Identification and characterisation of a gene encoding aminoacylase activity from Lactococcus lactis MG1363

Development of a One-Step Multiplex PCR Assay for Differential Detection of Four species (Enterobacter cloacae, Enterobacter hormaechei, Enterobacter roggenkampii, and Enterobacter kobei) Belonging to Enterobacter cloacae Complex With Clinical Significance

Enterobacter cloacae complex (ECC) is composed of multiple species and the taxonomic status is consecutively updated. In last decades ECC is frequently associated with multidrug resistance and become an important nosocomial pathogen. Currently, rapid and accurate identification of ECC to the species level remains a technical challenge, thus impedes our understanding of the population at the species level. Here, we aimed to develop a simple, reliable, and economical method to distinguish four epidemiologically prevalent species of ECC with clinical significance, i.e., E. cloacae, E. hormaechei, E. roggenkampii, and E. kobei. A total of 977 ECC genomes were retrieved from the GenBank, and unique gene for each species was obtained by core-genome comparisons. Four pairs of species-specific primers were designed based on the unique genes. A total of 231 ECC clinical strains were typed both by hsp60 typing and by species-specific PCRs. The specificity and sensitivity of the four species-specific PCRs ranged between 96.56% and 100% and between 76.47% and 100%, respectively. The PCR for E. cloacae showed the highest specificity and sensitivity. A one-step multiplex PCR was subsequently established by combining the species-specific primers. Additional 53 hsp60-typed ECC and 20 non-ECC isolates belonging to six species obtained from samples of patients, sewage water and feces of feeding animals were tested by the multiplex PCR. The identification results of both techniques were concordant. The multiplex PCR established in this study provides an accurate, expeditious, and cost-effective way for routine diagnosis and molecular surveillance of ECC strains at species level.

Efficient synthesis of L-phosphinothricin using a novel aminoacylase mined from Stenotrophomonas maltophilia

L-phosphinothricin (L-PPT) is a competitive and environmentally friendly herbicide. To develop an efficient approach for synthesis of l-PPT, a kinetic resolution route with a novel aminoacylase (SmAcy) mined from Stenotrophomonas maltophilia using N-acetyl-PPT as a substrate was first constructed. This SmAcy exhibited high hydrolytic activity and excellent enantioselectivity (E > 200) toward N-acetyl-PPT. Optically pure l-PPT (> 99.9 % ee_p) was acquired with high conversion (> 49 %) within 4 h by the whole cells. On the basis of the docking analysis, a main reason for high enantioselectivity (E > 200) of SmAcy towards l-enantiomer would be that the D-N-acetyl-PPT cannot interact with the key general acid-base residue and the metal ions. A low-cost and simple preparation process of the substrate from commercially available racemic PPT for production of L-PPT was provided. A chemical racemization method of the unreacted D-enantiomer of substrate was also provided to recycle the unwanted substrate enantiomer. This study provides a potential route for the industrial production of L-PPT.

Characterization and application of a L-specific amino acid oxidase from Rhodococcus sp. AIU LAB-3

An L-specific amino acid oxidase (L-AAO) suitable for assay of N-acyl-L-amino acid amidohydrolase (L-aminoacylase) activity was purified from Rhodococcus sp. AIU LAB-3. The enzyme exhibited broad substrate specificity and catalyzed an oxidative deamination of the a-amino group of L-amino acids. The optimal enzyme activities for L-amino acids tested were observed in the pH range from 6.0 to 8.5, and more than 80% of the maximum activity was obtained at pH 7.5. The enzyme was stable in the pH range from 7.0 to 8.5, and the apparent Km values for those L-amino acids were small. We, therefore, developed a new enzymatic method for assay of L-aminoacylase activity using the L-AAO at pH 7.5. The new enzymatic method had advantages that the L-aminoacylase reaction was spectrophotometrically followed by measuring absorbance at 555 nm. The L-aminoacylase activity was assayed within 10 min using a small reaction volume. Thus, the new enzymatic method was simple and sensitive compared to the ninhydrin method.

Genome sequence of Lactobacillus helveticus, an organism distinguished by selective gene loss and insertion sequence element expansion

Mobile genetic elements are major contributing factors to the generation of genetic diversity in prokaryotic organisms. For example, insertion sequence (IS) elements have been shown to specifically contribute to niche adaptation by promoting a variety of genetic rearrangements. The complete genome sequence of the cheese culture Lactobacillus helveticus DPC 4571 was determined and revealed significant conservation compared to three nondairy gut lactobacilli. Despite originating from significantly different environments, 65 to 75% of the genes were conserved between the commensal and dairy lactobacilli, which allowed key niche-specific gene sets to be described. However, the primary distinguishing feature was 213 IS elements in the DPC 4571 genome, 10 times more than for the other lactobacilli. Moreover, genome alignments revealed an unprecedented level of genome stability between these four Lactobacillus species, considering the number of IS elements in the L. helveticus genome. Comparative analysis also indicated that the IS elements were not the primary agents of niche adaptation for the L. helveticus genome. A clear bias toward the loss of genes reported to be important for gut colonization was observed for the cheese culture, but there was no clear evidence of IS-associated gene deletion and decay for the majority of genes lost. Furthermore, an extraordinary level of sequence diversity exists between copies of certain IS elements in the DPC 4571 genome, indicating they may represent an ancient component of the L. helveticus genome. These data suggest a special unobtrusive relationship between the DPC 4571 genome and its mobile DNA complement.

The nisin-controlled gene expression system: Construction, application and improvements

Lactic acid bacteria are widely used in industrial fermentation. The potential use of these bacteria as homologous and heterologous protein expression hosts has been investigated extensively. The NIsin-Controlled gene Expression system (the NICE system) is an efficient and promising gene expression system based on the autoregulation mechanism of nisin biosynthesis in the Lactococcus lactis. In the NICE system, the membrane-located histidine kinase NisK senses the inducing signal nisin and autophosphorylates, then transfers phosphorous group to intracellular response regulator protein NisR which activates nisA promoter to express the downstream gene(s). The NICE system allows regulated overproduction of a variety of interest proteins by several Gram-positive bacteria, especially L. lactis. The essential elements for system construction, its application for expression of some biotechnologically important proteins and further improvements of this system are discussed.

Optimization of the Lactococcus lactis nisin-controlled gene expression system NICE for industrial applications

Background

The nisin-controlled gene expression system NICE of Lactococcus lactis is one of the most widely used expression systems in Gram-positive bacteria. Despite its widespread use, no optimization of the culture conditions and nisin induction has been carried out to obtain maximum yields. As a model system induced production of lysostaphin, an antibacterial protein (mainly against Staphylococcus aureus) produced by S. simulans biovar. Staphylolyticus, was used. Three main areas need optimization for maximum yields: cell density, nisin-controlled induction and protein production, and parameters specific for the target-protein.

Results

In a series of pH-controlled fermentations the following parameters were optimized: pH of the culture, use of NaOH or NH₄OH as neutralizing agent, the addition of zinc and phosphate, the fermentation temperature, the time point of induction (cell density of the culture), the amount of nisin added for induction and the amount of three basic medium components, i.e. yeast extract, peptone and lactose. For each culture growth and lysostaphin production was followed. Lysostaphin production yields depended on all parameters that were varied. In the course of the optimization a three-fold increase in lysostaphin yield was achieved from 100 mg/l to 300 mg/l.

Conclusion

Protein production with the NICE gene expression system in L. lactis strongly depends on the medium composition, the fermentation parameters and the amount of nisin added for induction. Careful optimization of key parameters lead to a significant increase in the yield of the target protein.

Characterization of an aminoacylase from the hyperthermophilic archaeon Pyrococcus furiosus

Aminoacylase was identified in cell extracts of the hyperthermophilic archaeon Pyrococcus furiosus by its ability to hydrolyze N-acetyl-L-methionine and was purified by multistep chromatography. The enzyme is a homotetramer (42.06 kDa per subunit) and, as purified, contains 1.0 +/- 0.48 g-atoms of zinc per subunit. Treatment of the purified enzyme with EDTA resulted in complete loss of activity. This was restored to 86% of the original value (200 U/mg) by treatment with ZnCl(2) (and to 74% by the addition of CoCl(2)). After reconstitution with ZnCl(2), the enzyme contained 2.85 +/- 0.48 g-atoms of zinc per subunit. Aminoacylase showed broad substrate specificity and hydrolyzed nonpolar N-acylated L amino acids (Met, Ala, Val, and Leu), as well as N-formyl-L-methionine. The high K(m) values for these compounds indicate that the enzyme plays a role in the metabolism of protein growth substrates rather than in the degradation of cellular proteins. Maximal aminoacylase activity with N-acetyl-L-methionine as the substrate occurred at pH 6.5 and a temperature of 100 degrees C. The N-terminal amino acid sequence of the purified aminoacylase was used to identify, in the P. furiosus genome database, a gene that encodes 383 amino acids. The gene was cloned and expressed in Escherichia coli by using two approaches. One involved the T7 lac promoter system, in which the recombinant protein was expressed as inclusion bodies. The second approach used the Trx fusion system, and this produced soluble but inactive recombinant protein. Renaturation and reconstitution experiments with Zn(2+) ions failed to produce catalytically active protein. A survey of databases showed that, in general, organisms that contain a homolog of the P. furiosus aminoacylase (> or = 50% sequence identity) utilize peptide growth substrates, whereas those that do not contain the enzyme are not known to be proteolytic, suggesting a role for the enzyme in primary catabolism.