Purification and functional characterization of a novel alpha-L-arabinofuranosidase from Bifidobacterium longum B667

Motif-guided identification of a glycoside hydrolase family 1 α-L-arabinofuranosidase in Bifidobacterium adolescentis

Members of glycoside hydrolase family 1 (GH1) cleave glycosidic linkages with a variety of physiological roles. Here we report a unique GH1 member encoded in the genome of Bifidobacterium adolescentis ATCC 15703. This enzyme, BAD0156, was identified from over 2,000 GH1 sequences accumulated in a database by a genome mining approach based on a motif sequence. A recombinant BAD0156 protein was characterized to confirm that this enzyme alone specifically hydrolyzes p-nitrophenyl-α-L-arabinofuranoside among the 24 p-nitrophenyl-glycosides examined. Among natural glycosides, α-1,5-linked arabino-oligosaccharides served as substrates, but arabinan, debranched arabinan, arabinoxylan, and arabinogalactan did not. A time course analysis of arabino-oligosaccharide hydrolysis indicated that BAD0156 is an exo-acting enzyme. These results suggest that BAD0156 is an α-L-arabinofuranosidase. This is the first report of a GH1 enzyme that acts specifically on arabinosides, providing information on GH1 substrate specificity.

Purification and characterization of β-D-xylosidase from Lactobacillus brevis grown on xylo-oligosaccharides

In the recent years there has been a growing interest in the use of oligosaccharides as prebiotics to modulate gut microbiota with an aim to improve the gut health. Though xylo-oligosaccharides (XOS) have been increasingly used as prebiotics, information pertaining to the enzymes used by lactobacilli to degrade these substrates is scanty. Present investigation reports the purification and characterization of β-D-xylosidase from Lactobacillus brevis NCDC01 grown on XOS. Three sequential steps consisting of ultra-filtration, DEAE cellulose ion-exchange and Sephacryl S-100 gel filtration chromatographies were employed to purify the enzyme to apparent homogeneity and it was found to be monomeric on SDS-PAGE with an apparent molecular mass of ~58.0 kDa. The pH and temperature optima were 6.0 and 40 °C respectively. The enzyme remained stable over a pH range of 5.5-7.5 and up to 50 °C for 30 min. Under optimum pH and temperature with p-nitrophenyl β-D-xylopyranoside as a substrate, the enzyme exhibited a K(m) of 0.87 mM. The enzyme does not require any metal ion for activity or stability but is completely inhibited by Hg(2+), Pb(2+), p-chloromercuribenzoate (PCMB), oxalic acid and citric acid. This is perhaps the first report on the purification and characterization of β-D-xylosidase from Lactobacillus brevis NCDC01.

Role of extracellular transaldolase from Bifidobacterium bifidum in mucin adhesion and aggregation

The ability of bifidobacteria to establish in the intestine of mammals is among the main factors considered to be important for achieving probiotic effects. The role of surface molecules from Bifidobacterium bifidum taxon in mucin adhesion capability and the aggregation phenotype of this bacterial species was analyzed. Adhesion to the human intestinal cell line HT29 was determined for a collection of 12 B. bifidum strains. In four of them-B. bifidum LMG13195, DSM20456, DSM20239, and A8-the involvement of surface-exposed macromolecules in the aggregation phenomenon was determined. The aggregation of B. bifidum A8 and DSM20456 was abolished after treatment with proteinase K, this effect being more pronounced for the strain A8. Furthermore, a mucin binding assay of B. bifidum A8 surface proteins showed a high adhesive capability for its transaldolase (Tal). The localization of this enzyme on the surface of B. bifidum A8 was unequivocally demonstrated by immunogold electron microscopy experiments. The gene encoding Tal from B. bifidum A8 was expressed in Lactococcus lactis, and the protein was purified to homogeneity. The pure protein was able to restore the autoaggregation phenotype of proteinase K-treated B. bifidum A8 cells. A recombinant L. lactis strain, engineered to secrete Tal, displayed a mucin- binding level more than three times higher than the strain not producing the transaldolase. These findings suggest that Tal, when exposed on the cell surface of B. bifidum, could act as an important colonization factor favoring its establishment in the gut.

A bile-inducible membrane protein mediates bifidobacterial bile resistance

Bbr_0838 from Bifidobacterium breve UCC2003 is predicted to encode a 683 residue membrane protein, containing both a permease domain that displays similarity to transporters belonging to the major facilitator superfamily, as well as a CBS (cystathionine beta synthase) domain. The high level of similarity to bile efflux pumps from other bifidobacteria suggests a significant and general role for Bbr_0838 in bile tolerance. Bbr_0838 transcription was shown to be monocistronic and strongly induced upon exposure to bile. Further analysis delineated the transcriptional start site and the minimal region required for promoter activity and bile regulation. Insertional inactivation of Bbr_0838 in B. breve UCC2003 resulted in a strain, UCC2003:838₈₀₀, which exhibited reduced survival upon cholate exposure as compared with the parent strain, a phenotype that was reversed when a functional, plasmid‐encoded Bbr_0838 gene was introduced into UCC2003:838₈₀₀. Transcriptome analysis of UCC2003:838₈₀₀ grown in the presence or absence of bile demonstrated that transcription of Bbr_0832, which is predicted to encode a macrolide efflux transporter gene, was significantly increased in the presence of bile, representing a likely compensatory mechanism for bile removal in the absence of Bbr_0838. This study represents the first in‐depth analysis of a bile‐inducible locus in bifidobacteria, identifying a key gene relevant for bifidobacterial bile tolerance.

Discovering novel bile protection systems in Bifidobacterium breve UCC2003 through functional genomics

Tolerance of gut commensals to bile salt exposure is an important feature for their survival in and colonization of the intestinal environment. A transcriptomic approach was employed to study the response of Bifidobacterium breve UCC2003 to bile, allowing the identification of a number of bile-induced genes with a range of predicted functions. The potential roles of a selection of these bile-inducible genes in bile protection were analyzed following heterologous expression in Lactococcus lactis. Genes encoding three transport systems belonging to the major facilitator superfamily (MFS), Bbr_0838, Bbr_0832, and Bbr_1756, and three ABC-type transporters, Bbr_0406-0407, Bbr_1804-1805, and Bbr_1826-1827, were thus investigated and shown to provide enhanced resistance and survival to bile exposure. This work significantly improves our understanding as to how bifidobacteria respond to and survive bile exposure.

Controlled gene expression in bifidobacteria by use of a bile-responsive element

The promoter activity of the upstream region of the bile-inducible gene betA from Bifidobacterium longum subsp. longum NCC2705 was characterized. DNA fragments were cloned into the reporter vector pMDYAbfB, and the arabinofuranosidase activity was determined under different in vitro conditions. A segment of 469 bp was found to be the smallest operational unit that retains bile inducibility. The reporter activity was strongly affected by the presence of ox gall, cholate, and conjugated cholate, but not by other bile salts and cell-surface-acting compounds. Remarkably, this bile-inducible system was also active in other bifidobacteria containing betA homologs.

Carbohydrate metabolism in Bifidobacteria

Members of the genus Bifidobacterium can be found as components of the gastrointestinal microbiota, and are believed to play an important role in maintaining and promoting human health by eliciting a number of beneficial properties. Bifidobacteria can utilize a diverse range of dietary carbohydrates that escape degradation in the upper parts of the intestine, many of which are plant-derived oligo- and polysaccharides. The gene content of a bifidobacterial genome reflects this apparent metabolic adaptation to a complex carbohydrate-rich gastrointestinal tract environment as it encodes a large number of predicted carbohydrate-modifying enzymes. Different bifidobacterial strains may possess different carbohydrate utilizing abilities, as established by a number of studies reviewed here. Carbohydrate-degrading activities described for bifidobacteria and their relevance to the deliberate enhancement of number and/or activity of bifidobacteria in the gut are also discussed in this review.

Substrate specificity of three recombinant α-L-arabinofuranosidases from Bifidobacterium adolescentis and their divergent action on arabinoxylan and arabinoxylan oligosaccharides

Bifidobacterium adolescentis possesses several arabinofuranosidases able to hydrolyze arabinoxylans (AX) and AX oligosaccharides (AXOS), the latter being bifidogenic carbohydrates with potential prebiotic properties. We characterized two new recombinant arabinofuranosidases, AbfA and AbfB, and AXH-d3, a previously studied arabinofuranosidase from B. adolescentis. AbfA belongs to glycoside hydrolase family (GH) 43 and removed arabinose from the C(O)2 and C(O)3 position of monosubstituted xylose residues. Furthermore, hydrolytic activity of AbfA was much larger towards substrates with a low amount of arabinose substitutions. AbfB from GH 51 only cleaved arabinoses on position C(O)3 of disubstituted xyloses, similar to GH 43 AXH-d3, making it to our knowledge, the first reported enzyme with this specificity in GH 51. AbfA acted synergistically with AbfB and AXH-d3. In combination with AXH-d3, it released 60% of arabinose from wheat AX. Together with recent studies on other AXOS degrading enzymes from B. adolescentis, these findings allowed us to postulate a mechanism for the uptake and hydrolysis of bifidogenic AXOS by this organism.

Identification and characterization of a novel Terrabacter ginsenosidimutans sp. nov. beta-glucosidase that transforms ginsenoside Rb1 into the rare gypenosides XVII and LXXV

A new beta-glucosidase from a novel strain of Terrabacter ginsenosidimutans (Gsoil 3082(T)) obtained from the soil of a ginseng farm was characterized, and the gene, bgpA (1,947 bp), was cloned in Escherichia coli. The enzyme catalyzed the conversion of ginsenoside Rb1 {3-O-[beta-D-glucopyranosyl-(1-2)-beta-D-glucopyranosyl]-20-O-[beta-D-glucopyranosyl-(1-6)-beta-D-glucopyranosyl]-20(S)-protopanaxadiol} to the more pharmacologically active rare ginsenosides gypenoside XVII {3-O-beta-D-glucopyranosyl-20-O-[beta-D-glucopyranosyl-(1-6)-beta-D-glucopyranosyl]-20(S)-protopanaxadiol}, gypenoside LXXV {20-O-[beta-v-glucopyranosyl-(1-6)-beta-D-glucopyranosyl]-20(S)-protopanaxadiol}, and C-K [20-O-(beta-D-glucopyranosyl)-20(S)-protopanaxadiol]. A BLAST search of the bgpA sequence revealed significant homology to family 3 glycoside hydrolases. Expressed in E. coli, beta-glucosidase had apparent K(m) values of 4.2 +/- 0.8 and 0.14 +/- 0.05 mM and V(max) values of 100.6 +/- 17.1 and 329 +/- 31 micromol x min(-1) x mg of protein(-1) against p-nitrophenyl-beta-D-glucopyranoside and Rb1, respectively. The enzyme catalyzed the hydrolysis of the two glucose moieties attached to the C-3 position of ginsenoside Rb1, and the outer glucose attached to the C-20 position at pH 7.0 and 37 degrees C. These cleavages occurred in a defined order, with the outer glucose of C-3 cleaved first, followed by the inner glucose of C-3, and finally the outer glucose of C-20. These results indicated that BgpA selectively and sequentially converts ginsenoside Rb1 to the rare ginsenosides gypenoside XVII, gypenoside LXXV, and then C-K. Herein is the first report of the cloning and characterization of a novel ginsenoside-transforming beta-glucosidase of the glycoside hydrolase family 3.

Production of human growth hormone by Lactococcus lactis

A synthetic gene coding for human growth hormone was expressed in Lactococcus lactis. The presence of the recombinant protein was assayed and quantified using ELISA tests. Human growth hormone was detected at high concentrations and displayed a biological activity similar to the one shown by commercial human growth hormone.

alpha-L-Arabinofuranosidase from Streptomyces sp. PC22: purification, characterization and its synergistic action with xylanolytic enzymes in the degradation of xylan and agricultural residues

alpha-l-Arabinofuranosidase was purified from culture filtrates of the thermoalkaliphilic Streptomyces sp. PC22 to about 108-fold purity by (NH(4))(2)SO(4) precipitation followed by column chromatography. Its approximate molecular weight was 404kDa, with a subunit mass of approximately 79kDa. The evaluated K(m) and V(max) values with p-nitrophenyl-alpha-l-arabinofuranoside as substrate were 0.23mM and 124 U.mg(-1), respectively. The purified enzyme was optimally active at 65 degrees C and pH 6.0 and showed a mild but significant synergistic effect in combination with other xylanolytic enzymes, including xylanase, beta-xylosidase and acetyl esterase, on the degradation of oat-spelt xylan, corn cob and corn husk substrates with a 1.25, 1.32 and 1.21-fold increase in the amount of reducing sugar released, respectively, compared to the expected (additive) amounts for the individual enzymes acting alone. Sequential reactions using two xylan-backbone degrading enzymes (xylanase/beta-xylosidase) and two debranching enzymes (alpha-l-arabinofuranosidase/acetyl esterase) were also determined. The highest degree of synergy was obtained in sequential reactions with the debranching enzyme digestion preceding the xylan-backbone degrading enzymes.

Improved cloning vectors for bifidobacteria, based on the Bifidobacterium catenulatum pBC1 replicon

This study reports the development of several cloning vectors for bifidobacteria based on the replicon of pBC1, a cryptic plasmid from Bifidobacterium catenulatum L48 thought to replicate via the theta mode. These vectors, in which antibiotic resistance genes encoding either erythromycin or tetracycline resistance acted as selection markers, were able to replicate in a series of eight Bifidobacterium species at frequencies ranging from 4.0 x 10(1) to 1.0 x 10(5) transformants microg(-1) but not in Lactococcus lactis or Lactobacillus casei. They showed a relative copy number of around 30 molecules per chromosome equivalent and a good segregational stability, with more than 95% of the cells retaining the vectors after 80 to 100 generations in the absence of selection. Vectors contain multiple cloning sites of different lengths, and the lacZalpha peptide gene was introduced into one of the molecules, thus allowing the easy selection of colonies harboring recombinant plasmids in Escherichia coli. The functionality of the vectors for engineering Bifidobacterium strains was assessed by cloning and examining the expression of an alpha-l-arabinofuranosidase gene belonging to Bifidobacterium longum. E. coli and Bifidobacterium pseudocatenulatum recombinant clones were stable and showed an increase in alpha-arabinofuranosidase activity of over 100-fold compared to that of the untransformed hosts.

Bifidobacterium carbohydrases-their role in breakdown and synthesis of (potential) prebiotics

There is an increasing interest to positively influence the human intestinal microbiota through the diet by the use of prebiotics and/or probiotics. It is anticipated that this will balance the microbial composition in the gastrointestinal tract in favor of health promoting genera such as Bifidobacterium and Lactobacillus. Carbohydrates like non-digestible oligosaccharides are potential prebiotics. To understand how these bacteria can grow on these carbon sources, knowledge of the carbohydrate-modifying enzymes is needed. Little is known about the carbohydrate-modifying enzymes of bifidobacteria. The genome sequence of Bifidobacterium adolescentis and Bifidobacterium longum biotype longum has been completed and it was observed that for B. longum biotype longum more than 8% of the annotated genes were involved in carbohydrate metabolism. In addition more sequence data of individual carbohydrases from other Bifidobacterium spp. became available. Besides the degradation of (potential) prebiotics by bifidobacterial glycoside hydrolases, we will focus in this review on the possibilities to produce new classes of non-digestible oligosaccharides by showing the presence and (transglycosylation) activity of the most important carbohydrate modifying enzymes in bifidobacteria. Approaches to use and improve carbohydrate-modifying enzymes in prebiotic design will be discussed.

Two membrane proteins from Bifidobacterium breve UCC2003 constitute an ABC-type multidrug transporter

Intrinsic resistance to drugs is one of the main determining factors in bacterial survival in the intestinal ecosystem. This is mediated by, among others, multidrug resistance (MDR) transporters, membrane proteins which extrude noxious compounds with very different chemical structures and cellular targets. Two genes from Bifidobacterium breve encoding hypothetical membrane proteins with a high homology with members of the ATP-binding cassette (ABC) family of multidrug efflux transporters, were expressed separately and jointly in Lactococcus lactis. Cells co-expressing both proteins exhibited enhanced resistance levels to the antimicrobials nisin and polymyxin B. Furthermore, the drug extrusion activity in membrane vesicles was increased when both proteins were co-expressed, compared to membranes in which the proteins were produced independently. Both proteins were co-purified from the membrane as a stable complex in a 1:1 ratio. This is believed to be the first study of a functional ABC-type multidrug transporter in Bifidobacterium and contributes to our understanding of the molecular mechanisms underlying the capacity of intestinal bacteria to tolerate cytotoxic compounds.

Purification and characterization of a highly thermostable α-l-Arabinofuranosidase from Geobacillus caldoxylolyticus TK4

The gene encoding an alpha-L: -arabinofuranosidase from Geobacillus caldoxylolyticus TK4, AbfATK4, was isolated, cloned, and sequenced. The deduced protein had a molecular mass of about 58 kDa, and analysis of its amino acid sequence revealed significant homology and conservation of different catalytic residues with alpha-L: -arabinofuranosidases belonging to family 51 of the glycoside hydrolases. A histidine tag was introduced at the N-terminal end of AbfATK4, and the recombinant protein was expressed in Escherichia coli BL21, under control of isopropyl-beta-D-thiogalactopyranoside-inducible T7 promoter. The enzyme was purified by nickel affinity chromatography. The molecular mass of the native protein, as determined by gel filtration, was about 236 kDa, suggesting a homotetrameric structure. AbfATK4 was active at a broad pH range (pH 5.0-10.0) and at a broad temperature range (40-85 degrees C), and it had an optimum pH of 6.0 and an optimum temperature of 75-80 degrees C. The enzyme was more thermostable than previously described arabinofuranosidases and did not lose any activity after 48 h incubation at 70 degrees C. The protein exhibited a high level of activity with p-nitrophenyl-alpha-L: -arabinofuranoside, with apparent K (m) and V (max) values of 0.17 mM and 588.2 U/mg, respectively. AbfATK4 also exhibited a low level of activity with p-nitrophenyl-beta-D: -xylopyranoside, with apparent K (m) and V (max) values of 1.57 mM and 151.5 U/mg, respectively. AbfATK4 released L: -arabinose only from arabinan and arabinooligosaccharides. No endoarabinanase activity was detected. These findings suggest that AbfATK4 is an exo-acting enzyme.

Induction of alpha-L-arabinofuranosidase activity by monomeric carbohydrates in Bifidobacterium longum and ubiquity of encoding genes

Bifidobacterium longum can be isolated from human faeces, some strains being considered probiotics. B. longum NIZO B667 produces an exo-acting alpha-L-arabinofuranosidase, AbfB, previously purified by us, that releases L-arabinose from arabinan and arabinoxylan. This activity was subjected to two-seven-fold induction by L-arabinose, D-xylose, L-arabitol and xylitol and to repression by glucose. Maximum activity was obtained at 48 h incubation except for D-xylose that was at 24 h. High concentrations (200 mM) of L-arabitol also caused repression of the arabinofuranosidase. A unique band of activity showing the same migration pattern as the purified AbfB was found in zymograms of cell free extracts, indicating that the activity was likely due to this sole enzyme. The assessment of the influence of inducers and repressors on the activity of AbfB and on the expression of the abfB gene by real time PCR indicated that regulation was transcriptional. DNA amplifications using a pair of degenerated primers flanking an internal fragment within alpha-L-arabinofuranosidase genes of the family 51 of glycoside hydrolases evidenced that these enzymes are widespread in Bifidobacterium. The aminoacidic sequences of bifidobacteria included a fragment of four to six residues in the position 136-141 that was absent in other microorganisms.

Substrate preference of Bifidobacterium adolescentis MB 239: compared growth on single and mixed carbohydrates

The utilization of mono-, di-, and oligosaccharides by Bifidobacterium adolescentis MB 239 was investigated. Raffinose, fructooligosaccharides (FOS), lactose, and the monomeric moieties glucose and fructose were used. To establish a hierarchy of sugars preference, the kinetics of growth and sugar consumption were determined on individual and mixed carbohydrates. On single carbon sources, higher specific growth rates and cell yields were attained on di- and oligosaccharides compared to monosaccharides. Analysis of the carbohydrates in steady-state chemostat cultures, growing at the same dilution rate on FOS, lactose, or raffinose, showed that monomeric units and hydrolysis products were present. In chemostat cultures on individual carbohydrates, B. adolescentis MB 239 simultaneously displayed alpha-galactosidase, beta-galactosidase, and beta-fructofuranosidase activities on all the sugars, including monosaccharides. Glycosyl hydrolytic activities were found in cytosol, cell surface, and growth medium. Batch experiments on mixtures of carbohydrates showed that they were co-metabolized by B. adolescentis MB 239, even if different disappearance kinetics were registered. When mono-, di-, and oligosaccharides were simultaneously present in the medium, no precedence for monosaccharides utilization was observed, and di- and oligosaccharides were consumed before their constitutive moieties.

A proteome reference map and proteomic analysis of Bifidobacterium longum NCC2705

A comprehensive proteomic study was carried out to identify and characterize proteins expressed by Bifidobacterium longum NCC2705. A total of 708 spots representing 369 protein entries were identified by MALDI-TOF-MS and/or ESI-MS/MS. Isoelectric point values estimated by gel electrophoresis matched closely with their predicted ones, although some discrepancies exist suggesting that post-translational protein modifications might be common in B. longum. The identified proteins represent 21.4% of the predicted 1727 ORFs in the genome and correspond to 30% of the predicted proteome. Moreover 95 hypothetical proteins were experimentally identified. This is the first compilation of a proteomic reference map for the important probiotic organism B. longum NCC2705. The study aimed to define a number of cellular pathways related to important physiological processes at the proteomic level. Proteomic comparison of glucose- and fructose-grown cells revealed that fructose and glucose are catabolized via the same degradation pathway. Interestingly the sugar-binding protein specific to fructose (BL0033) and Frk showed higher levels of expression in cells grown on fructose than on glucose as determined by semiquantitative RT-PCR. BL0033 time course and concentration experiments showed that the induction time and fructose concentration correlates to increased expression of BL0033. At the same time, an ABC (ATP-binding cassette) transporter ATP-binding protein (BL0034) was slightly up-regulated in cells grown on fructose compared with glucose. All of the above results suggest that the uptake of fructose into the cell may be conducted by a specific transport system in which BL0033 might play an important role.

Macrolide resistance mediated by a Bifidobacterium breve membrane protein

A gene coding for a hypothetical membrane protein from Bifidobacterium breve was expressed in Lactococcus lactis. Immunoblotting demonstrated that this protein is located in the membrane. Phenotypical changes in sensitivity towards 21 antibiotics were determined. The membrane protein-expressing cells showed higher levels of resistance to several macrolides.

Alpha-L-arabinofuranosidases: the potential applications in biotechnology

Recently, alpha-L-arabinofuranosidases (EC3.2.1.55) have received increased attention primarily due to their role in the degradation of lignocelluloses as well as their positive effect on the activity of other enzymes acting on lignocelluloses. As a result, these enzymes are used in many biotechnological applications including wine industry, clarification of fruit juices, digestion enhancement of animal feedstuffs and as a natural improver for bread. Moreover, these enzymes could be used to improve existing technologies and to develop new technologies. The production, mechanisms of action, classification, synergistic role, biochemical properties, substrate specificities, molecular biology and biotechnological applications of these enzymes have been reviewed in this article.

Enzymatic ability of Bifidobacterium animalis subsp. lactis to hydrolyze milk proteins: identification and characterization of endopeptidase O

The proteolytic system of Bifidobacterium animalis subsp. lactis was analyzed, and an intracellular endopeptidase (PepO) was identified and characterized. This work reports the first complete cloning, purification, and characterization of a proteolytic enzyme in Bifidobacterium spp. Aminopeptidase activities (general aminopeptidases, proline iminopeptidase, X-prolyl dipeptidylaminopeptidase) found in cell extracts of B. animalis subsp. lactis were higher for cells that had been grown in a milk-based medium than for those grown in MRS. A high specific proline iminopeptidase activity was observed in B. animalis subsp. lactis. Whole cells and cell wall-bound protein fractions showed no caseinolytic activity; however, the combined action of intracellular proteolytic enzymes could hydrolyze casein fractions rapidly. The endopeptidase activity of B. animalis subsp. lactis was examined in more detail, and the gene encoding an endopeptidase O in B. animalis subsp. lactis was cloned and overexpressed in Escherichia coli. The deduced amino acid sequence for B. animalis subsp. lactis PepO indicated that it is a member of the M13 peptidase family of zinc metallopeptidases and displays 67.4% sequence homology with the predicted PepO protein from Bifidobacterium longum. The recombinant enzyme was shown to be a 74-kDa monomer. Activity of B. animalis subsp. lactis PepO was found with oligopeptide substrates of at least 5 amino acid residues, such as met-enkephalin, and with larger substrates, such as the 23-amino-acid peptide alpha s1-casein(f1-23). The predominant peptide bond cleaved by B. animalis subsp. lactis PepO was on the N-terminal side of phenylalanine residues. The enzyme also showed a post-proline secondary cleavage site.

Phytase activity as a novel metabolic feature inBifidobacterium

Phytase activity has been detected for the first time in Bifidobacterium spp. These bacteria were able to dephosphorylate phytic acid (myo-inositol hexaphosphate, IP(6)) and generate several myo-inositol phosphate intermediates (IP(3)-IP(5)). B. globosum and B. pseudocatenulatum were optimally active at neutral-alkaline pH and B. adolescentis, B. angulatum and B. longum at acid pH. B. pseudocatenulatum showed the highest levels of phytase activity. This species produced maximum activity in the exponential phase of growth and when fructo-oligosaccharides were used as carbon source in the culture medium. The potential role of phytase activity from Bifidobacterium spp. in the reduction of the antinutritional properties of IP(6) is discussed.

Cloning and characterization of arabinoxylan arabinofuranohydrolase-D3 (AXHd3) from Bifidobacterium adolescentis DSM20083

Arabinoxylan arabinofuranohydrolase-D3 (AXHd3) from Bifidobacterium adolescentis releases only C3-linked arabinose residues from double-substituted xylose residues. A genomic library of B. adolescentis DSM20083 was screened for the presence of the axhD3 gene. Two plasmids were identified containing part of the axhD3 gene. The nucleotide sequences were combined and three open reading frames (ORFs) were found. The first ORF showed high homology with xylanases belonging to family 8 of the glycoside hydrolases and this gene was designated xylA. The second ORF was the axhD3 gene belonging to glycoside hydrolase family 43. The third (partial) ORF coded for a putative carboxylesterase. The axhD3 gene was cloned and expressed in Escherichia coli. Several substrates were employed in the biochemical characterization of recombinant AXHd3. The enzyme showed the highest activity toward wheat arabinoxylan oligosaccharides. In addition, beta-xylanase from Trichoderma sp. was able to degrade soluble wheat arabinoxylan polymer to a higher extent, after pretreatment with recombinant AXHd3. Arabinoxylan oligosaccharides incubated with a combination of recombinant AXHd3 and an alpha-L-arabinofuranosidase from Aspergillus niger did not result in a higher maximal release of arabinose than incubation with these enzymes separately.

Bifidobacterium longum requires a fructokinase (Frk; ATP:D-fructose 6-phosphotransferase, EC 2.7.1.4) for fructose catabolism

Although the ability of Bifidobacterium spp. to grow on fructose as a unique carbon source has been demonstrated, the enzyme(s) needed to incorporate fructose into a catabolic pathway has hitherto not been defined. This work demonstrates that intracellular fructose is metabolized via the fructose-6-P phosphoketolase pathway and suggests that a fructokinase (Frk; EC 2.7.1.4) is the enzyme that is necessary and sufficient for the assimilation of fructose into this catabolic route in Bifidobacterium longum. The B. longum A10C fructokinase-encoding gene (frk) was expressed in Escherichia coli from a pET28 vector with an attached N-terminal histidine tag. The expressed enzyme was purified by affinity chromatography on a Co(2+)-based column, and the pH and temperature optima were determined. A biochemical analysis revealed that Frk displays the same affinity for fructose and ATP (Km(fructose) = 0.739 +/- 0.18 mM and Km(ATP) = 0.756 +/- 0.08 mM), is highly specific for D-fructose, and is inhibited by an excess of ATP (>12 mM). It was also found that frk is inducible by fructose and is subject to glucose-mediated repression. Consequently, this work presents the first characterization at the molecular and biochemical level of a fructokinase from a gram-positive bacterium that is highly specific for D-fructose.