Arginine and Citrulline Catabolic Pathways Encoded by the arc Gene Cluster of Lactobacillus brevis ATCC 367

High concentrations of l-arginine or l-citrulline in the growth medium provided the wine bacterium Lactobacillus brevis with a significant growth advantage. The arginine deiminase pathway (ADI) arc gene cluster of Lactobacillus brevis contains three genes-arcD, arcE1, and arcE2-encoding putative l-arginine/l-ornithine exchangers. Uptake experiments with Lactococcus lactis cells expressing the genes showed that all three transported l-ornithine with affinities in the micromolar range. Similarly, ArcD and ArcE2 transported l-arginine, while ArcE1 transported l-citrulline, an intermediate of the ADI pathway. Chase experiments showed very efficient exchange of l-arginine and l-ornithine by ArcD and ArcE2 and of l-citrulline and l-ornithine by ArcE1. Low affinities (millimolar range) combined with low translocation rates were found for ArcD and ArcE2 with l-citrulline and for ArcE1 with l-arginine. Resting cells of Lactobacillus brevis grown in the presence of l-arginine and l-citrulline rapidly consumed l-arginine and l-citrulline, respectively, while producing ammonia and l-ornithine. About 10% of l-arginine degraded was excreted by the cells as l-citrulline. Degradation of l-arginine and l-citrulline was not subject to carbon catabolite repression by glucose in the medium. At a high medium pH, l-citrulline in the medium was required for induction of the l-citrulline degradation pathway. Pathways are proposed for the catabolic breakdown of l-arginine and l-citrulline that merge at the level of ornithine transcarbamylase in the ADI pathway. l-Arginine uptake is catalyzed by ArcD and/or ArcE2, l-citrulline by ArcE1. l-Citrulline excretion during l-arginine breakdown is proposed to be catalyzed by ArcD and/or ArcE2 through l-arginine/l-citrulline exchange.IMPORTANCELactobacillus brevis, a bacterium isolated from wine, as well as other food environments, expresses a catabolic pathway for the breakdown of l-citrulline in the medium that consists of the l-citrulline/l-ornithine exchanger ArcE1 and part of the catabolic arginine deiminase (ADI) pathway enzymes. The proposed pathways for l-arginine and l-citrulline breakdown provide a mechanism for l-citrulline accumulation in fermented food products that is the precursor of the carcinogen ethyl carbamate.

Ethyl Carbamate Formation Regulated by Lactic Acid Bacteria and Nonconventional Yeasts in Solid-State Fermentation of Chinese Moutai-Flavor Liquor

This study aimed to identify specific microorganisms related to the formation of precursors of EC (ethyl carbamate) in the solid-state fermentation of Chinese Moutai-flavor liquor. The EC content was significantly correlated with the urea content during the fermentation process (R² = 0.772, P < 0.01). Differences in urea production and degradation were found at both species and functional gene levels by metatranscriptomic sequencing and culture-dependent analysis. Lactobacillus spp. could competitively degrade arginine through the arginine deiminase pathway with yeasts, and most Lactobacillus species were capable of degrading urea. Some dominant nonconventional yeasts, such as Pichia, Schizosaccharomyces, and Zygosaccharomyces species, were shown to produce low amounts of urea relative to Saccharomyces cerevisiae. Moreover, unusual urea degradation pathways (urea carboxylase, allophanate hydrolase, and ATP-independent urease) were identified. Our results indicate that EC precursor levels in the solid-state fermentation can be controlled using lactic acid bacteria and nonconventional yeasts.

Convergent evolution of the arginine deiminase pathway: the ArcD and ArcE arginine/ornithine exchangers

The arginine deiminase (ADI) pathway converts L-arginine into L-ornithine and yields 1 mol of ATP per mol of L-arginine consumed. The L-arginine/L-ornithine exchanger in the pathway takes up L-arginine and excretes L-ornithine from the cytoplasm. Analysis of the genomes of 1281 bacterial species revealed the presence of 124 arc gene clusters encoding the pathway. About half of the clusters contained the gene encoding the well-studied L-arginine/L-ornithine exchanger ArcD, while the other half contained a gene, termed here arcE, encoding a membrane protein that is not a homolog of ArcD. The arcE gene product of Streptococcus pneumoniae was shown to take up L-arginine and L-ornithine with affinities of 0.6 and 1 μmol/L, respectively, and to catalyze metabolic energy-independent, electroneutral exchange. ArcE of S. pneumoniae could replace ArcD in the ADI pathway of Lactococcus lactis and provided the cells with a growth advantage. In contrast to ArcD, ArcE catalyzed translocation of the pathway intermediate L-citrulline with high efficiency. A short version of the ADI pathway is proposed for L-citrulline catabolism and the presence of the evolutionary unrelated arcD and arcE genes in different organisms is discussed in the context of the evolution of the ADI pathway.

Novel arginine deiminase-based method to assay L-arginine in beverages

A highly selective and sensitive enzymatic method for the quantitative determination of L-arginine (Arg) has been developed. The method is based on the use of recombinant bacterial arginine deiminase (ADI) isolated from the cells of a recombinant strain Escherichia coli and o-phthalaldehyde (OPA) as a chemical reagent. Ammonia, the product of the enzymatic digestion of Arg by ADI, reacts with OPA and forms in the presence of sulfite a product, which can be detected by spectrophotometry (S) and fluorometry (F). The linear concentration range for Arg assay in the final reaction mixture varies for ADI-OPA-F variant of the method from 0.35 μM to 24 μM with the detection limit of 0.25 μM. For ADI-OPA-S variant of the assay, the linearity varies from 0.7 μM to 50 μM with the detection limit of 0.55 μM. The new method was tested on real samples of wines and juices. A high correlation (R=0.978) was shown for the results obtained with the proposed and the reference enzymatic method.

Application of response surface methodology for optimizing arginine deiminase production medium for Enterococcus faecium sp. GR7

Arginine metabolism in Enterococcus faecium sp. GR7 was enhanced via arginine deiminase pathway. Process parameters including fermentation media and environmental conditions were optimized using independent experiments and response surface methodology (central composite design). Fermentation media (EAPM) were optimized using independent experiments which resulted in 4-fold increase in arginine deiminase specific activity as compared to basal medium. To further enhance arginine deiminase activity in E. faecium sp. GR7 and biomass production including a five-level central composite design (CCD) was employed to study the interactive effect of three-process variables. Response surface methodology suggested a quadratic model which was further validated experimentally where it showed approximately 15-fold increase in arginine metabolism (in terms of arginine deiminase specific activity) over basal medium. By solving the regression equation and analyzing the response surface cartons, optimal concentrations of the media components (g/L) were determined as arginine 20.0; tryptone 15.0; lactose 10.0; K₂HPO₄ 3.0; NaCl 1.0, MnSO₄ 0.6 mM; Tween 80 1%; pH 6.0 for achieving specific arginine deiminase activity of 4.6 IU/mG with concomitant biomass production of 12.1 mg/L. The model is significant as the coefficient of determination (R²) was 0.87 to 0.90 for all responses. Enhanced arginine deiminase yield from E. faecium, a GRAS lactic acid bacterial strain, is desirable to explore in vitro therapeutic potential of the arginine metabolizing E. faecium sp. GR7.

Identification and characterization of Lactobacillus florum strains isolated from South African grape and wine samples

A total of 213 strains of lactic acid bacteria were examined in this study. Among these, 30 strains previously isolated from South African grape and wine samples remained unidentified. The identification of these isolates was performed by BLAST and phylogenetic analyses of 16S rDNA gene sequences, which indicated that the isolates belonged to Lactobacillus florum. In this work, we also designed a discriminative species-specific primer FLOR targeting the 16S rDNA gene of Lb. florum. The validity and specificity of this primer was confirmed. Of particular interest in this study was to further evaluate the identified strains for the presence of genes encoding enzymes of oenological relevance. Reference strains included three flower-associated Lb. florum (F9-1(T), F9-2 and F17) and two Lactobacillus lindneri (AWRI B530 and DSM 20691) strains. Lb. lindneri strains were incorporated as being the closest relatives of Lb. florum. PCR detection results revealed that all Lb. florum strains and Lb. lindneri AWRI B530 (grape isolate) possessed the majority of the tested genes relative to DSM 20691 (beer isolate); these enzyme-encoding genes included malolactic enzyme, peptidases (PepC, PepI, PepN), citrate lyase (α- and β-subunits), phenolic acid decarboxylase and arginine deiminase pathway enzymes (arginine deiminase and ornithine transcarbamylase). Sequence verification of PCR-generated fragments was performed by sequencing. The sequence data were used to construct the phylogenetic trees, which indicated that our Lb. florum isolates cluster with other Lb. florum strains of flower origin but rather distinct from other LAB species, with Lb. lindneri being the next closest species.

Kinetics of the arginine metabolism of malolactic wine lactic acid bacteria Lactobacillus buchneri CUC-3 and Oenococcus oeni Lo111

The excretion of citrulline, a precursor of carcinogenic ethyl carbamate, formed from arginine degradation by malolactic bacteria in wine is of toxicological concern. The arginine metabolism of resting cells of Lactobacillus buchneri CUC-3 and Oenococcus oeni Lo1l1 was examined. The citrulline excretion rate was found to be linearly correlated to the arginine degradation rate. It was possible to calculate an arginine to citrulline conversion ratio which could be used to predict the amount of citrulline expected after the degradation of a known quantity of arginine. The conversion ratios determined in this study were similar to data calculated from other authors for fermentations in wine and ranged between 4.0% and 7.7%. Ribose, fructose and glucose inhibited the degradation of arginine in Lact. buchneri CUC-3, and inhibition of arginine degradation by glucose correlated with higher arginine to citrulline conversion ratios. The work presents new results of arginine metabolism in malolactic bacteria and gives starting points for investigations in wine.

Metabolism of arginine and its positive effect on growth and revival of Oenococcus oeni

Oenococcus oeni is the main lactic acid bacteria species which induces malolactic fermentation during wine-making. It is able to break down arginine via the arginine deiminase pathway, a potential source of energy already considered for many bacteria. The production of ATP by starved cells from arginine was quantified with a bioluminescence assay, and efficient coupling of amino acid catabolism and cell growth was monitored. Therefore, molecular growth yield was determined after glucose exhaustion. With colony plate counting and a direct epifluorescence technique, it was shown that addition of arginine to viable but non-culturable cells obtained after nutrient starvation restored their ability to grow during its degradation. Therefore, arginine produced more than maintenance energy. It is concluded that strains which are able to metabolize arginine might take advantage of this additional energy source for growth.