by the HPLC method. The enzyme had a high specificity for pyridoxal, and thus animal samples could be directly analyzed without separation of pyridoxal 5′-phosphate by column chromatography. 相似文献