Effect of hematin on the activities of nitrite reductase and catalase in lactobacilli

Nitric oxide-secreting probiotics as sustainable bio-cleaners for reverse osmosis membrane systems

Membrane biofouling in water purification plants is a serious issue of worldwide concern. Various chemical, physical, and biochemical processes are practised for membrane clean-up. A high-dosage treatment adversely affects the life expectancy of the membrane, and minimum dosage seems unable to deteriorate the biofilms on the membrane. It is reported that quorum quenchers like nitric oxide (NO) disrupt biofilm signals through metabolic rewiring, and also NO is known to be secreted by probiotics (good bacteria). In the present review, it is hypothesized that if probiotic biofilms secreting NO are used, other microbes that aggregate on the filtration membrane could be mitigated. The concept of probiotic administration on filtration membrane seeks to be encouraged because probiotic bacteria will not be hazardous, even if released during filtration. The fundamental motive to present probiotics as a resource for sequestering NO may serve as multifunctional bioweapons for membrane remediation, which will virtually guarantee their long-term sustainability and green approach.

Effect of selenium supplements on the antioxidant activity and nitrite degradation of lactic acid bacteria

Selenium (Se) is one of the essential trace elements in the human body, and Se-enriched lactic acid bacteria (LAB) can improve the biological utilization value of inorganic Se. The aim of this study was to isolate Se-enriched LAB and study their effects on antioxidant activity and nitrite degradation. The Se-enriched LAB L.P2, which was nitrite-tolerant and could grow in 30 µg/mL sodium selenite (Na₂SeO₃) medium, was isolated from the traditional fermented Chinese sauerkraut. L.P2 belonged to Lactobacillus plantarum according to the 16S rDNA analysis. The biomass and lactic acid production of L.P2 reached to a maximum (9.52 log CFU/mL and 16.99 mg/mL) when 2.0 µg/mL Na₂SeO₃ was supplemented in the medium. Additionally, the nitrite degradation rate reached 85.76% when the initial concentration of Na₂SeO₃ was 2.0 µg/mL. The Se-enriched LAB enhanced the scavenging capacity of hydroxyl radical and superoxide free radical of L.P2 and improved the lipid peroxidation and ion-chelating abilities. Moreover, the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in Se 4 group (4.0 µg/mL Na₂SeO₃ was added) reached 48.49 and 50.35 U/mg, respectively. Thus, Se 4 concentration was significantly higher than that of Se 0 group (with no Se added). In particular, SOD and GSH-Px enzymes correlated with nitrite degradation (P < 0.01). Collectively, our results indicate that Se supplementation can enhance the antioxidant capacity of LAB, contribute to its nitrite degradation, and thus may have potential applications in functional foods.

Effect of nitrate on residual nitrite decomposition rate in cooked cured pork

The effects of nitrate on the color stability of cooked cured pork were examined. Nitrate inhibited the nitrite decrement and discoloration in the cooked cured ham. Nitrate reduction and nitrite accumulation were observed in the uncooked sausage models, but were not detected in the sausage models cooked at 75°C. The kinetics of nitrite degradation was subsequently examined at various concentrations of nitric acid at constant acidity. The degradation rate of nitrite was clearly found to decrease with nitric acid content. Thus, nitrate does not appear to serve as a donor of nitrite, but rather inhibits nitrite reduction in cooked meat products, with consequent prolongation of color stability.

Investigation of reduction and tolerance capability of lactic acid bacteria isolated from kimchi against nitrate and nitrite in fermented sausage condition

Lactobacillus brevis KGR3111, Lactobacillus curvatus KGR 2103, Lactobacillus plantarum KGR 5105, and Lactobacillus sakei KGR 4108 isolated from kimchi were investigated for their potential to be used as starter culture for fermented sausages with the capability to reduce and tolerate nitrate/nitrite. The reduction capability of tested strains for nitrate was not dramatic. All tested strains, however, showed the capability to produce nitrite reductase with the reduction amount of 58.46-75.80 mg/l of NO(2)(-). L. brevis and L. plantarum showed nitrate tolerance with the highest number of 8.71 log cfu/ml and 8.81 log cfu/ml, and L. brevis and L. sakei exhibited nitrite tolerance with the highest number of 8.24 log cfu/ml and 8.25 log cfu/ml, respectively. As a result, L. brevis, L. plantarum, and L. sakei isolated from kimchi showed a tolerance against nitrate or nitrite with a good nitrite reduction capability, indicating the satisfaction of one of the selection criteria to be used as starter culture for fermented sausages.

Purification and characterization of oxygen-inducible haem catalase from oxygen-tolerant Bifidobacterium asteroides

Bifidobacterium asteroides, originally isolated from honeybee intestine, was found to grow under 20% O(2) conditions in liquid shaking culture using MRS broth. Catalase activity was detected only in cells that were exposed to O(2) and grown in medium containing a haem source, and these cells showed higher viability on exposure to H(2)O(2). Passage through multiple column chromatography steps enabled purification of the active protein, which was identified as a homologue of haem catalase on the basis of its N-terminal sequence. The enzyme is a homodimer composed of a subunit with a molecular mass of 55 kDa, and the absorption spectrum shows the typical profile of bacterial haem catalase. A gene encoding haem catalase, which has an amino acid sequence coinciding with the N-terminal amino acid sequence of the purified protein, was found in the draft genome sequence data of B. asteroides. Expression of the katA gene was induced in response to O(2) exposure. The haem catalase from B. asteroides shows about 70-80% identity with those from lactobacilli and other lactic acid bacteria, and no homologues were found in other bifidobacterial genomes.

Microbial ecology of the soppressata of Vallo di Diano, a traditional dry fermented sausage from southern Italy, and in vitro and in situ selection of autochthonous starter cultures

The microbial ecology of "soppressata of Vallo di Diano," a traditional dry fermented sausage from southern Italy, was studied by using both culture-dependent and culture-independent approaches. The ripened fermented sausages were characterized by high microbial loads of both staphylococci and lactobacilli. Using PCR-denaturing gradient gel electrophoresis (PCR-DGGE) targeting the variable V3 and V1 regions of the 16S rRNA gene and direct DNA sequencing, it was possible to identify Staphylococcus xylosus, S. succinus, and S. equorum among the staphylococci and Lactobacillus sakei and L. curvatus within the lactobacilli. Moreover, Debaryomyces hansenii was the main yeast species found by targeting the yeast 26S rRNA gene by PCR-DGGE. Selected strains of S. xylosus, L. sakei, and L. curvatus were characterized for their technological properties in the ripening conditions of the fermented sausages so as to select an autochthonous starter formulation. The selection included the determination of nitrate reductase, lipolytic, and antioxidant activity and proteolysis with myofibrillar and sarcoplasmic protein fractions. Such properties were evaluated in both in vitro and in situ assays; the latter were performed by using each strain as a starter in the laboratory-scale manufacture of soppressata of Vallo di Diano and by monitoring the microbiological and chemical changes at the end of ripening. The results show differences between the in vitro and in situ selection results and indicate that in situ evaluation of the technological performance of specific strains is better suited to selecting autochthonous starter cultures for fermented-meat products than in vitro evaluation.

Monitoring the bacterial population dynamics during fermentation of artisanal Argentinean sausages

The dynamics of the microbial community responsible for the artisanal fermentation of dry sausage produced in Argentina was investigated by using classical and molecular approaches. The combined use of RAPD analysis with primers M13, XD9, RAPD1 and RAPD2 and 16S rDNA sequencing were applied to the identification and intraspecific differentiation of 100 strains of lactobacilli and Micrococcaceae. DGGE analysis was used to monitor the dynamic changes in population after total microbial DNA was directly extracted from sausages and subjected to PCR using V3f (GC), Bact-0124f-GC and Univ-0515r primers. The sequence analysis of 16S rDNA of the dominant species was also carried out. Lactobacillus sakei and Lactobacillus plantarum were the dominant lactic acid organisms during the fermentation while Staphylococcus saprophyticus represented the dominant species of Micrococcaceae. It was demonstrated that the ripening process of Argentinean artisanal fermented sausage is driven by a limited number of Lactobacillus and Staphylococcus strains selected from environmental microbiota by the ability to best compete under the prevailing conditions of the ecological niche. The identification of dominant communities present in this artisanal fermented sausage can help in the selection of starter cultures consisting in well adapted strains to the particular production technology.

Cloning and heterologous expression of hematin-dependent catalase produced by Lactobacillus plantarum CNRZ 1228

Lactobacillus plantarum CNRZ 1228 exhibited heme-dependent catalase activity under environmental conditions similar to those encountered during sausage fermentation. The 1,455-bp catalase gene (katL) was cloned and encoded a protein of 484 amino acids. Expression of katL in a heterologous host showed that katL encodes a functional catalase. PCR screening of selected strains of lactic acid bacteria for katL indicated the presence of similar genes in other strains of lactobacilli.

Role of the dpr product in oxygen tolerance in Streptococcus mutans

We have previously identified and characterized the alkyl hydroperoxide reductase of Streptococcus mutans, which consists of two components, Nox-1 and AhpC. Deletion of both nox-1 and ahpC had no effect on the sensitivity of S. mutans to cumene hydroperoxide or H(2)O(2), implying that the existence of another antioxidant system(s) independent of the Nox-1-AhpC system compensates for the deficiency. Here, a new antioxidant gene (dpr for Dps-like peroxide resistance gene) was isolated from the S. mutans chromosome by its ability to complement an ahpCF deletion mutant of Escherichia coli with a tert-butyl hydroperoxide-hypersensitive phenotype. The dpr gene complemented the defect in peroxidase activity caused by the deletion of nox-1 and ahpC in S. mutans. Under aerobic conditions, the dpr disruption mutant carrying a spectinomycin resistance gene (dpr::Spc(r) mutant) grew as well as wild-type S. mutans in liquid medium. However, the dpr::Spc(r) mutant could not form colonies on an agar plate under air. In addition, neither the dpr::Spc(r) ahpC::Em(r)::nox-1 triple mutant nor the dpr::Spc(r) sod::Em(r) double mutant was able to grow aerobically in liquid medium. The 20-kDa dpr gene product Dpr is an iron-binding protein. Synthesis of Dpr was induced by exposure of S. mutans cells to air. We propose a mechanism by which Dpr confers aerotolerance on S. mutans.

Influence of pH, salt and nitrite on the heme-dependent catalase activity of lactic acid bacteria

A screening of commercial starter cultures used for the production of dry sausage showed a maximum heme-dependent catalase activity in the range of 60 mumol/l hematin for Lactobacillus sake, Lactobacillus plantarum, Lactobacillus pentosus and Pediococcus acidilactici. Pseudocatalase activity was not detected. In standard dry sausage production, 2-3% (w/w) nitrite salt (0.6% sodium nitrite per 100 g NaCl) is normally added, which corresponds to 4-6% salt in the water phase. In vitro experiments with L. sake and L. plantarum have shown that such a high concentration of salt caused a significant reduction of catalase activity and bacterial growth. In the case of P. acidilactici, the catalase activity remained constant at a salt concentration up to 6% (w/w); at 7% (w/w) the activity decreased sharply. The pH also affected the catalase activity, which remained constant up to pH 5.1 and decreased dramatically at lower values. The effect of nitrite has also been investigated. L. pentosus and P. acidilactici were not affected by the addition of 160 ppm nitrite (NO2-); L. plantarum, on the other hand, showed a significantly reduced catalase activity. In practice, optimum fermentation characteristics combined with an optimum catalase activity which are not inhibited by salt concentrations higher than 6% (w/v) and a residual nitrite content of about 160 ppm (w/v), are of the utmost importance in screening and selection of lactic acid bacteria for starter cultures.

Cloning, sequence, and phenotypic expression of katA, which encodes the catalase of Lactobacillus sake LTH677

Lactobacillus sake LTH677 is a strain, isolated from fermented sausage, which forms a heme-dependent catalase. This rare property is highly desirable in sausage fermentation, as it prevents rancidity and discoloration caused by hydrogen peroxide. A gene bank containing MboI fragments of chromosomal DNA from Lactobacillus sake LTH677 in Escherichia coli plasmid pBR328 was constructed. The catalase gene was cloned by heterologous complementation of the Kat- phenotype of E. coli UM2. The catalase structural gene, designated katA, was assigned to a 2.3-kb region by deletion analysis of the originally cloned fragment in plasmid pHK1000. The original chromosomal arrangement was determined by Southern hybridization. Protein analysis revealed that the catalase subunit has a molecular size of 65,000 Da and that the active catalase possesses a hexameric structure. The molecular size of the subunit deduced from the nucleotide sequence was determined to 54,504 Da. The N-terminal amino acid sequence of the 65,000-Da protein corresponded to the one deduced from the DNA sequence. After recloning of katA in the E. coli-Lactococcus shuttle vector pGKV210, the gene was successfully transferred and phenotypically expressed in Lactobacillus casei, which is naturally deficient in catalase activity.

Heme-dependent catalase activity of lactobacilli

The heme-dependent catalase in Lactobacillus pentosus, L. sake, L. delbrueckii and Enterococcus faecalis was studied. The catalase was formed by cells grown aerobically in the presence of hematin or for lactobacilli when grown without added hematin, after incubation of buffered cells in the presence of hematin. The kinetics of the production of catalase revealed maximum activity for L. pentosus and E. faecalis at late stationary and late logarithmic growth phase, respectively. The physiological role of catalase was studied with L. sake. The presence of hematin allows higher growth yields, since it protects the cells against hydrogen peroxide formed endogenously up to concentrations of 4.6 mmol/l.

Heme-dependent and heme-independent nitrite reduction by lactic acid bacteria results in different N-containing products

Seventy strains of lactic acid bacteria were investigated for nitrite reductase activity. Two types of this activity were detected. Type I was found in Lactobacillus plantarum, L. pentosus and Pediococcus pentosaceus. This activity is heme-dependent with ammonia as the sole product. Type II mechanism is heme-independent and reduces nitrite to NO and N2O.