Carnitine: a novel compatible solute in Lactobacillus plantarum

Biochemical and structural elucidation of the L-carnitine degradation pathway of the human pathogen Acinetobacter baumannii

Acinetobacter baumannii is an opportunistic human pathogen which can use host-derived L-carnitine as sole carbon and energy source. Recently, an L-carnitine transporter (Aci1347) and a specific monooxygense (CntA/CntB) for the intracellular cleavage of L-carnitine have been characterized. Subsequent conversion of the resulting malic semialdehyde into the central metabolite L-malate was hypothesized. Alternatively, L-carnitine degradation via D-malate with subsequent oxidation into pyruvate was proposed. Here we describe the in vitro and in vivo reconstitution of the entire pathway, starting from the as yet uncharacterized gene products of the carnitine degradation gene operon. Using recombinantly purified enzymes, enantiomer-specific formation of D-malate by the NAD(P)+-dependent malic semialdehyde dehydrogenase (MSA-DH) is demonstrated. The solved X-ray crystal structure of tetrameric MSA-DH reveals the key catalytic residues Cys290 and Glu256, accessible through opposing substrate and cofactor funnels. Specific substrate binding is enabled by Arg166, Arg284 and Ser447 while dual cofactor specificity for NAD+ and NADP+ is mediated by Asn184. The subsequent conversion of the unusual D-malate reaction product by an uncharacterized NAD+-dependent malate dehydrogenase (MDH) is shown. Tetrameric MDH is a β-decarboxylating dehydrogenase that synthesizes pyruvate. MDH experiments with alternative substrates showed a high degree of substrate specificity. Finally, the entire A. baumannni pathway was heterologously reconstituted, allowing E. coli to grow on L-carnitine as a carbon and energy source. Overall, the metabolic conversion of L-carnitine via malic semialdehyde and D-malate into pyruvate, CO2 and trimethylamine was demonstrated. Trimethylamine is also an important gut microbiota-dependent metabolite that is associated with an increased risk of cardiovascular disease. The pathway reconstitution experiments allowed us to assess the TMA forming capacity of gut microbes which is related to human cardiovascular health.

1H NMR-Based Metabolomics Profile of Green and Red Amaranthus Grown in Open Field versus Greenhouse Cultivation System

Traditionally, indigenous African leafy vegetables such as Amaranthus, blackjack, jute mallow, cleome monophyla, and spider plants have been conventionally and organically grown as weeds in open fields. However, the lack of land space due to the increase in population has resulted in unconventional, modern, and advanced agricultural farming. The introduction of a greenhouse has recently become the second most popular growing system alongside shade net and glasshouse to increase productivity and meet consumers' demand. Several studies on Amaranthus species have solely focused on physiological parameters and nutritional composition, leaving a huge gap on their metabolomic profile of the leaves which is crucial to comprehend when growing Amaranthus species in different cropping systems. Therefore, the study aimed to determine the influence of different cropping systems on the release of metabolites of two commonly consumed Amaranthus species in South Africa. H1 -Nuclear Magnetic Resonance (NMR) tool was used to profile the untargeted metabolites of green (Amaranthus graecizans L.) and red (Amaranthus cruentus L.) species. A total of 12 metabolites-trehalose, betaine, glutamine, choline, sucrose, caprate, adenosine, asparagine, carnitine, caffeine, aspartate, and alanine-were detected in green amaranth grown in open fields. Except for caffeine, aspartate, and caprate, which were found in the green amaranth grown in open fields, all the other metabolites were detected in the greenhouse grown once. Interestingly, allantoin, which serves as an allelochemical, was the sole distinct metabolite detected in greenhouse cultivated green amaranth. On the contrary, seven similar metabolites were quantified in red amaranth grown in both open fields and greenhouses, apart from caffeine, which was only detected in greenhouse-cultivated red amaranth.

Health-Promoting Nature of Lactococcus lactis IBB109 and Lactococcus lactis IBB417 Strains Exhibiting Proliferation Inhibition and Stimulation of Interleukin-18 Expression in Colorectal Cancer Cells

Lactic acid bacteria (LAB) are Gram-positive bacteria which are considered for use as adjuvant therapeutics in management of various disease ailments, including obesity, irritable bowel syndrome, lactose intolerance and cancer. To investigate the possible use of Lactococcus lactis strains from our collection in treatment of gastrointestinal cancer, we tested them for the ability to arrest proliferation of human colorectal adenocarcinoma cells (Caco-2). Results of the BrdU assay showed that the anti-proliferative activity of L. lactis cells is strain-specific. We found that particularly, two strains, L. lactis IBB109 and L. lactis IBB417, exhibited the most potent inhibitory effect. Moreover, both strains triggered interleukin 18 gene expression, normally inhibited in Caco-2 (cancer) cells. To examine the probiotic potential of the two strains, we tested them for bile salts and acid tolerance, as well as adhesion properties. Both isolates exhibited probiotic potential—they survived in the presence of 0.3% bile salts and tolerated exposure to low pH and osmotic stress. Notably, we found that L. lactis IBB417 displayed better adherence to mucus and Caco-2 cells than L. lactis IBB109. Additionally, by microdilution tests we confirmed that both strains are sensitive to all nine antibiotics of human and veterinary importance listed by the European Food Safety Authority. Finally, by in silico investigations of whole genome sequencing data, we revealed the genetic features of L. lactis IBB109 and L. lactis IBB417 that can be associated with functional (e.g., adhesion and carbohydrate metabolic genes) and safety (e.g., virulence and antibiotic resistance) aspects of the strains, confirming their health-promoting potential.

Heat-treated adzuki bean protein hydrolysates reduce obesity in mice fed a high-fat diet via remodeling gut microbiota and improving metabolic function

SCOPE

Heat-treated adzuki bean protein hydrolysates (APH) reduced cholesterol in vitro. However, it is unclear if APH have anti-obesity effects in vivo and, if so, the relationship between the effects and the improvement of gut microbiota composition and metabolic function.

METHODS AND RESULTS

Four groups of mice were fed either a normal control diet (NCD) or a high-fat diet (HFD) with or without APH for 12 weeks. In HFD-fed mice, APH supplementation significantly alleviated fat accumulation, dyslipidemia, insulin resistance, hepatic steatosis, and inflammation. In addition, APH supplementation regulated gut microbiota composition, reduced the abundance of harmful bacteria (Clostridium_sensu_stricto_1, Romboutsia, Blautia, Mucispirillum, Bilophila, and Peptococcus), enriched Lactobacillus and SCFA-producing bacteria (Lactobacillaceae, Eisenbergiella, Alistipes, Parabacteroides, Tannerellaceae, Eubacterium_nodatum_group, Acetatifactor, Rikenellaceae, and Odoribacter), and increased fecal SCFAs concentration. Importantly, APH supplementation significantly regulated the levels of serum metabolites, especially Lactobacillus-derived metabolites and tryptophan derivatives, which helped to alleviate obesity and its complications.

CONCLUSION

APH improved gut microbiota composition and metabolic function in mice and may help to prevent and treat obesity and related complications. This article is protected by copyright. All rights reserved.

Exopolysaccharide Produced by Plant-Derived Lactobacillus plantarum SN35N Exhibits Antiviral Activity

A lactic acid bacterial strain, Lactobacillus plantarum SN35N, which has been isolated from the pear, secretes negatively charged acidic exopolysaccharide (EPS) to outside cells. We have previously found that the SN35N-derived acidic EPS inhibits the catalytic activity of hyaluronidase (EC 3.2.1.35) promoting inflammation. The aim of this study is to find other health benefits of EPS. EPS has been found to exhibit an inhibitory effect against the influenza virus (Alphainfluenzavirus Influenza A virus) and feline calicivirus (Vesivirus Feline calicivirus), which is recognized as a model of norovirus. Although more studies on the structure-function relationship of EPSs are needed, SN35N-derived EPS is a promising lead for developing not only anti-inflammatory agents, but also antiviral substances.

The Exopolysaccharide Produced by Lactobacillus paracasei IJH-SONE68 Prevents and Ameliorates Inflammatory Responses in DSS-Induced Ulcerative Colitis

Inflammatory bowel disease (IBD) is an autoimmune disease characterized by chronic inflammation of the gastrointestinal tract. IBD includes Crohn’s disease (CD) and ulcerative colitis (UC). CD can occur in any part of the gastrointestinal tract, whereas UC mainly occurs in the colon and rectum. We previously demonstrated that a novel exopolysaccharide (EPS) produced by a plant-derived bacterium, Lactobacillus paracasei IJH-SONE68, prevents and improves the inflammation in contact dermatitis model mice via oral administration. To evaluate the preventive effect of the EPS against other inflammatory diseases, in the present study, we employed dextran sulfate sodium (DSS)-induced UC model mice. The stool consistency, hematochezia, and colonic atrophy of the mice were improved by the orally administered EPS. We also evaluated the cytokine transcription. Overexpression of the mouse macrophage inflammatory protein 2 mRNA in the colon as a functional homolog of human interleukin-8 was decreased by the orally administered EPS. However, the expression of interleukin-10, which is known as an anti-inflammatory cytokine, was stimulated in the EPS-administrated group. Based on these results, we conclude that the IJH-SONE68-derived EPS is a promising lead material for the development of drugs useful in treating inflammatory diseases such as UC.

Lactobacillus rhamnosus GG modifies the metabolome of pathobionts in gnotobiotic mice

Background

Lactobacillus rhamnosus GG (LGG) is the most widely used probiotic, but the mechanisms underlying its beneficial effects remain unresolved. Previous studies typically inoculated LGG in hosts with established gut microbiota, limiting the understanding of specific impacts of LGG on host due to numerous interactions among LGG, commensal microbes, and the host. There has been a scarcity of studies that used gnotobiotic animals to elucidate LGG-host interaction, in particular for gaining specific insights about how it modifies the metabolome. To evaluate whether LGG affects the metabolite output of pathobionts, we inoculated with LGG gnotobiotic mice containing Propionibacterium acnes, Turicibacter sanguinis, and Staphylococcus aureus (PTS).

Results

16S rRNA sequencing of fecal samples by Ion Torrent and MinION platforms showed colonization of germ-free mice by PTS or by PTS plus LGG (LTS). Although the body weights and feeding rates of mice remained similar between PTS and LTS groups, co-associating LGG with PTS led to a pronounced reduction in abundance of P. acnes in the gut. Addition of LGG or its secretome inhibited P. acnes growth in culture. After optimizing procedures for fecal metabolite extraction and metabolomic liquid chromatography-mass spectrometry analysis, unsupervised and supervised multivariate analyses revealed a distinct separation among fecal metabolites of PTS, LTS, and germ-free groups. Variables-important-in-projection scores showed that LGG colonization robustly diminished guanine, ornitihine, and sorbitol while significantly elevating acetylated amino acids, ribitol, indolelactic acid, and histamine. In addition, carnitine, betaine, and glutamate increased while thymidine, quinic acid and biotin were reduced in both PTS and LTS groups. Furthermore, LGG association reduced intestinal mucosal expression levels of inflammatory cytokines, such as IL-1α, IL-1β and TNF-α.

Conclusions

LGG co-association had a negative impact on colonization of P. acnes, and markedly altered the metabolic output and inflammatory response elicited by pathobionts.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02178-2.

Characterisation of antagonistic Bacillus paralicheniformis (strain EAL) by LC-MS, antimicrobial peptide genes, and ISR determinants

Plants have their own defense mechanisms such as induced systemic resistance (ISR) and systemic-acquired resistance. Bacillus spp. are familiar biocontrol agents that trigger ISR against various phytopathogens by eliciting various metabolites and producing defense enzyme in the host plant. In this study, B. paralicheniformis (strain EAL) was isolated from the medicinal plant Enicostema axillare. Butanol extract of B. paralicheniformis showed potential antagonism against Fusarium oxysporum compared to control well (sterile distilled water) A liquid chromatography mass spectrometry analysis showed 80 different compounds. Among the 80 compounds, we selected citrulline, carnitine, and indole-3-ethanol based on mass-to-charge ratio, database difference, and resolution of mass spectrum. The synthetic form of the above compounds showed biocontrol activity against F. oxysporum under in vitro condition in combination, not as individual compounds. However, the PCR amplification of 11 antimicrobial peptide genes showed that none of the genes amplified in the strain. B. paralicheniformis inoculation challenged with F. oxysporum on tomato plants enhanced production of defense enzymes such as peroxidase (POD), superoxide dismutase (SOD), phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), and proline compared to control plants (without inoculation of B. paralicheniformis) at significant level (p < 0.005). Stem of tomato plants expressed higher POD (2.2-fold), SOD (2.2-fold), PPO (1.9-fold), and PAL (1.3-fold) contents followed by the leaf and root. Elevated proline accumulation was observed in the leaf (1.8-fold) of tomato plants. Thus, results clearly showed potentiality of B. paralicheniformis (EAL) in activation of antioxidant defense enzyme against F. oxysporum-infected tomato plants and prevention of oxidative damage though hydroxyl radicals scavenging activities that suppress the occurrence of wilt diseases.

Screening of lactic starter from Tunisian fermented vegetables and application for the improvement of caper (Capparis spinosa) fermentation through an experimental factorial design

Purpose

This study aims at designing a lactic starter for caper fermentation isolated from Tunisian fermented vegetables to improve the process and produce consistent and high-quality product.

Methods

In this study, the lactic starter was isolated by exploring the lactic acid bacteria (LAB) of Tunisian artisanal fermented vegetables. Identification was carried out by partial 16S rRNA gene sequencing. Screening was based on salt tolerance and antagonistic activities against Escherichia coli ATCC 10536 and Enterococcus faecalis ATCC 10541. Caper fermentation was optimized through a full factorial experimental design (23), by exploring three factors: starter inoculum size, NaCl concentration, and acetate content. Differences in pH values, Total aerobic mesophilic bacteria and LAB counts between the beginning and end of fermentation are selected as responses and corresponding regression coefficients were calculated.

Results

The lactic microbiota is mainly represented by Lactobacillus plantarum group. Based on salt tolerance and antimicrobial activity, the strain Lactobacillus plantarum F3 was selected as starter for caper fermentation. The effect of NaCl concentration, acetate content, and inoculum size on acidity, total aerobic mesophilic bacteria count, and LAB count after 1 week and 1 month of caper fermentation was studied. Depending on the fermentation time, either 1 week or 1 month, the initial conditions should comprise 0% acetate, 108 CFU/mL inoculum, and 5% NaCl for 1 week against 5% acetate, 107 CFU/mL inoculum, and 10% NaCl for 1 month lasting caper fermentation. A protocol for caper fermentation was set up ensuring hygienic quality and LAB viability.

Conclusion

Lb. plantarum F3 was selected as lactic starter for caper fermentation, and initial fermentation conditions were optimized through a full factorial design. This work has shown loss in LAB viability after 1 week of fermentation. Based on results obtained, an optimized fermentation protocol was set up. This protocol ensures LAB survival and high hygienic quality of the product.

Exopolysaccharide Produced by Lactobacillus paracasei IJH-SONE68 Prevents and Improves the Picryl Chloride-Induced Contact Dermatitis

Allergic disease is one of the most important and common health problems worldwide. We have previously demonstrated that a fig leaf-derived lactic acid bacterium Lactobacillus (Lb.) paracasei IJH-SONE68 produces a novel exopolysaccharide (EPS). Furthermore, we have shown that the EPS inhibits the catalytic activity of hyaluronidase (EC 3.2.1.36) promoting inflammatory reactions. To evaluate the anti-allergy and anti-inflammatory effects of the EPS, in the present study, we employed the picryl-chloride-induced delayed-type (type IV) allergy model mice, which is used to evaluate the contact dermatitis. Oral administration of the EPS was observed to reduce the ear swelling in the model mice. We also observed that the overexpression of ear interleukin-4 (T helper (Th) 2 cytokine) mRNA and the increase in serum immunoglobulin E (IgE) are repressed. However, the expression of interferon-γ (Th1 cytokine) was not accelerated in all of the allergen-challenged model mice. The improvement may be responsible for the Th2 downregulation rather than the Th1 upregulation. In addition, the symptom of immediate-type (type I) allergy model mice was improved by oral administration of the IJH-SONE68 cell (data not shown). We can conclude that the IJH-SONE68-derived EPS is useful to improve the type I and IV allergies including atopic dermatitis.

Identification and characterization of a carnitine transporter in Acinetobacter baumannii

The opportunistic pathogen Acinetobacter baumannii is able to grow on carnitine. The genes encoding the pathway for carnitine degradation to the intermediate malic acid are known but the transporter mediating carnitine uptake remained to be identified. The open reading frame HMPREF0010_01347 (aci01347) of Acinetobacter baumannii is annotated as a gene encoding a potential transporter of the betaine/choline/carnitine transporter (BCCT) family. To study the physiological function of Aci01347, the gene was deleted from A. baumannii ATCC 19606. The mutant was no longer able to grow on carnitine as sole carbon and energy source demonstrating the importance of this transporter for carnitine metabolism. Aci01347 was produced in Escherichia coli MKH13, a strain devoid of any compatible solute transporter, and the recombinant E. coli MKH13 strain was found to take up carnitine in an energy-dependent fashion. Aci01347 also transported choline, a compound known to be accumulated under osmotic stress. Choline transport was osmolarity-independent which is consistent with the absence of an extended C-terminus found in osmo-activated BCCT. We propose that the Aci01347 is the carnitine transporter mediating the first step in the growth of A. baumannii on carnitine.

Characterization of the LP28 strain-specific exopolysaccharide biosynthetic gene cluster found in the whole circular genome of Pediococcus pentosaceus

We have previously isolated a lactic acid bacterium (LAB), Pediococcus pentosaceus LP28, from the longan fruit Euphoria longana. Since the plant-derived LAB strain produces an extracellular polysaccharide (EPS), in this study, we analyzed the chemical structure and the biosynthesizing genes for the EPS. The EPS, which was purified from the LP28 culture broth, was classified into acidic and neutral EPSs with a molecular mass of about 50 kDa and 40 kDa, respectively. The acidic EPS consisted of glucose, galactose, mannose, and N-acetylglucosamine moieties. Interestingly, since pyruvate residue was detected in the hydrolyzed acidic EPS, one of the four sugars may be modified with pyruvate. On the other hand, the neutral EPS consisted of glucose, mannose, and N-acetylglucosamine; pyruvate was scarcely detected in the polysaccharide molecule. As a first step to deduce the probiotic function of the EPS together with the biosynthesis, we determined the whole genome sequence of the LP28 strain, demonstrating that the genome is a circular DNA, which is composed of 1,774,865 bp (1683 ORFs) with a GC content of 37.1%. We also found that the LP28 strain harbors a plasmid carrying 6 ORFs composed of 5366 bp with a GC content of 36.5%. By comparing all of the genome sequences among the LP28 strain and four strains of P. pentosaceus reported previously, we found that 53 proteins in the LP28 strain display a similarity of less than 50% with those in the four P. pentosaceus strains. Significantly, 4 of the 53 proteins, which may be enzymes necessary for the EPS production on the LP28 strain, were absent in the other four P. pentosaceus strains and displayed less than 50% similarity with other LAB species. The EPS-biosynthetic gene cluster detected only in the LP28 genome consisted of 12 ORFs containing a priming enzyme, five glycosyltransferases, and a putative polysaccharide pyruvyltransferase.

Carnitine in bacterial physiology and metabolism

Carnitine is a quaternary amine compound found at high concentration in animal tissues, particularly muscle, and is most well studied for its contribution to fatty acid transport into mitochondria. In bacteria, carnitine is an important osmoprotectant, and can also enhance thermotolerance, cryotolerance and barotolerance. Carnitine can be transported into the cell or acquired from metabolic precursors, where it can serve directly as a compatible solute for stress protection or be metabolized through one of a few distinct pathways as a nutrient source. In this review, we summarize what is known about carnitine physiology and metabolism in bacteria. In particular, recent advances in the aerobic and anaerobic metabolic pathways as well as the use of carnitine as an electron acceptor have addressed some long-standing questions in the field.

Functional Screening of the Cronobacter sakazakii BAA-894 Genome reveals a role for ProP (ESA_02131) in carnitine uptake

Cronobacter sakazakii is a neonatal pathogen responsible for up to 80% of fatalities in infected infants. Low birth weight infants and neonates infected with C. sakazakii suffer necrotizing enterocolitis, bacteraemia and meningitis. The mode of transmission most often associated with infection is powdered infant formula (PIF) which, with an aw of ∼0.2, is too low to allow most microorganisms to persist. Survival of C. sakazakii in environments subject to extreme hyperosmotic stress has previously been attributed to the uptake of compatible solutes including proline and betaine. Herein, we report the construction and screening of a C. sakazakii genome bank and the identification of ProP (ESA_02131) as a carnitine uptake system.

Osmotic stress adaptations in rhizobacteria

Rhizobacteria have been reported to be beneficial to the plants in many different ways. Increasing salinity in the coastal agricultural zones has been shown to be a threat to the plant and microbial life in the area. Exposure of microorganisms to high-osmolality environments triggers rapid fluxes of cell water along the osmotic gradient out of the cell, thus causing a reduction in turgor and dehydration of the cytoplasm. The microorganisms have developed various adaptations to counteract the outflow of water. The first response to osmotic up shifts and the resulting efflux of cellular water is uptake of K⁺ and cells start to accumulate compatible solutes. Yet another mechanism is by altering the cell envelope composition resulting in changes in proteins, periplasmic glucans, and capsular, exo and lipopolysaccharides. Bacteria also initiate a program of gene expression in response to osmotic stress by high NaCl concentrations, which are manifested as a set of proteins produced in increased amounts in response to the stress. Genomics, transcriptomics and proteomics approaches have revealed the key components in molecular basis of bacteria salt adaptation. Understanding the mechanisms of osmo-adaptation in rhizobacteria would also be relevant from an ecological and an applicative point of view.

Two homologous Agr-like quorum-sensing systems cooperatively control adherence, cell morphology, and cell viability properties in Lactobacillus plantarum WCFS1

A two-component regulatory system of Lactobacillus plantarum, encoded by genes designated lamK and lamR (hpk10 and rrp10), was studied. The lamK and lamR genes encode proteins which are highly homologous to the quorum-sensing histidine kinase LamC and the response regulator LamA, respectively. Transcription analysis of the lamKR operon and the lamBDCA operon and liquid chromatography-mass spectrometry analysis of production of the LamD558 autoinducing peptide were performed for DeltalamA, DeltalamR, DeltalamA DeltalamR deletion mutants and a wild-type strain. The results suggested that lamA and lamR are cooperating genes. In addition, typical phenotypes of the DeltalamA mutant, such as reduced adherence to glass surfaces and filamentous cell morphology, were enhanced in the DeltalamA DeltalamR mutant. Microarray analysis suggested that the same cell wall polysaccharide synthesis genes, stress response-related genes, and cell wall protein-encoding genes were affected in the DeltalamA and DeltalamA DeltalamR mutants. However, the regulation ratio was more significant for the DeltalamA DeltalamR mutant, indicating the cooperative effect of LamA and LamR.

Siamycin attenuates fsr quorum sensing mediated by a gelatinase biosynthesis-activating pheromone in Enterococcus faecalis

The expression of two Enterococcus faecalis virulence-related proteases, gelatinase (GelE) and serine protease (SprE), is positively regulated by a quorum-sensing system encoded by the fsr gene cluster. In this system, E. faecalis secretes an autoinducing peptide, gelatinase biosynthesis-activating pheromone (GBAP), which triggers the FsrC-FsrA two-component regulatory system controlling the expression of two transcripts, fsrBDC and gelE-sprE. In the present study, we screened actinomycete metabolites for inhibitors of fsr quorum sensing. E. faecalis was cultured with each actinomycete culture supernatant tested, and the production of gelatinase and the production of GBAP were examined using the first screening and the second screening, respectively. Culture supernatant of Streptomyces sp. strain Y33-1 had the most potent inhibitory effect on both gelatinase production and GBAP production without inhibiting E. faecalis cell growth. The inhibitor in the culture supernatant was identified as a known peptide antibiotic, siamycin I. Siamycin I inhibited both gelatinase production and GBAP production at submicromolar concentrations, and it inhibited E. faecalis cell growth at concentrations above micromolar concentrations. Quantitative analysis of fsrBDC and gelE-sprE transcripts revealed that siamycin I suppressed the expression of both transcripts at a sublethal concentration. Siamycin I attenuated gelatinase production even when an overdose of GBAP was exogenously added to the culture. These results suggested that siamycin I inhibited the GBAP signaling via the FsrC-FsrA two-component regulatory system in a noncompetitive manner. The sublethal concentrations of siamycin I also attenuated biofilm formation. Treatment with siamycin could be a novel means of treating enterococcal infections.

An agr-like two-component regulatory system in Lactobacillus plantarum is involved in production of a novel cyclic peptide and regulation of adherence

We have analyzed a locus on the annotated Lactobacillus plantarum WCFS1 genome that showed homology to the staphylococcal agr quorum-sensing system and designated it lam for Lactobacillus agr-like module. Production of the lamBDCA transcript was shown to be growth phase dependent. Analysis of a response regulator-defective mutant (Delta)lamA) in an adherence assay showed that lam regulates adherence of L. plantarum to a glass surface. Global transcription analysis of the wild-type and (Delta)lamA strains in early, mid-, and late log phase of growth was performed using a clone-based microarray. Remarkably, only a small set of genes showed significant differences in transcription profiles between the wild-type and lamA mutant strains. The microarray analysis confirmed that lamBDCA is autoregulatory and showed that lamA is involved in regulation of expression of genes encoding surface polysaccharides, cell membrane proteins, and sugar utilization proteins. The lamBD genes encoding the putative autoinducing peptide precursor (LamD) and its processing protein (LamB) were overexpressed using the nisin-controlled expression system, and culture supernatants were analyzed by liquid chromatography/mass spectrometry (LC/MS) to identify overproduced LamD-derived peptides. In this way, a cyclic thiolactone pentapeptide that possesses a ring structure similar to those of autoinducing peptides of the staphylococcal agr system was identified. The peptide was designated LamD558, and its sequence (CVGIW) matched the annotated precursor peptide sequence. Time course analysis of wild-type culture supernatants by LC/MS indicated that LamD558 production was increased markedly from mid-log to late log growth phase. This is the first example of an agr-like system in nonpathogenic bacteria that encodes a cyclic thiolactone autoinducing peptide and is involved in regulation of adherence.

Potential osmoprotectants for the lactic acid bacteria Pediococcus pentosaceus and Tetragenococcus halophila

The physiological responses of the lactic acid bacteria Pediococcus pentosaceus and Tetragenococcus halophila (formely known as P. halophila), subjected to osmotic stress in the presence of molecules known to act as osmoprotectants for other bacteria were studied. In a defined medium, glycine betaine, dimethylsulfonioacetate, choline, proline and L-carnitine were able to relieve inhibition of growth at 0.8 M NaCl. The five compounds were shown to efficiently compete with glycine betaine transport, suggesting the existence of common transporter(s) for these molecules. T. halophila, the most tolerant strain, exhibited a larger spectrum of compatible solutes including dimethylsulfonioacetate, dimethylsulfoniopropionate and ectoine. Preliminary data suggest that restoration of growth by ectoine under osmotic constraint seems specific to the genus Tetragenococcus.

Heat and osmotic stress responses of probiotic Lactobacillus rhamnosus HN001 (DR20) in relation to viability after drying

The viability of lactic acid bacteria in frozen, freeze-dried, and air-dried forms is of significant commercial interest to both the dairy and food industries. In this study we observed that when prestressed with either heat (50 degrees C) or salt (0.6 M NaCl), Lactobacillus rhamnosus HN001 (also known as DR20) showed significant (P < 0.05) improvement in viability compared with the nonstressed control culture after storage at 30 degrees C in the dried form. To investigate the mechanisms underlying this stress-related viability improvement in L. rhamnosus HN001, we analyzed protein synthesis in cultures subjected to different growth stages and stress conditions, using two-dimensional gel electrophoresis and N-terminal sequencing. Several proteins were up- or down-regulated after either heat or osmotic shock treatments. Eleven proteins were positively identified, including the classical heat shock proteins GroEL and DnaK and the glycolytic enzymes glyceraldehyde-3-phosphate dehydrogenase, lactate dehydrogenase, enolase, phosphoglycerate kinase, and triose phosphate isomerase, as well as tagatose 1,6-diphosphate aldolase of the tagatose pathway. The phosphocarrier protein HPr (histidine-containing proteins) was up-regulated in cultures after the log phase irrespective of the stress treatments used. The relative synthesis of an ABC transport-related protein was also up-regulated after shock treatments. Carbohydrate analysis of cytoplasmic contents showed higher levels (20 +/- 3 microg/mg of protein) in cell extracts (CFEs) derived from osmotically stressed cells than in the unstressed control (15 +/- 3 microg/mg of protein). Liquid chromatography of these crude carbohydrate extracts showed significantly different profiles. Electrospray mass spectrometry analysis of CFEs revealed, in addition to normal mono-, di-, tri-, and tetrasaccharides, the presence of saccharides modified with glycerol.

Humectant permeability influences growth and compatible solute uptake by Staphylococcus aureus subjected to osmotic stress

The effects of different humectants (sodium chloride, sucrose, and glycerol) on the growth of and compatible solute (glycine betaine, proline, and carnitine) uptake by the osmotolerant foodborne pathogen Staphylococcus aureus were investigated. While growth in the presence of the impermeant humectants sodium chloride and sucrose induced the accumulation of proline and glycine betaine by cells, growth in the presence of the permeant humectant glycerol did not. When compatible solutes were omitted from low-water-activity media, growth was very poor in the presence of impermeant humectants. In contrast, the addition of compatible solutes had essentially no effect on growth when cells were grown in low-water-activity media containing glycerol as the humectant. Carnitine was found to accumulate to high intracellular levels in osmotically stressed cells when proline and glycine betaine were absent, making it a potentially important compatible solute for this organism.

Bacterial osmoadaptation: the role of osmolytes in bacterial stress and virulence

Two general strategies exist for the growth and survival of prokaryotes in environments of elevated osmolarity. The 'salt in cytoplasm' approach, which requires extensive structural modifications, is restricted mainly to members of the Halobacteriaceae. All other species have convergently evolved to cope with environments of elevated osmolarity by the accumulation of a restricted range of low molecular mass molecules, termed compatible solutes owing to their compatibility with cellular processes at high internal concentrations. Herein we review the molecular mechanisms governing the accumulation of these compounds, both in Gram-positive and Gram-negative bacteria, focusing specifically on the regulation of their transport/synthesis systems and the ability of these systems to sense and respond to changes in the osmolarity of the extracellular environment. Finally, we examine the current knowledge on the role of these osmostress responsive systems in contributing to the virulence potential of a number of pathogenic bacteria.

Uptake of choline from salmon flesh and its conversion to glycine betaine in response to salt stress in Shewanella putrefaciens

When cultured in M63 minimal medium plus 0.6 M NaCl, the growth of Shewanella putrefaciens was strongly inhibited. The addition of an extract from smoked salmon to this medium restored the growth almost to the unstressed level. A comparison of the 13C NMR spectra of intracellular solutes extracted from S. putrefaciens cells cultured in both conditions revealed the accumulation of glycine betaine (GB) from the smoked salmon extract (SSE). Analysis of the osmoprotective properties of this extract for several strains of Escherichia coli (which differ from each other in their ability to accumulate GB (i) from the surrounding environment, and (ii) from its hydroxylated precursor choline), demonstrated the absence of GB in the SSE. From the overall results, we inferred that salt-stressed S. putrefaciens cells accumulated GB from choline present in the SSE. Furthermore, the use of [14C]-labeled betaines gave evidence that S. putrefaciens (i) oxidised choline to GB, (ii) accumulated GB as a non-metabolisable osmolyte (up to 1300 nmol (mg dw)(-1) when cultured in a medium containing 0.5 M NaCl and either 1 mM choline or 1 mM GB), and (iii) both choline and GB uptake activities were osmotically upregulated (both activities were increased more than 50-fold in media containing 0.4 to 0.6 M NaCl). In all, our results suggest that in salted smoked salmon, S. putrefaciens imports and oxidises choline, leading to the intracellular accumulation of GB.

Glycine betaine, carnitine, and choline enhance salinity tolerance and prevent the accumulation of sodium to a level inhibiting growth of Tetragenococcus halophila

Natural-abundance (13)C-nuclear magnetic resonance was used to probe the intracellular organic solute content of the moderately halophilic bacterium Tetragenococcus halophila. When grown in complex growth media supplemented or not with NaCl, T. halophila accumulates glycine betaine and carnitine. Unlike other moderate halophiles, T. halophila was not able to produce potent osmoprotectants (such as ectoines and glycine betaine) through de novo synthesis when cultured in defined medium under hyperosmotic constraint. Addition of 2 mM carnitine, glycine betaine, or choline to defined medium improved growth parameters, not only at high salinity (up to 2.5 M NaCl) but also in media lacking NaCl. These compounds were taken up when available in the surrounding medium. The transport activity occurred at low and high salinities and seems to be constitutive. Glycine betaine and carnitine were accumulated by T. halophila in an unmodified form, while exogenously provided choline led to an intracellular accumulation of glycine betaine. This is the first evidence of the existence of a choline-glycine betaine pathway in a lactic acid bacterium. An assay showed that the compatible solutes strikingly repressed the accumulation of glutamate and slightly increased the intracellular potassium level only at high salinity. Interestingly, osmoprotectant-treated cells were able to maintain the intracellular sodium concentration at a relatively constant level (200 to 300 nmol/mg [dry weight]), independent of the NaCl concentration of the medium. In contrast, in the absence of osmoprotectant, the intracellular sodium content increased sharply from 200 to 2,060 nmol/mg (dry weight) when the salinity of the medium was raised from 1 to 2 M. Indeed, the imported compatible solutes play an actual role in regulating the intracellular Na(+) content and confer a much higher salt tolerance to T. halophila.

Involvement of manganese in conversion of phenylalanine to benzaldehyde by lactic acid bacteria

We examined the involvement of Mn(II) in the conversion of phenylalanine to benzaldehyde in cell extracts of lactic acid bacteria. Experiments performed with Lactobacillus plantarum demonstrated that Mn(II), present at high levels in this strain, is involved in benzaldehyde formation by catalyzing the conversion of phenylpyruvic acid. Experiments performed with various lactic acid bacterial strains belonging to different genera revealed that benzaldehyde formation in a strain was related to a high Mn(II) level.

Metabolism of L(-)-carnitine by Enterobacteriaceae under aerobic conditions

Different Enterobacteriaceae, such as Escherichia coli, Proteus vulgaris and Proteus mirabilis, are able to convert L(-)-carnitine, via crotonobetaine, into gamma-butyrobetaine in the presence of carbon and nitrogen sources under aerobic conditions. Intermediates of L(-)-carnitine metabolism (crotonobetaine, gamma-butyrobetaine) could be detected by thin-layer chromatography. In parallel, L(-)-carnitine dehydratase, carnitine racemasing system and crotonobetaine reductase activities were determined enzymatically. Monoclonal antibodies against purified CaiB and CaiA from E. coli O44K74 were used to screen cell-free extracts of different Enterobacteriaceae (E. coli ATCC 25922, P. vulgaris, P. mirabilis, Citrobacter freundii, Enterobacter cloacae and Klebsiella pneumoniae) grown under aerobic conditions in the presence of L(-)-carnitine.

Influence of osmolarity and the presence of an osmoprotectant on lactococcus lactis growth and bacteriocin production

Growth inhibition of Lactococcus lactis provoked by increasing osmolarity is reversed when glycine betaine (GB) or its analogs are added to a defined medium. Lacticin 481 production increased sharply with growth medium osmolarity in the absence of osmoprotectant but remained unaffected when GB was supplied in media of increasing osmolarity.

A possible role of ProP, ProU and CaiT in osmoprotection of Escherichia coli by carnitine

Exogenously provided carnitine (beta-hydroxy-L-tau-N-trimethyl aminobutyrate) was found to stimulate aerobic growth of enterohaemorrhagic Escherichia coli O157:H7 in a medium of inhibitory osmotic strength. Its osmoprotective ability is comparable with that of betaine. As carnitine is an important compound in mammalian tissues, it is suggested that it might play a role in the growth of the pathogen on low water activity (aw) meat products. Using specific uptake mutants of E. coli K-12, it was established that, under osmotic stress, carnitine accumulates in the cytoplasm following import through the ProP and ProU transport systems. Betaine and carnitine also protect E. coli cells while growing anaerobically at inhibitory osmolarity. Under these conditions, an E. coli K-12 strain with lesions in both proP and proU accumulates low levels of L-carnitine but fails to accumulate betaine when these compounds are supplied in the external medium. This is probably a result of uptake of L-carnitine by the secondary transporter CaiT. The caiT gene forms part of the caiTABCDE operon which encodes the carnitine pathway, and is transcribed during anaerobic growth in the presence of carnitine. However, further experiments revealed that the carnitine pathway, including CaiT, does not play a significant role in osmoregulation of E. coli during anaerobiosis. Together, the results indicate that ProP and ProU are the sole transport systems involved in carnitine influx, both in aerobically and anaerobically osmotically stressed E. coli cells.

Mechanism of osmotic activation of the quaternary ammonium compound transporter (QacT) of Lactobacillus plantarum

The accumulation of quaternary ammonium compounds in Lactobacillus plantarum is mediated via a single transport system with a high affinity for glycine betaine (apparent Km of 18 microM) and carnitine and a low affinity for proline (apparent Km of 950 microM) and other analogues. Mutants defective in the uptake of glycine betaine were generated by UV irradiation and selected on the basis of resistance to dehydroproline (DHP), a toxic proline analogue. Three independent DHP-resistant mutants showed reduced glycine betaine uptake rates and accumulation levels but behaved similarly to the wild type in terms of direct activation of uptake by high-osmolality conditions. Kinetic analysis of glycine betaine uptake and efflux in the wild-type and mutant cells is consistent with one uptake system for quaternary ammonium compounds in L. plantarum and a separate system(s) for their excretion. The mechanism of osmotic activation of the quaternary ammonium compound transport system (QacT) was studied. It was observed that the uptake rates were inhibited by the presence of internal substrate. Upon raising of the medium osmolality, the QacT system was rapidly activated (increase in maximal velocity) through a diminished inhibition by trans substrate as well as an effect that is independent of intracellular substrate. We also studied the effects of the cationic amphipath chlorpromazine, which inserts into the cytoplasmic membrane and thereby influences the uptake and efflux of glycine betaine. The results provide further evidence for the notion that the rapid efflux of glycine betaine upon osmotic downshock is mediated by a channel protein that is responding to membrane stretch or tension. The activation of QacT upon osmotic upshock seems to be brought about by a turgor-related parameter other than membrane stretch or tension.

Effects of temperature, salinity, and medium composition on compatible solute accumulation by thermococcus spp

The effects of salinity and growth temperature on the accumulation of intracellular organic solutes were examined by nuclear magnetic resonance spectroscopy (NMR) in Thermococcus litoralis, Thermococcus celer, Thermococcus stetteri, and Thermococcus zilligii (strain AN1). In addition, the effects of growth stage and composition of the medium were studied in T. litoralis. A novel compound identified as beta-galactopyranosyl-5-hydroxylysine was detected in T. litoralis grown on peptone-containing medium. Besides this newly discovered compound, T. litoralis accumulated mannosylglycerate, aspartate, alpha-glutamate, di-myo-inositol-1,1'(3,3')-phosphate, hydroxyproline, and trehalose. The hydroxyproline and beta-galactopyranosyl-5-hydroxylysine were probably derived from peptone, while the trehalose was derived from yeast extract; none of these three compounds was detected in the other Thermococcus strains examined. Di-myo-inositol-1,1'(3,3')-phosphate, aspartate, and mannosylglycerate were detected in T. celer and T. stetteri, and the latter organism also accumulated alpha-glutamate. The only nonmarine species studied, T. zilligii, accumulated very low levels of alpha-glutamate and aspartate. The levels of mannosylglycerate and aspartate increased in T. litoralis, T. celer, and T. stetteri in response to salt stress, while di-myo-inositol-1,1'(3,3')-phosphate was the major intracellular solute at supraoptimal growth temperatures. The phase of growth had a strong influence on the types and levels of compatible solutes in T. litoralis; mannosylglycerate and aspartate were the major solutes during exponential growth, while di-myo-inositol-1,1'(3,3')-phosphate was the predominant organic solute during the stationary phase of growth. This work revealed an unexpected ability of T. litoralis to scavenge suitable components from the medium and to use them as compatible solutes.

Influence of reduced water activity on lactose metabolism by lactococcus lactis subsp. cremoris At different pH values

The influence of reduced water activity (aw) on lactose metabolism by Lactococcus lactis subsp. cremoris 2254 and 2272 was studied at different pH values. In control incubations (aw, 0.99) with nongrowing cells in pH-controlled phosphate buffer, the levels of carbon recovered as L-(+)-lactate were 92% at pH 6.1 and 5.3 and 78% at pH 4.5. However, the levels of recovery decreased to approximately 50% at all pH values tested when the aw was 0.88 (with glycerol as the humectant). When growing cells in broth controlled at pH 6.3 were used, a reduction in the aw from 0.99 to 0.96 resulted in a decrease in the level of lactose carbon recovered as L-(+)-lactate from 100 to 71%. Low levels of L-(+)-lactate carbon recovery (<50%) were also observed with cells resuspended in pH-uncontrolled reconstituted skim milk at aw values of 0.99 and 0. 87 and in young cheese curds. The missing lactose carbon could not be accounted for by acetate, ethanol, formate, acetaldehyde, or pyruvate. Attempts were made to determine where the missing lactose carbon was diverted to under the stress conditions used. Some of the missing lactose carbon was recovered as galactose (0.1 to 2.5 mM) in culture supernatants. Decreasing either the aw or the pH resulted in increased galactose accumulation by nongrowing cells; adjusting both environmental factors together potentiated the effect. The sensitivities of the two lactococcal strains tested were different; strain 2272 was more prone to accumulate galactose under stress conditions. A methyl pentose(s) and additional galactose were found in acid-hydrolyzed supernatants from cultures containing both growing and nongrowing cells, indicating that a saccharide(s) rich in these components was formed by lactococci under low-aw and low-pH stress conditions.

Carnitine acts as a compatible solute in Brevibacterium linens

Carnitine is a trimethyl amino acid found at relatively high concentrations in materials of animal origin. Exogenously provided L-carnitine was found to stimulate growth of Brevibacterium linens ATCC 19391 in media with inhibitory osmotic strength. Its osmoprotective ability was as potent as that of glycine betaine. Electrophoretic and spectroscopic (NMR) analysis showed that this compound is only transiently accumulated, but in significant amounts, by B. linens under hyperosmotic stress and is converted into glycine betaine. The L-carnitine/glycine betaine pathway is inducible by L-carnitine in B. linens. The D-enantiomer did not improve growth of B. linens, even though this solute is accumulated by B. linens at the same level as glycine betaine. The two isomeric forms of carnitine repress the build-up of ectoine, the main endogenous osmolyte in B. linens.

Response of Bacillus subtilis to high osmolarity: uptake of carnitine, crotonobetaine and γ-butyrobetaine via the ABC transport system OpuC

Summary: It was found that low concentrations of the naturally occurring and structurally related betaines L-carnitine, crotonobetaine and γ-butyrobetaine conferred a high degree of osmotic tolerance to Bacillus subtilis. Kinetic analysis of L-[N-methyl −14C]carnitine uptake in cells grown in minimal medium revealed the presence of a high-affinity transport system with a K m value of 5 μM and a maximum rate of transport (V max) of 41 nmol min−1 (mg protein)−1. A rise in medium osmolarity moderately increased the maximum velocity [V max 71 nmol min−1 (mg protein)−1] of this transport system, but had little effect on its affinity. Growth and transport studies with a set of strains that carried defined mutations in the previously identified glycine betaine transport systems OpuA, OpuC and OpuD allowed the identification of the ATP-binding cassette (ABC) transport system OpuC as the only uptake route for L-carnitine in B. subtilis. Competition experiments with crotonobetaine and γ-butyrobetaine revealed that the OpuC system also exhibited a high affinity for these trimethylammonium compounds with K i values of 6.4 μM. Tracer experiments with radiolabelled L-carnitine and 13C-NMR tracings of cell extracts demonstrated that these betaines are accumulated by B. subtilis in an unmodified form. In contrast, the β-substituted acylcarnitine esters acetylcarnitine and octanoylcarnitine both functioned as osmoprotectants for B. subtilis but were found to be accumulated as carnitine by the cells. None of these trimethylammonium compounds were used as sole carbon or nitrogen sources. The results thus characterize L-carnitine, crotonobetaine and γ-butyrobetaine as effective compatible solutes for B. subtilis and establish a crucial role of the ABC transport system OpuC for the supply of B. subtilis with a variety of osmoprotectants.

Betaine and L-carnitine transport by Listeria monocytogenes Scott A in response to osmotic signals

The naturally occurring compatible solutes betaine and L-carnitine allow the food-borne pathogen Listeria monocytogenes to adjust to environments of high osmotic strength. Previously, it was demonstrated that L. monocytogenes possesses an ATP-dependent L-carnitine transporter (A. Verheul, F. M. Rombouts, R. R. Beumer, and T. Abee, J. Bacteriol. 177:3205-3212, 1995). The present study reveals that betaine and L-carnitine are taken up by separate highly specific transport systems and support a secondary transport mechanism for betaine uptake in L. monocytogenes. The initial uptake rates of betaine and L-carnitine are not influenced by an osmotic upshock, but the duration of transport of both osmolytes is directly related to the osmotic strength of the medium. Regulation of uptake of both betaine and L-carnitine is subject to inhibition by preaccumulated solute. Internal betaine inhibits not only transport of external betaine but also that of L-carnitine and, similarly, internal L-carnitine inhibits transport of both betaine and L-carnitine. The inhibition is alleviated upon osmotic upshock, which suggests that alterations in membrane structure are transmitted to the allosteric binding sites for betaine and L-carnitine of both transporters at the inner surface of the membrane. Upon osmotic downshock, betaine and L-carnitine are rapidly released by L. monocytogenes as a consequence of activation of a channel-like activity. The osmolyte-sensing mechanism described is new and is consistent with various unexplained observations of osmoregulation in other bacteria.

Effect of added carbohydrates on membrane phase behavior and survival of dried Lactobacillus plantarum

The relation between the protective effect of externally added carbohydrates on Lactobacillus plantarum cells during air-drying and the phase behavior of cell membranes was studied. The residual activity after drying could be improved from 44% in the control to 79 and 66% after the addition of sorbitol and maltose, respectively, whereas trehalose addition resulted in a residual activity of 30%. Membrane phase transition temperatures (Tm) were determined in intact hydrated and dry cells, using Fourier transform infrared spectroscopy. The Tm of hydrated cells was 4 degrees C, increasing to only 20 degrees C after drying. Because endogenous soluble sugars were absent, this phase behavior is attributed to the structure of the predominant phospholipids, PG and lysyl-PG. The restricted increase of Tm is held responsible for the survival of part of the cells. The added maltose, trehalose, and sorbitol did not influence Tm in vivo. We suggest that the effective carbohydrates act through their free radical scavenging activity and not by direct interaction with the polar lipid headgroups.

Mannitol, a novel bacterial compatible solute in Pseudomonas putida S12

The aim of this study was to identify the compatible solutes accumulated by Pseudomonas putida S12 subjected to osmotic stress. In response to reduced water activity, P. putida S12 accumulated Nalpha-acetylglutaminylglutamine amide (NAGGN) simultaneously with a novel compatible solute identified as mannitol (using 13C- and 1H-nuclear magnetic resonance, liquid chromatography-mass spectroscopy and high-performance liquid chromatography methods) to maximum concentrations of 74 and 258 micromol g (dry weight) of cells(-1), respectively. The intracellular amounts of each solute varied with both the type and amount of osmolyte applied to induce osmotic stress in the medium. Both solutes were synthesized de novo. Addition of betaine to the medium resulted in accumulation of this compound and depletion of both NAGGN and mannitol. Mannitol and NAGGN were accumulated when sucrose instead of salts was used to reduce the medium water activity. Furthermore, both compatible solutes were accumulated when glucose was substituted by other carbon sources. However, the intracellular quantities of mannitol decreased when fructose, succinate, or lactate were applied as a carbon source. Mannitol was also raised to high intracellular concentrations by other salt-stressed Pseudomonas putida strains. This is the first study demonstrating a principal role for the de novo-synthesized polyol mannitol in osmoadaptation of a heterotrophic eubacterium.

Effect of compatible solutes on survival of lactic Acid bacteria subjected to drying

Four strains of lactic acid bacteria were investigated to determine if a relationship exists between accumulation of compatible solutes and the ability of cells to survive drying. Betaine was the major solute found in these lactic acid bacteria subjected to salt stress. Survival of cultures subjected to drying was considerably enhanced when this solute was accumulated by cells.