Arginine catabolism in Lactobacillus sake isolated from meat

Suppression of lactate production by aerobic fed-batch cultures of Lactococcus lactis

Aerobic fed-batch cultures were studied as a means of suppressing the production of lactate, which inhibits the growth of lactic acid bacteria (LAB). LAB produce lactate via lactate dehydrogenase (LDH), regenerating nicotinamide adenine dinucleotide (NAD⁺) consumed during glycolysis. Therefore, we focused on NADH oxidase (NOX), employing oxygen as an electron acceptor, as an alternative pathway to LDH for NAD⁺ regeneration. To avoid glucose repression of NOX and NAD⁺ consumption by glycolysis exceeding NAD⁺ regeneration by NOX, glucose was fed gradually. When Lactococcus lactis MG 1363 was aerobically fed at a specific growth rate of 0.2 h^-1, the amount of lactate produced per amount of grown cell was reduced to 12% of that in anaerobic batch cultures. Metabolic flux analysis revealed that in addition to NAD⁺ regeneration by NOX, ATP acquisition by production of acetate and NAD⁺ regeneration by production of acetoin and 2,3-butanediol contributed to suppression of lactate production.

Suppression of lactate production in fed-batch culture of some lactic acid bacteria with sucrose as the carbon source

We report a method for suppression of lactate production by lactic acid bacteria (LAB) in culture. LAB produce lactate to regenerate NAD⁺ that is consumed during glycolysis. Glucose suppresses NAD⁺ regeneration pathways other than lactate dehydrogenase and non-glycolytic ATP production pathways. Therefore, the carbon source was changed to sucrose, and fed-batch culture was performed to limit the glycolytic flux and thus suppress lactate production. As a result, lactate productivity (i.e., the amount of lactate produced per amount of grown cell) in the sucrose/fed-batch culture was decreased compared to that in glucose/batch culture, in all five LAB strains examined. The productivity level decreased to 24% and 46% in Lactobacillus reuteri JCM 1112 and Lactococcus lactis JCM 7638, respectively. Metabolic flux analysis of Lactobacillus reuteri JCM 1112 revealed increased contributions of the mannitol production pathway to NAD⁺ regeneration and the arginine deiminase pathway to ATP production in the sucrose/fed-batch culture.

Suppression of lactate production by using sucrose as a carbon source in lactic acid bacteria

Lactic acid bacteria (LAB) grow by producing lactate from sugar. However, the accumulation of lactate inhibits their growth. Here, the lactate productivity per cell in a semi-solid medium prepared with a chlorella powder in several LAB strains was much lower than that in the conventional MRS medium. Furthermore, the lactate production was suppressed not only in semi-solid medium, but also in chlorella liquid medium. The lactate productivity by Lactococcus lactis subsp. lactis NBRC 12007 in the chlorella liquid medium and MRS medium was 3.0 and 6.9 g-lactate·g-cell^-1, respectively. The productivity of lactate in the chlorella liquid medium decreased to 44% of that in MRS medium. Gas chromatography/mass spectrometry (GC/MS) analysis of the culture supernatants revealed that the utilization of sucrose in the chlorella powder led to the suppression of lactate production. Comparison of the metabolites extracted from the cells indicated that the two ATP generating pathways, the arginine deiminase pathway and the decarboxylation reaction of glutamate and GABA, which are usually repressed by glucose, are activated in chlorella medium. It was considered that these pathways which do not require NAD⁺ for generation of ATP are not repressed when sucrose is used as a carbon source. Thus, the utilization of these pathways results in the suppression of the lactate production.

Sucrose-Induced Proteomic Response and Carbohydrate Utilization of Lactobacillus sakei TMW 1.411 During Dextran Formation

Lactobacillus (L.) sakei belongs to the dominating lactic acid bacteria in indigenous meat fermentations, while diverse strains of this species have also been isolated from plant fermentations. We could recently show, that L. sakei TMW 1.411 produces a high molecular weight dextran from sucrose, indicating its potential use as a dextran forming starter culture. However, the general physiological response of L. sakei to sucrose as carbohydrate source has not been investigated yet, especially upon simultaneous dextran formation. To address this lack of knowledge, we sequenced the genome of L. sakei TMW 1.411 and performed a label-free, quantitative proteomics approach to investigate the sucrose-induced changes in the proteomic profile of this strain in comparison to its proteomic response to glucose. In total, 21 proteins were found to be differentially expressed at the applied significance criteria (FDR ≤ 0.01). Among these, 14 were associated with the carbohydrate metabolism including several enzymes, which enable sucrose and fructose uptake, as well as, their subsequent intracellular metabolization, respectively. The plasmid-encoded, extracellular dextransucrase of L. sakei TMW 1.411 was expressed at high levels irrespective of the present carbohydrate and was predominantly responsible for sucrose consumption in growth experiments using sucrose as sole carbohydrate source, while the released fructose from the dextransucrase reaction was more preferably taken up and intracellularly metabolized than sucrose. Genomic comparisons revealed, that operons coding for uptake and intracellular metabolism of sucrose and fructose are chromosomally conserved among L. sakei, while plasmid-located dextransucrase genes are present only in few strains. In accordance with these findings, all 59 different L. sakei strains of our strain collection were able to grow on sucrose as sole carbohydrate source, while eight of them exhibited a mucous phenotype on agar plates indicating dextran formation from sucrose. Our study therefore highlights the intrinsic adaption of L. sakei to plant environments, where sucrose is abundant, and provides fundamental knowledge regarding the use of L. sakei as starter culture for sucrose-based food fermentation processes with in-situ dextran formation.

Robust Domination of Lactobacillus sakei in Microbiota During Traditional Japanese Sake Starter Yamahai-Moto Fermentation and the Accompanying Changes in Metabolites

The successful production of sake (Japanese rice wine) is brought about by drastic changes in microbial flora and chemical components during fermentation. In the traditional manufacturing process of sake starter (yamahai-moto), spontaneous growth of lactic acid bacteria suppresses inappropriate microorganisms and prepares the optimum environment for the alcohol fermentative yeast. In this study, we analyzed the changes in bacterial flora and chemical components of yamahai-moto. High-throughput next-generation sequencing (NGS) of the 16S ribosomal RNA gene V4 region revealed that various kinds of bacteria, including nitrate-reducing bacteria, existed in the early fermentation stage; however, Lactobacillus sakei then increased drastically to become dominant in the middle stage. Interestingly, this result was different from that obtained in the previous year at the same manufacturer; the early-stage major bacterium was Lactobacillus acidipiscis. Lactic acid, glucose, isomaltose, and total free amino acids increased throughout the fermentation process, which was attributable to the metabolism of L. sakei and the koji mold. It is noteworthy that significant ornithine accumulation and arginine consumption were observed from the middle to late stages. Thirty-eight percent of the L. sakei isolates from yamahai-moto exhibited significant ornithine production, indicating that the arginine deiminase pathway of L. sakei was working to survive the extremely low pH environment of the moto after the middle stage. This is the first report that includes concurrent analyses of the NGS-based bacterial flora and chemical components of yamahai-moto, providing further knowledge to help understand and improve the process of sake brewing.

Effects of glucose availability in Lactobacillus sakei; metabolic change and regulation of the proteome and transcriptome

Effects of glucose availability were investigated in Lactobacillus sakei strains 23K and LS25 cultivated in anaerobic, glucose-limited chemostats set at high (D = 0.357 h-1) and low (D = 0.045 h-1) dilution rates. We observed for both strains a shift from homolactic towards more mixed acid fermentation when comparing high to low growth rates. However, this change was more pronounced for LS25 than for 23K, where dominating products were lactate>formate>acetate≥ethanol at both conditions. A multivariate approach was used for analyzing proteome and transcriptome data from the bacterial cultures, where the predictive power of the omics data was used for identifying features that can explain the differences in the end-product profiles. We show that the different degree of response to the same energy restriction revealed interesting strain specific regulation. An elevated formate production level during slow growth, more for LS25 than for 23K, was clearly reflected in correlating pyruvate formate lyase expression. With stronger effect for LS25, differential expression of the Rex transcriptional regulator and NADH oxidase, a target of Rex, indicated that maintainance of the cell redox balance, in terms of the NADH/NAD+ ratio, may be a key process during the metabolic change. The results provide a better understanding of different strategies that cells may deploy in response to changes in substrate availability.

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.

Use of response surface method for maximizing the production of arginine deiminase by Pseudomonas putida

•

First report on Arginine deiminase production from Pseudomonas putida using RSM.

•

Optimum conditions for ADI production were established in shake flasks.

•

ADI production was assessed in a 14 L bioreactor under the optimized conditions.

•

Repressor effect of aeration on ADI production was observed in 14 L bioreactor.

•

Substantial improvement of 4.5-folds in ADI titre was achieved.

Statistically designed experiments were used to optimize the production of arginine deiminase (ADI) by Pseudomonas putida KT2440 in batch culture. A Plackett-Burman design involving eleven factors showed that ADI production was most influenced by the initial pH and the initial concentrations of glucose and yeast extract. A central composite experimental design showed that the optimal values of these factors were 8.0, 10 g/L and 12.5 g/L, respectively. The other components of the optimal culture medium were bacto peptone 7.5 g/L, Triton X–100 0.30% (v/v), and arginine 3 g/L, for a culture temperature of 25 °C. Compared with the basal medium, the ADI activity in the optimized medium had nearly 4.5-fold increase (4.31 U/mL). The optimized medium was then used for a further study of ADI production in a 14 L stirred tank bioreactor. The agitation speed and the aeration rates were varied to determine suitable values of these variables.

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.

Expression of the arginine deiminase pathway genes in Lactobacillus sakei is strain dependent and is affected by the environmental pH

The adaptation of Lactobacillus sakei to a meat environment is reflected in its metabolic potential. For instance, the ability to utilize arginine through the arginine deiminase (ADI) pathway, resulting in additional ATP, represents a competitive benefit. In L. sakei CTC 494, the arc operon (arcABCTDR) shows the same gene order and organization as that in L. sakei 23K, the genome sequence of which is known. However, differences in relative gene expression were found, and these seemed to be optimal in different growth phases, namely, the highest relative gene expression level was in the end exponential growth phase in the case of L. sakei CTC 494 and in the mid-exponential growth phase of L. sakei 23K. Also, the environmental pH influenced the relative expression level of the arc operon, as shown for L. sakei CTC 494, with the highest relative expression level occurring at the optimal pH for growth (pH 6.0). Deviations from this optimal pH (pH 5.0 and pH 7.0) resulted in an overall decline of the relative expression level of all genes of the arc operon. Furthermore, a differential relative expression of the individual genes of the arc operon was found, with the highest relative gene expression occurring for the first two genes of the arc operon (arcA and arcB). Finally, it was shown that some L. sakei strains were able to convert agmatine into putrescine, suggesting an operational agmatine deiminase pathway in these strains, a metabolic trait that is undesirable in meat fermentations. This study shows that this metabolic trait is most probably encoded by a previously erroneously annotated second putative arc operon.

Global transcriptome response in Lactobacillus sakei during growth on ribose

BACKGROUND

Lactobacillus sakei is valuable in the fermentation of meat products and exhibits properties that allow for better preservation of meat and fish. On these substrates, glucose and ribose are the main carbon sources available for growth. We used a whole-genome microarray based on the genome sequence of L. sakei strain 23K to investigate the global transcriptome response of three L. sakei strains when grown on ribose compared with glucose.

RESULTS

The function of the common regulated genes was mostly related to carbohydrate metabolism and transport. Decreased transcription of genes encoding enzymes involved in glucose metabolism and the L-lactate dehydrogenase was observed, but most of the genes showing differential expression were up-regulated. Especially transcription of genes directly involved in ribose catabolism, the phosphoketolase pathway, and in alternative fates of pyruvate increased. Interestingly, the methylglyoxal synthase gene, which encodes an enzyme unique for L. sakei among lactobacilli, was up-regulated. Ribose catabolism seems closely linked with catabolism of nucleosides. The deoxyribonucleoside synthesis operon transcriptional regulator gene was strongly up-regulated, as well as two gene clusters involved in nucleoside catabolism. One of the clusters included a ribokinase gene. Moreover, hprK encoding the HPr kinase/phosphatase, which plays a major role in the regulation of carbon metabolism and sugar transport, was up-regulated, as were genes encoding the general PTS enzyme I and the mannose-specific enzyme II complex (EIIman). Putative catabolite-responsive element (cre) sites were found in proximity to the promoter of several genes and operons affected by the change of carbon source. This could indicate regulation by a catabolite control protein A (CcpA)-mediated carbon catabolite repression (CCR) mechanism, possibly with the EIIman being indirectly involved.

CONCLUSIONS

Our data shows that the ribose uptake and catabolic machinery in L. sakei is highly regulated at the transcription level. A global regulation mechanism seems to permit a fine tuning of the expression of enzymes that control efficient exploitation of available carbon sources.

Metabolomics reveals alterations in both primary and secondary metabolites by wine bacteria

Lactic acid bacteria (LAB) were isolated from Korean Meoru (Vitis coigneties) wine and identified as Lactobacillus plantarum meoru0711 (KACC 91436C). The fermentative behavior and metabolic effects of L. plantarum during malolactic fermentation (MLF) were compared with those of the commercial Oenococcus oeni strain through 1H NMR- and GC-based metabolic profiling. Twenty-two primary metabolites of amino acids, carbohydrates, and organic acids, and 55 secondary metabolites of volatile compounds were identified in wines by 1H nuclear magnetic resonance (NMR) spectroscopy and gas chromatography (GC), respectively. Principal component analysis (PCA) revealed that malolactic (ML)-fermented and non-ML-fermented wines, and wines ML-fermented with O. oeni and L. plantarum were clearly differentiated. Both the primary and secondary metabolites were responsible for these differentiations. Compared to non-MLF wines, MLF wines were characterized by increased levels of primary metabolites such as lactic acid, phenylalanine, uracil, ornithine, alanine, threonine, leucine, isoleucine, and valine with decreased levels of monosaccharides, glycerol, malic, and citric acids. In addition, higher levels of secondary metabolites such as butanal, ethyl isobutylate, isobutanol, isoamyl acetate, 2-butanoate ethyl ester, isoamyl alcohol, ethyl hexanoate, glycine, acetic acid, and benzaldehyde characterized the MLF wine. Higher levels of primary metabolites such as tyrosine, monosaccharides, glycerol, alanine, 2,3-butanediol, valine, and leucine, and of secondary metabolites such as propyl acetate, isobutanol, isoamyl acetate, 1-butanol, ethyl hexanoate, prenyl alcohol, glycine, 2-hexen-1-ol, ethyl octanoate, acetic acid, benzaldehyde, and butyric, together with lower levels of lactic acid, were observed in the wines fermented by L. plantarum compared with those by O. oeni. This present study demonstrates that different genera of LAB affect both the primary and second metabolites in wine. Moreover, metabolomics with multivariate statistical analysis provide insight into wine fermentation.

Amino Acid Catabolic Pathways of Lactic Acid Bacteria

Lactic acid bacteria (LAB) constitute a diverse group of Gram positive obligately fermentative microorganisms which include both beneficial and pathogenic strains. LAB generally have complex nutritional requirements and therefore they are usually associated with nutrient-rich environments such as animal bodies, plants and foodstuffs. Amino acids represent an important resource for LAB and their utilization serves a number of physiological roles such as intracellular pH control, generation of metabolic energy or redox power, and resistance to stress. As a consequence, the regulation of amino acid catabolism involves a wide set of both general and specific regulators and shows significant differences among LAB. Moreover, due to their fermentative metabolism, LAB amino acid catabolic pathways in some cases differ significantly from those described in best studied prokaryotic model organisms such as Escherichia coli or Bacillus subtilis. Thus, LAB amino acid catabolism constitutes an interesting case for the study of metabolic pathways. Furthermore, LAB are involved in the production of a great variety of fermented products so that the products of amino acid catabolism are also relevant for the safety and the quality of fermented products.

Effect of extended aging of parma dry-cured ham on the content of oligopeptides and free amino acids

The effect of the dry-curing processing time on the release of oligopeptides and amino acids was evaluated with 158 Parma hams subdivided into three groups: (1) traditional processing (450 days); (2) extended processing (570 days); and (3) extended aging (690 days). Most of the oligopeptides and free amino acids detected increased up to the last deadline (690 days); a sharp increase of peptides below 400 Da was the main change in most aged hams. In particular, gamma-glutamyl dipeptides showed a remarkable increase during ham extended aging, acting like permanent taste-active compounds, being unsuitable for further enzymatic breakdown. The pH of fresh hams showed negative relationships (P < 0.001) with most peptides. With regard to free amino acids, the pattern was modified by different processing lengths, together with their taste categories, so that the amino acids having monosodium glutamate-like and bitter tastes were enhanced in more aged hams.

The Product of arcR, the sixth gene of the arc operon of Lactobacillus sakei, is essential for expression of the arginine deiminase pathway

Lactobacillus sakei is a lactic acid bacterium commonly used as a starter culture for dry sausage production and can utilize arginine via the arginine deiminase pathway. The arcABCTD cluster of L. sakei has been characterized, and transcriptional studies have shown that its expression is subject to carbon catabolite repression and induction by arginine. Downstream of arcD an additional gene has been found; this gene, arcR, codes for a putative regulatory protein of the Crp/Fnr family. Transcriptional studies have shown that arcR is coordinately transcribed with the remaining arc genes, and therefore, these genes constitute the arcABCTDR operon. Northern analysis also showed a complex pattern of transcripts, suggesting that processing and partial termination may play a role in regulation of the expression of individual genes of the operon. Inactivation of arcR led to arrest of transcription of the operon, indicating that the ArcR protein is essential for expression of the arc genes. The availability of this mutant made it possible to study whether the ability to utilize arginine affects the growth of L. sakei in meat fermentations. Under our experimental conditions, expression of arginine deiminase does not confer an obvious advantage to L. sakei, since the wild type and an arcR mutant strain displayed similar dynamics of growth.

Comparative survey in Lactobacillus plantarum of the growth and metabolism of arginine and citrulline in different media

Arginine deiminase activity increased in the presence of arginine in Lactobacillus plantarum strains N4 and N8 isolated from orange. The influence of citrulline and ornithine on arginine deiminase and ornithine transcarbamylase activities was strain-dependent. The growth and arginine and citrulline metabolism of L. plantarum were studied in the presence of tomato juice. Its addition enhances the growth in both strains. The specific amino acids utilization was inversely proportional to the initial glucose concentration. Arginine and citrulline addition to basal medium exerted a stimulatory effect on the growth of N4 strain, and this effect was observed only with citrulline in strain N8. The magnitude of this effect was lower in the presence of tomato juice.

Protein expression under uracil privation in Lactobacillus sakei

Lactobacillus sakei is a lactic acid bacterium belonging to the natural flora of fresh and vacuum-packed meat, and is used as the starter for manufacturing fermented sausages. This species is now being studied at the genetic level. We investigated uracil prototrophy of strain 23K in order to validate the proteomic approach to study metabolism regulations. Cells grown without uracil had lower growth rates than with uracil. Protein analysis by 2D gel electrophoresis showed that at least three polypeptides were specifically induced in the absence of uracil. Two of these polypeptides were identified as orotate phosphoribosyl transferase, catalyzing the fifth step of pyrimidine biosynthesis, and PyrR, the transcriptional regulator of the pyr operon, respectively.

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.

Relationships between arginine degradation, pH and survival in Lactobacillus sakei

Lactobacillus sakei is one of the most important lactic acid bacteria of meat and fermented meat products. It is able to degrade arginine with ammonia and ATP production by the arginine deiminase pathway (ADI). This pathway is composed of three enzymes: arginine deiminase, ornithine transcarbamoylase and carbamate kinase, and an arginine transport system. The transcription of the ADI pathway is induced by arginine and subjected to catabolite repression. In order to understand the physiological role of the degradation of this amino acid we investigated the growth of bacteria under various conditions. We show that arginine degradation is responsible for an enhanced viability during the stationary phase when cells are grown under anaerobiosis. Arginine is necessary for the induction of the ADI pathway but in association with another environmental signal. Using a mutant of the L-lactate dehydrogenase unable to lower the pH we could clearly demonstrate that (i) low pH is not responsible for cell death during the stationary phase, so survival is due to another factor than elevated pH, (ii) neither low pH nor oxygen limitation is responsible for the induction of the ADI pathway together with arginine since the ldhL mutant is able to degrade arginine under aerobiosis.

Structural and functional analysis of the gene cluster encoding the enzymes of the arginine deiminase pathway of Lactobacillus sake

Lactobacillus sake can use arginine via the arginine deiminase (ADI) pathway. We designed degenerate primers based on an alignment of known sequences of ornithine transcarbamoylase (OTC)-encoding genes in order to amplify the L. sake counterpart sequences by PCR. Screening a genomic library of L. sake in lambdaEMBL3 allowed us to isolate a clone containing a 10-kb L. sake genomic DNA insert. Sequence analysis revealed that the genes involved in arginine catabolism were clustered and encoded ADI (arcA), OTC (arcB), carbamate kinase (arcC), and a putative carrier with high similarity to the arginine/ornithine antiporter of Pseudomonas aeruginosa (arcD). Additionally, a putative transaminase-encoding gene (arcT) was located in this region. The genes followed the order arcA arcB arcC arcT arcD, which differs from that found in other microorganisms. arcA, arcB, arcC, and arcD mutants were constructed, and the ADI pathway was impaired in all of them. Transcriptional studies indicated that arcA gene is subject to catabolite repression, and under the conditions used, several transcripts could be detected, suggesting the existence of different initiation sites or processing of a larger mRNA.

Carbohydrate Utilization in Lactobacillus sake

The ability of Lactobacillus sake to use various carbon sources was investigated. For this purpose we developed a chemically defined medium allowing growth of L. sake and some related lactobacilli. This medium was used to determine growth rates on various carbohydrates and some nutritional requirements of L. sake. Mutants resistant to 2-deoxy-d-glucose (a nonmetabolizable glucose analog) were isolated. One mutant unable to grow on mannose and one mutant deficient in growth on mannose, fructose, and sucrose were studied by determining growth characteristics and carbohydrate uptake and phosphorylation rates. We show here that sucrose, fructose, mannose, N-acetylglucosamine, and glucose are transported and phosphorylated by the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS). The PTS permease specific for mannose, enzyme II(supMan), was shown to be responsible for mannose, glucose, and N-acetylglucosamine transport. A second, non-PTS system, which was responsible for glucose transport, was demonstrated. Subsequent glucose metabolism involved an ATP-dependent phosphorylation. Ribose and gluconate were transported by PTS-independent permeases.

Econutrition and health maintenance — A new concept to prevent GI inflammation, ulceration and sepsis

The nutritional needs of the gastrointestinal mucosa per se has until today been largely neglected. It is a rather novel finding, that the lower part of the digestive tract is most dependent on luminal nutrition for maintaining its integrity, structure and function. Even the most complete parenteral nutrition (PN) regimen cannot, in the absence of adequate enteral nutrition (EN), fully prevent the development of mucosal atrophy in the lower part of the digestive tract, especially the colon. Nor can PN prevent the downregulation of the colon's many important functions. Increased microbial translocation and a predisposition to sepsis are consequences of inadequate luminal nutrition. Such developments can only be prevented by oral feeding and the local 'manufacturing' of essential nutrients in the colon. Probiotic bacteria are also important, especially with respect to the function of the colonic mucosa, which is the focus of this review.

Comparison of the use of rRNA probes and conventional methods in identifying strains of Lactobacillus sake and L. curvatus isolated from meat

Published 23S rRNA directed probes for the species Lactobacillus sake and L. curvatus were used for rapid identification of lactic acid bacteria (LAB) isolated from meat. Of 96 strains of LAB from pork loin, 23 hybridised with the probe for L. sake and 16 with the probe for L. curvatus. Of 20 LAB strains from bologna, 19 strains hybridised with L. sake. By comparison with conventional biochemical tests, the probes provided a reliable identification.

Occurrence of arginine deiminase pathway enzymes in arginine catabolism by wine lactic Acid bacteria

l-Arginine, an amino acid found in significant quantities in grape juice and wine, is known to be catabolized by some wine lactic acid bacteria. The correlation between the occurrence of arginine deiminase pathway enzymes and the ability to catabolize arginine was examined in this study. The activities of the three arginine deiminase pathway enzymes, arginine deiminase, ornithine transcarbamylase, and carbamate kinase, were measured in cell extracts of 35 strains of wine lactic acid bacteria. These enzymes were present in all heterofermentative lactobacilli and most leuconostocs but were absent in all the homofermentative lactobacilli and pediococci examined. There was a good correlation among arginine degradation, formation of ammonia and citrulline, and the occurrence of arginine deiminase pathway enzymes. Urea was not detected during arginine degradation, suggesting that the catabolism of arginine did not proceed via the arginase-catalyzed reaction, as has been suggested in some earlier studies. Detection of ammonia with Nessler's reagent was shown to be a simple, rapid test to assess the ability of wine lactic acid bacteria to degrade arginine, although in media containing relatively high concentrations (>0.5%) of fructose, ammonia formation is inhibited.

Biochemical characterization of lactobacilli from dry fermented sausages

The characterization of 254 strains of lactobacilli isolated from dry spontaneously fermented sausages from 15 different producers at two different stages of ripening time is reported. The species identified were Lactobacillus sake 55%, L. curvatus 26%, L. bavaricus 11% and L. plantarum 8%. The main criteria for the identification of isolates to species level were: production of lactic acid isomers, presence of mDpm acid in cell walls, deamination of arginine and fermentation of mannitol and melibiose. The composition of the populations of lactobacilli were the same for the two stages of ripening. The deamination of arginine was tested in aerobic and anaerobic cultures and in different media by checking the production of ammonia and detecting the production of citrulline. In 94% of strains tested both methods gave identical results. In two L. sake strains arginine catabolism was dependent on culture media; for two other L. sake strains the deamination of arginine only occurred when oxygen was scarce.

A simplified key for identifying homofermentative Lactobacillus and Carnobacterium spp. from meat

Species of Lactobacillus and Carnobacterium from meat and meat products could be separated by a few biochemical characteristics; presence of meso-diaminopimelic acid in the cell wall, the isomers of lactic acid produced, production of citrulline from arginine and fermentation of some carbohydrates. This identification key was checked by DNA-DNA hybridizations studies.