glyA Gene Research Articles

Molecular Characterization of the glyA Gene From the Clinical Isolates of Tannerella forsythia.

TheglyA gene in Tannerella forsythia is attributed for its virulence by producing the enzyme serine hydroxymethyltransferase (SHMT), which plays a vital role in bacterial cell metabolism. The study is thus aimed to determine the frequency of the glyA gene from the clinical strains of T. forsythia isolated from periodontitis patients. Forty-five patients with varying degrees of periodontitis were included in the study, and the plaque samples collected from them were anaerobically processed by inoculating onto sterile anaerobic blood agar plates using a gaspak system, with incubation at 37°C for 5-7 days. The DNA was extracted from the obtained isolated colony, and PCR was performed to confirm the presence of the glyA gene. In total, 46.6% (n= 7) of the cases in group III aggressive periodontitis (n = 15) and 6.66% (n =1) in group II stage II periodontitis (n = 15) showed the presence of T. forsythia,and among them, 57.14% (n= 4) showed the presence of theglyA gene. Conclusion: The findings of the study showed that theglyA gene may be associated with the pathogenesis of T. forsythia and could be thus a novel candidate for the future theragnostic approach to combat periodontitis.

Light Intensity Modulates the Functional Composition of Leaf Metabolite Groups and Phyllosphere Prokaryotic Community in Garden Lettuce (Lactuca sativa L.) Plants at the Vegetative Stage.

Light intensity primarily drives plant growth and morphogenesis, whereas the ecological impact of light intensity on the phyllosphere (leaf surface and endosphere) microbiome is poorly understood. In this study, garden lettuce (Lactuca sativa L.) plants were grown under low, medium, and high light intensities. High light intensity remarkably induced the leaf contents of soluble proteins and chlorophylls, whereas it reduced the contents of leaf nitrate. In comparison, medium light intensity exhibited the highest contents of soluble sugar, cellulose, and free amino acids. Meanwhile, light intensity resulted in significant changes in the composition of functional genes but not in the taxonomic compositions of the prokaryotic community (bacteria and archaea) in the phyllosphere. Notably, garden lettuce plants under high light intensity treatment harbored more sulfur-cycling mdh and carbon-cycling glyA genes than under low light intensity, both of which were among the 20 most abundant prokaryotic genes in the leaf phyllosphere. Furthermore, the correlations between prokaryotic functional genes and lettuce leaf metabolite groups were examined to disclose their interactions under varying light intensities. The relative abundance of the mdh gene was positively correlated with leaf total chlorophyll content but negatively correlated with leaf nitrate content. In comparison, the relative abundance of the glyA gene was positively correlated with leaf total chlorophyll and carotenoids. Overall, this study revealed that the functional composition of the phyllosphere prokaryotic community and leaf metabolite groups were tightly linked in response to changing light intensities. These findings provided novel insights into the interactions between plants and prokaryotic microbes in indoor farming systems, which will help optimize environmental management in indoor farms and harness beneficial plant-microbe relationships for crop production.

Rational Metabolic Engineering Combined with Biosensor-Mediated Adaptive Laboratory Evolution for l-Cysteine Overproduction from Glycerol in Escherichia coli

l-Cysteine is an important sulfur-containing amino acid with numerous applications in the pharmaceutical and cosmetic industries. The microbial production of l-cysteine has received substantial attention, and the supply of the precursor l-serine is important in l-cysteine biosynthesis. In this study, to achieve l-cysteine overproduction, we first increased l-serine production by deleting genes involved in the pathway of l-serine degradation to glycine (serine hydroxymethyl transferase, SHMT, encoded by glyA genes) in strain 4W (with l-serine titer of 1.1 g/L), thus resulting in strain 4WG with l-serine titer of 2.01 g/L. Second, the serine-biosensor based on the transcriptional regulator NCgl0581 of C. glutamicum was constructed in E. coli, and the validity and sensitivity of the biosensor were demonstrated in E. coli. Then 4WG was further evolved through adaptive laboratory evolution (ALE) combined with serine-biosensor, thus yielding the strain 4WGX with 4.13 g/L l-serine production. Moreover, the whole genome of the evolved strain 4WGX was sequenced, and ten non-synonymous mutations were found in the genome of strain 4WGX compared with strain 4W. Finally, 4WGX was used as the starting strain, and deletion of the l-cysteine desulfhydrases (encoded by tnaA), overexpression of serine acetyltransferase (encoded by cysE) and the key enzyme of transport pathway (encoded by ydeD) were performed in strain 4WGX. The recombinant strain 4WGX-∆tnaA-cysE-ydeD can produce 313.4 mg/L of l-cysteine using glycerol as the carbon source. This work provides an efficient method for the biosynthesis of value-added commodity products associated with glycerol conversion.

Molecular Detection ofArcobacterin Human Stool Samples Using Housekeeping Genes

Background: Arcobacter is one of the most common bacteria in humans and livestock, leading to gastroenteritis in humans as well as genital and enteric diseases in animals. This bacterium is known to be the main cause of diarrhea. In molecular studies, the 16SrRNA gene was primarily used as the standard gene for the determination of the Arcobacter. The purpose of this study was to investigate the molecular detection of Arcobacter using glyA, atpA, and gyrA genes compared to16SrRNA. Methods: In this study, 61 samples of Arcobacter DNA isolated from fecal specimens of patients and healthy individuals in the sample bank were used. In order to detect Arcobacter, the intended primers for 16SrRNA as well as glyA, atpA, and gyrA genes were used for polymerase chain reaction (PCR). The products obtained from the PCR were sequenced. Results: The results of the proliferation reactions indicated the accuracy of the intended primers and the associated molecular experiments. Our results showed that 65.57% of the cases were detected to be positive for Arcobacter among 61 samples using the glyA gene. This percentage was higher compared to 16SrRNA (42.62%), gyrA (42.62%), and atpA (24.59%). The analysis was statistically significant. Conclusions: Given the presence of repetitive sequences in the 16SrRNA in most bacteria, the interpretation of the results is likely to be difficult for researchers. The results of this study showed more sensitivity and accurate diagnosis of Arcobacter using the glyA gene than other studied genes. In diagnostic studies of Arcobacter, the glyA gene is proposed as an alternative to the 16SrRNA.

Establishment of CRISPR interference in Methylorubrum extorquens and application of rapidly mining a new phytoene desaturase involved in carotenoid biosynthesis.

The methylotrophic bacterium Methylorubrum extorquens AM1 holds a great potential of a microbial cell factory in producing high value chemicals with methanol as the sole carbon and energy source. However, many gene functions remain unknown, hampering further rewiring of metabolic networks. Clustered regularly interspaced short palindromic repeat interference (CRISPRi) has been demonstrated to be a robust tool for gene knockdown in diverse organisms. In this study, we developed an efficient CRISPRi system through optimizing the promoter strength of Streptococcus pyogenes-derived deactivated cas9 (dcas9). When the dcas9 and sgRNA were respectively controlled by medium PR/tetO and strong PmxaF-g promoters, dynamic repression efficacy of cell growth through disturbing a central metabolism gene glyA was achieved from 41.9 to 96.6% dependent on the sgRNA targeting sites. Furthermore, the optimized CRISPRi system was shown to effectively decrease the abundance of exogenous fluorescent protein gene mCherry over 50% and to reduce the expression of phytoene desaturase gene crtI by 97.7%. We then used CRISPRi technology combined with 26 sgRNAs pool to rapidly discover a new phytoene desaturase gene META1_3670 from 2470 recombinant mutants. The gene function was further verified through gene deletion and complementation as well as phylogenetic tree analysis. In addition, we applied CRISPRi to repress the transcriptional level of squalene-hopene cyclase gene shc involved in hopanoid biosynthesis by 64.9%, which resulted in enhancing 1.9-fold higher of carotenoid production without defective cell growth. Thus, the CRISPRi system developed here provides a useful tool in mining functional gene of M. extorquens as well as in biotechnology for producing high-valued chemicals from methanol. KEY POINTS: Developing an efficient CRISPRi to knockdown gene expression in C1-utilizing bacteria CRISPRi combined with sgRNAs pool to rapidly discover a new phytoene desaturase gene Improvement of carotenoid production by repressing a competitive pathway.

Identification and differentiation of Campylobacter isolated from chicken meat using real-time polymerase chain reaction and high resolution melting analysis of hipO and glyA genes.

Background and Aim:Campylobacter species have been recognized as the most frequently identified bacterial cause of human gastroenteritis. The aims of this study were to identify Campylobacter jejuni and Campylobacter coli species isolated from chicken meat and to analyze the differences in the melting curve patterns of both species.Materials and Methods:A total of 105 chicken meat samples collected from slaughterhouses and retailers in six provinces in Indonesia were examined for the isolation and identification of Campylobacter spp. A total of 56 positive isolates of Campylobacter spp. were analyzed using the quantitative real-time polymerase chain reaction and high resolution melting method.Results:The prevalence of Campylobacter spp. in chicken meat was found to be 61.9%. Regarding the identification, 23 isolates (41.07%) were C. jejuni, 22 (39.29%) were C. coli, six (10.71%) were a mix between C. jejuni and C. coli, and five isolates (8.93%) were Campylobacter spp. All the C. jejuni and C. coli isolates produced varied melting curve patterns.Conclusion:The high prevalence of C. jejuni and C. coli in chicken meat in Indonesia indicates a high risk of the incidence of campylobacteriosis in humans.

Prevalence, molecular detection, and virulence gene profiles of Campylobacter species in humans and foods of animal origin.

Background and Aim:Campylobacteriosis is one of the most well-characterized bacterial foodborne infections worldwide that arise chiefly due to the consumption of foods of animal origin such as poultry, milk, and their products. The disease is caused by numerous species within the genus Campylobacter, but Campylobacter jejuni is the most commonly isolated species from established cases of human campylobacteriosis. This study was conducted to determine the prevalence and virulence of Campylobacter isolates from human, chicken, and milk and milk products in Egypt.Materials and Methods:A total of 1299 samples (547 chicken intestine and liver, 647 milk and milk products, and 105 human stool) were collected and microbiologically investigated, confirmed by multiplex polymerase chain reaction (PCR) targeting the 23S rRNA, hipO, and glyA genes specific for Campylobacter spp., C. jejuni, and Campylobacter Coli, respectively, followed by virulence genes (Campylobacter adhesion to fibronectin F [cadF] and cdtB) detection using PCR.Results:About 38.09%, 37.84%, and 8.5% of human stool, chicken, and milk and milk product samples, respectively, were bacteriologically positive, with a total of 302 Campylobacter isolates. All isolates were molecularly confirmed as Campylobacter spp. (100%) where 285 isolates (94.37%) were identified as C. jejuni and 17 isolates (5.62%) as C. coli. Regarding the virulence pattern, all isolates (100%) carried cadF gene while cytolethal distending toxin B gene was definite in 284/302 isolates (94%), concisely, 282/285 (98.94%) C. jejuni isolates, and in 2/17 (11.76%) C. coli isolates.Conclusion:The widespread presence of these highly virulent Campylobacter, especially C. jejuni, proofs the urgent need for the implementation of stringent control, public health, and food protection strategies to protect consumers from this zoonotic pathogen. The availability of information about pathogen virulence will enable enhanced local policy drafting by food safety and public health officials.

PREVALENCE OF CAMPYLOBACTER SPP. AND ITS PATHOGENIC GENES IN POULTRY MEAT, HUMAN AND ENVIRONMENT IN ASWAN, UPPER EGYPT

A total of 250 samples including 100 samples from chicken meat, 75 samples human diarrhea, 75 samples from environment were collected from Aswan, Egypt. All samples were bacteriologically and biochemically examined for isolation, identification and differentiation of campylobacter spp., multiplex PCR detection of 23S rRNA, hipO, glyA gene for identification and differentiation of campylobacter spp. and detection of some pathogenic virulence genes include Iam, cdtB and cadF genes. Prevalence of campylobacter in chicken meat, human diarrhea and environmental samples by conventional methods were 32%, 14.7% and 13.3%, respectively. Prevalence of campylobacter in chicken meat, human diarrhea and environmental samples by mPCR were 6%, 5.33% and 4%, respectively. About 64.3%, 21.4% and 14.3 of examined samples were Campylobacter jejuni, Campylobacter coli and mixed culture, respectively. Most positive samples contain high prevalence of pathogenic virulence genes. Poultry meat and environment could be a dangerous source for pathogenic campylobacter for human. Most campylobacter isolates have a lot of pathogenic genes which increase the invasiveness and pathogenicity of Campylobacter.

Structural and functional insight into serine hydroxymethyltransferase from Helicobacter pylori.

Serine hydroxymethyltransferase (SHMT), encoded by the glyA gene, is a ubiquitous pyridoxal 5’-phosphate (PLP)-dependent enzyme that catalyzes the formation of glycine from serine. The thereby generated 5,10-methylene tetrahydrofolate (MTHF) is a major source of cellular one-carbon units and a key intermediate in thymidylate biosynthesis. While in virtually all eukaryotic and many bacterial systems thymidylate synthase ThyA, SHMT and dihydrofolate reductase (DHFR) are part of the thymidylate/folate cycle, the situation is different in organisms using flavin-dependent thymidylate synthase ThyX. Here the distinct catalytic reaction directly produces tetrahydrofolate (THF) and consequently in most ThyX-containing organisms, DHFR is absent. While the resulting influence on the folate metabolism of ThyX-containing bacteria is not fully understood, the presence of ThyX may provide growth benefits under conditions where the level of reduced folate derivatives is compromised. Interestingly, the third key enzyme implicated in generation of MTHF, serine hydroxymethyltransferase (SHMT), has a universal phylogenetic distribution, but remains understudied in ThyX-containg bacteria. To obtain functional insight into these ThyX-dependent thymidylate/folate cycles, we characterized the predicted SHMT from the ThyX-containing bacterium Helicobacter pylori. Serine hydroxymethyltransferase activity was confirmed by functional genetic complementation of a glyA-inactivated E. coli strain. A H. pylori ΔglyA strain was obtained, but exhibited markedly slowed growth and had lost the virulence factor CagA. Biochemical and spectroscopic evidence indicated formation of a characteristic enzyme-PLP-glycine-folate complex and revealed unexpectedly weak binding affinity of PLP. The three-dimensional structure of the H. pylori SHMT apoprotein was determined at 2.8Ǻ resolution, suggesting a structural basis for the low affinity of the enzyme for its cofactor. Stabilization of the proposed inactive configuration using small molecules has potential to provide a specific way for inhibiting HpSHMT.

Improved catalytic properties of a serine hydroxymethyl transferase from Idiomarina loihiensis by site directed mutagenesis

A novel glyA gene was screened from a marine bacterium, Idiomarina loihiensis encoding a thermo-stable serine hydroxymethyl transferase (SHMT; 418 AA; 45.4 kDa). The activities of wild type (WT) and mutants were analyzed against d-phenylserine using pyrodoxal-5-phosphate (PLP) as cofactor under optimized conditions. Based on homology modelling and molecular docking, several residues were found that may be able to improve the activity of WT-SHMT. Site directed mutagenesis was conducted. The activity and thermostability of the wild type SHMT was improved by two variants H61G and G132P, which showed a noteworthy change in the thermo-stability and activity as compared to WT. To investigate the mechanism of activity of mutants, we combined two residues into one mutant DUAL. WT showed the optimum activity at 50 °C, whereas H61G, G132P and DUAL had the temperature optima of 55, 60 and 60 °C, respectively. These mutants G132P, H61G and DUAL were quite stable at 45 and 55 °C as compared to WT. Dual mutant was relatively more stable at all tested pH(s) while WT loses its activity in alkaline pH(s). Kinetics studies indicated the 1.52, 2.42 and 4.54 folds increase in the kcat value of H61G, G132P and Dual mutants as compared to WT respectively. The molecular docking indicated that hydrophobic interactions are more prominent than hydrogen-bonding and had more influence on ligand binding and active site cavity. The molecular dynamics showed the changed RMSD values for ligand and formation of new hydrogen bonds, hydrophobic interaction which considerably increased the activity and thermo-stability of the mutant proteins as compared to WT. Thus, increased stabilities at higher temperatures and activities can be attributed to new hydrogen bonding, altered active site geometry and increased ligand interactions.

Rapid and Specific Methods to Differentiate Foodborne Pathogens, Campylobacter jejuni, Campylobacter coli, and the New Species Causing Spotty Liver Disease in Chickens, Campylobacter hepaticus.

Campylobacter jejuni and Campylobacter coli play a major role in bacteria-related foodborne illness in humans. Recently, a newly identified species, Campylobacter hepaticus, was shown to be the causative agent of spotty liver disease in chickens. The pathogenic potential of C. hepaticus in humans is unknown. This new species contains genes usually used to detect C. jejuni and C. coli in DNA-based detection methods, such as the hippuricase (hipO) gene and the glyA (serine hydroxymethyltransferase) gene, with a high degree of similarity. Therefore, polymerase chain reaction (PCR) primers used to detect these species need to be evaluated carefully to prevent misidentification of these important Campylobacter species. A multiplex PCR was developed and optimized to simultaneously and specifically identify the presence of C. jejuni, C. coli, and C. hepaticus in chicken samples containing high-complexity microbiota. The assay represents a new diagnostic tool for investigating the epidemiology of Campylobacter colonization in poultry and environmental samples. It may also be applicable to the investigation of Campylobacter contamination in food and in outbreaks of campylobacteriosis.

GlyA gene knock-out in Escherichia coli enhances L-serine production without glycine addition

In E. coli, glyA encodes for serine hydroxymethyltransferase (SHMT), which converts L-serine to glycine. When engineering L-serine-producing strains, it is therefore favorable to inactivate glyA to prevent L-serine degradation. However, most glyA knockout strains exhibit slow cell growth because of the resulting lack of glycine and C1 units. To overcome this problem, we overexpressed the gcvTHP genes of the glycine cleavage system (GCV), to increase the C1 supply before glyA was knocked out. Subsequently, the kbl and tdh genes were overexpressed to provide additional glycine via the L-threonine degradation pathway, thus restoring normal cell growth independent of glycine addition. Finally, the plasmid pPK10 was introduced to overexpress pgk, serA Δ197 , serC and serB, and the resulting strain E4G2 (pPK10) accumulated 266.3 mg/L of L-serine in a semi-defined medium without adding glycine, which was 3.18-fold higher than the production achieved by the control strain E3 (pPK10). This strategy can accordingly be applied to disrupt the L-serine degradation pathway in industrial production strains without causing negative side-effects, ultimately making L-serine production more efficient.

Enhancement of 5-aminolevulinic acid production by metabolic engineering of the glycine biosynthesis pathway in Corynebacterium glutamicum.

To construct a strain of Corynebacterium glutamicum capable of efficiently producing 5-aminolevulinic acid (5-ALA) via the C4 pathway by modification of serine and glycine pathway using glucose as sole carbon source. The recombinant C. glutamicum strain AP2 harboring a codon-optimized hemA gene from Rhodobacter sphaeroides was used as host strain for 5-ALA production. A plasmid harboring the serine operon, which contained serB, serC and the site-specific mutant serA Δ197 , was constructed and introduced into C. glutamicumAP2, leading to an increase of 70% in 5-ALA production. Further overexpression of the glyA gene increased production of 5-ALA by 150% over the control. 5-ALA production was thus significantly enhanced by engineering the glycine biosynthetic pathway. C.glutamicum AG3 produced 3.4±0.2g 5-ALA/l in shake-flask cultures in CGIIIM medium with the addition of 7.5g glycine/l. This is the first report of remodeling the serine and glycine biosynthetic pathway to improve the production of 5-ALA in C. glutamicum.

OCCURRENCE OF CAMPYLOBACTER SPECIES IN CHICKENS BY MULTIPLEX POLYMERASE CHAIN REACTION

The genus Campylobacter is one of great importance to public health because it includes several species that may cause diarrhea. Poultry and poultry products are known as important sources of human campylobacteriosis. 225 samples were collected from (75) chickens including intestinal content (75), liver (75) and skin (75). The overall occurrence of Campylobacter jejuni and Campylobacter coli in chicken by PCR were (5.3% & 17.8%). Multiplex PCR targeting 23S rRNA specific for genus Campylobacter, hip O gene specific for C. jejuni and glyA gene specific for C. coli was used for the confirmation of phenotypically identified C. jejuni and C. coli isolates. It is concluded that PCR was determined to be more specific and rapid than biochemical tests.

Real-time PCR detection of Campylobacter spp.: A comparison to classic culturing and enrichment

The major disadvantage of the current gold standard for detection of the food pathogen Campylobacter, i.e. culturing, is the lengthy procedure. In this study we assessed the use of real-time PCR for detection of Campylobacter. To this end, 926 poultry samples, taken from transport containers and broiler caeca in The Netherlands in 2007, were subjected to three different real-time PCR detection methods: one targeting the Campylobacter jejuni hipO gene, one targeting the Campylobacter coli glyA gene, and one generically targeting Campylobacter spp. 16S rDNA sequence. The PCR results from the three different PCR protocols were compared to the work of Nauta et al. (2009) who analyzed the same set of samples collected from 62 broiler flocks by means of enrichment culturing.The results indicate that the generic 16S campylobacter PCR detection is equally reliable but much faster (4 h instead of ≥2 days) than detection by means of culturing. Moreover, PCR detection targeting the hipO and the glyA gene provide the possibility of C. jejuni and C. coli species discrimination. The generic Campylobacter spp. PCR analysis also confirmed the high incidence of Campylobacter spp. in poultry samples (∼90%) and the species specific PCR showed the simultaneous presence of C. jejuni and C. coli in ∼24% of the samples. Furthermore, the results from the three PCR analyses suggested the occurrence of alternative Campylobacter species in almost 10% of the samples. The campylobacter PCR detection methods reported here can replace traditional culturing because of being quicker and more reliable.

Characterization of a novel serine hydroxymethyltransferase isolated from marine bacterium Arthrobacter sp. and its application on L-serine production

The current L-serine production relies mainly on cellular or enzymatic conversion from the precursor glycine plus a C1 compound. To date, only several reports have been published on L-serine production from glycine and methanol by methylotrophic bacteria with the serine pathway. This work aimed to isolate a novel serine hydroxymethyltransferase (SHMT) from the methanol-using Arthrobacter sp. and use it for L-serine production with the enzymatic conversion method. Here, A novel glyA gene was isolated from the methanol-using Arthrobacter sp. by thermal asymmetric interlaced PCR (TAIL-PCR), encoding a serine hydroxymethyltransferase (SHMT) with 440 amino acids, belonging to the α-family of fold type I, and pyridoxal-5-phosphate (PLP) dependent enzymes. The enzyme was stable in weakly alkali conditions, showing the optimal activity at pH 7.8 and 45 °C, and a 2.75-fold increase in activity over the corresponding enzyme of Escherichia coli. Two methods (resting cells reaction and enzymatic conversion) were employed to produce serine. Using glycine (133 mM) and formaldehyde (13.3 mM) as substrates to produce serine by enzymatic reaction, 93.6 mM L-serine was obtained with a 70.4 % molar conversion rate from glycine to L-serine. Thus, the characteristics of this novel strain and its enzyme suggest that it has the potential for further research and industrial use.

A novel serine hydroxymethyltransferase from Arthrobacter nicotianae: characterization and improving catalytic efficiency by rational design.

BackgroundSerine hydroxymethyltransferase (SHMT) is the key enzyme in L-serine enzymatic production, suggesting the importance of obtaining a SHMT with high activity.ResultsHere, a novel SHMT gene, glyA, was obtained through degenerate oligonucleotide-primed PCR and encoded a novel SHMT with 54.3% similarity to the known SHMT from Escherichia coli. The obtained protein AnSHMT showed the optimal activity at 40°C and pH 7.5, and was more stable in weakly alkali conditions (pH 6.5-8.5) than Hyphomicrobium methylovorum’s SHMT (pH 6.0-7.5), In order to improve the catalytic efficiency of the wild type, the site-directed mutagenesis based on sequences alignment and bioinformatics prediction, was used and the catalytic efficiency of the mutant I249L was found to be 2.78-fold higher than that of the wild-type, with the replacement of isoleucine by leucine at the 249 position.ConclusionsThis research provides useful information about the interesting site, and the application of DOP-PCR in cloning a novel glyA gene.

A novel serine hydroxymethyltransferase from marine bacterium Alcanivorax sp. and its application on enzymatic synthesis of L-serine

Abstract A novel glyA gene from the marine bacterium Alcanivorax sp. was cloned and expressed in Escherichia coli BL21 (DE3). The recombinant glyA encodes a polypeptide of 418 amino acids, which was designated as AdSHMT that shows the highest identity (70%) with a SHMT from Shewanella algae. The purified enzyme showed a single band at about 45 kDa by SDS-PAGE analysis. It was found that AdSHMT exhibited the maximal activity at 50 °C and pH 7.0. The Km, Vmax, and Kcat values of AdSHMT against dl -threo-3-phenylserine were calculated to be 0.097 mol/L, 3.255 μmol/min/mg and 2.451/s, respectively. More importantly, RP-HPLC detection showed that the AdSHMT achieved an 88.37% molecular conversion rate in catalyzing glycine to l -serine, with the final concentration of l -serine being 353.15 mM in the reaction at 35 °C and 22nd hour when the initial concentration of the substrate (glycine) was 0.399 M. The molecular conversion rate of the AdSHMT from the Alcanivorax sp. was 1.26-fold that of the EcSHMT from the E. coli, which is currently applied in industrial production. Therefore, AdSHMT has the potential for industrial applications due to its high enzymatic conversion rate.

Characterization of a serine hydroxymethyltransferase for l-serine enzymatic production from Pseudomonas plecoglossicida

Pseudomonas plecoglossicida, a bacterium strain that exhibits high Serine hydroxymethyltransferase (SHMT) activity, was isolated from the seawater. A full-length glyA encoding SHMT was obtained by a modified thermal asymmetric interlaced-PCR (TRIL-PCR), which consisted of 1,254 bp, encoded a 417 amino acid polypeptide, and shared the highest identity (75 %) with a glyA gene from Acinetobacter radioresistens CMC-1. Recombinant glyA gene was expressed in Escherichia coli BL21 (DE3) and purified by electrophoretic homogeneity. The enzyme showed the optimal activity at pH 8.0 and 40 °C, and remained stable in high alkali conditions. Using SHMT to produce L-serine by catalyzing the reaction of glycine and tetrahydrofolate is one of the most promising routes to synthesize L-serine, achieving 33.4 mM L-serine at the 12th h of the enzymatic reaction with the substrates of glycine (133 mM) and formaldehyde (13.3 mM). The properties make the SHMT a candidate for further enzymatic studies and industrial applications.

Effect of l-Threonine Concentrations on Acetaldehyde Production and glyA Gene Expression in Fermented Milk by Streptococcus thermophilus

Serine hydroxymethyltransferase encoded by the glyA gene, which has been reported to possess threonine aldolase activity, is able to catalyze the conversion of L-threonine to glycine and acetaldehyde. In this study, eight strains of Streptococcus thermophilus strains with good flavor-enhancing property were investigated to evaluate the acetaldehyde production as well as the expression of glyA gene. S. thermophilus strain MGD4–7, with high levels of acetaldehyde production, was selected for the determination of acetaldehyde and for the analysis of glyA gene using quantitative real-time polymerase chain reaction in the presence and absence of L-threonine. The results indicated that the increased acetaldehyde production was linear with increasing L-threonine levels in the fermented milk. Further more, quantitative real-time PCR analysis showed that the glyA gene was upregulated in the fermented milk in the presence of L-threonine. Understanding the degradation pathway from threonine to glycine and acetaldehyde can be applied to control and improve acetaldehyde production in fermented products with S. thermophilus as the starter culture.