Extracellular beta-galactosidase activity of a Fibrobacter succinogenes S85 mutant able to catabolize lactose

Fibrobacter succinogenes S85 is unable to grow with lactose as the source of carbohydrate, although it does exhibit low beta-galactosidase (EC 3.2.1.23) activity. Spontaneous mutants of strain S85 able to grow on lactose were isolated after spreading cells on a chemically defined agar medium with lactose as the carbohydrate source. A lactose-catabolizing isolate, designated L2, exhibited a sodium dodecyl sulfate-polyacrylamide gel electrophoresis protein profile and an immunoblot profile with polyclonal antibodies to whole cells of S85 which were identical to those observed for S85. Strain L2 exhibited both cell-associated and extracellular beta-galactosidase activity with either p-nitrophenyl-beta-D-galactopyranoside or lactose as the substrate. The cell-associated enzyme exhibited the greatest activity in the periplasmic space. Enzyme production was partially inhibited by glucose. The beta-galactosidase was activated by divalent cations and exhibited a pH optimum of 6.5. Analysis of the extracellular culture fluid revealed that glucose derived from the hydrolysis of lactose was used for growth, but galactose was not metabolized further. Cells were unable to take up the lactose analog, methyl-beta-D-thiogalactopyranoside. These data suggest that beta-galactosidase of F. succinogenes L2 cleaves lactose outside the cells and that the glucose released is catabolized while the galactose accumulates in the extracellular culture fluid.     

Extracellular beta-galactosidase activity of a Fibrobacter succinogenes S85 mutant able to catabolize lactose.

Fibrobacter succinogenes S85 is unable to grow with lactose as the source of carbohydrate, although it does exhibit low beta-galactosidase (EC 3.2.1.23) activity. Spontaneous mutants of strain S85 able to grow on lactose were isolated after spreading cells on a chemically defined agar medium with lactose as the carbohydrate source. A lactose-catabolizing isolate, designated L2, exhibited a sodium dodecyl sulfate-polyacrylamide gel electrophoresis protein profile and an immunoblot profile with polyclonal antibodies to whole cells of S85 which were identical to those observed for S85. Strain L2 exhibited both cell-associated and extracellular beta-galactosidase activity with either p-nitrophenyl-beta-D-galactopyranoside or lactose as the substrate. The cell-associated enzyme exhibited the greatest activity in the periplasmic space. Enzyme production was partially inhibited by glucose. The beta-galactosidase was activated by divalent cations and exhibited a pH optimum of 6.5. Analysis of the extracellular culture fluid revealed that glucose derived from the hydrolysis of lactose was used for growth, but galactose was not metabolized further. Cells were unable to take up the lactose analog, methyl-beta-D-thiogalactopyranoside. These data suggest that beta-galactosidase of F. succinogenes L2 cleaves lactose outside the cells and that the glucose released is catabolized while the galactose accumulates in the extracellular culture fluid.     

Effect of extracellular pH on growth and proton motive force of Bacteroides succinogenes, a cellulolytic ruminal bacterium.

The utilization of cellulose or cellobiose by Bacteroides succinogenes S85 was severely inhibited at pH values of less than 5.7. Since low pH inhibited the utilization of both cellobiose and cellulose, changes in cellulase activity could not explain the effect. At an extracellular pH of 6.9, the pH gradient (delta pH) across the cell membrane was only 0.07 U. As extracellular pH declined from 6.9 to 5.7, intracellular pH decreased to a smaller extent than extracellular pH and delta pH increased. Below pH 5.7, there was a linear and nearly proportional decrease in intracellular pH. B. succinogenes took up the lipophilic cation tetraphenylphosphonium ion (TPP+) in the presence of cellobiose, and uptake was sensitive to the ionophore valinomycin. As pH was decreased with phosphoric acid, the cells lost TPP+ and electrical potential, delta psi, decreased. From extracellular pH 6.9 to 5.7, the decrease in delta psi was compensated for by an increase in delta pH, and the proton motive force ranged from 152 to 158 mV. At a pH of less than 5.7, there was a large decrease in proton motive force, and this decrease corresponded to the inhibition of cellobiose utilization.     

Effect of extracellular pH on growth and proton motive force of Bacteroides succinogenes, a cellulolytic ruminal bacterium

The utilization of cellulose or cellobiose by Bacteroides succinogenes S85 was severely inhibited at pH values of less than 5.7. Since low pH inhibited the utilization of both cellobiose and cellulose, changes in cellulase activity could not explain the effect. At an extracellular pH of 6.9, the pH gradient (delta pH) across the cell membrane was only 0.07 U. As extracellular pH declined from 6.9 to 5.7, intracellular pH decreased to a smaller extent than extracellular pH and delta pH increased. Below pH 5.7, there was a linear and nearly proportional decrease in intracellular pH. B. succinogenes took up the lipophilic cation tetraphenylphosphonium ion (TPP+) in the presence of cellobiose, and uptake was sensitive to the ionophore valinomycin. As pH was decreased with phosphoric acid, the cells lost TPP+ and electrical potential, delta psi, decreased. From extracellular pH 6.9 to 5.7, the decrease in delta psi was compensated for by an increase in delta pH, and the proton motive force ranged from 152 to 158 mV. At a pH of less than 5.7, there was a large decrease in proton motive force, and this decrease corresponded to the inhibition of cellobiose utilization.     

alpha-Glucuronidase and Other Hemicellulase Activities of Fibrobacter succinogenes S85 Grown on Crystalline Cellulose or Ball-Milled Barley Straw

Fibrobacter succinogenes produces an alpha-glucuronidase which cleaves 4-O-methyl-alpha-d-glucuronic acid from birch wood 4-O-methyl-alpha-d-glucuronoxylan. Very low levels of alpha-glucuronidase activity were detected in extracellular enzyme preparations of F. succinogenes on birch wood xylan substrate. The release of 4-O-methyl-alpha-d-glucuronic acid was enhanced when the birch wood xylan substrate was predigested by either a purified Schizophyllum commune xylanase or a cloned F. succinogenes S85 xylanase. These data suggest that the alpha-glucuronidase is unable to cleave 4-O-methyl-alpha-d-glucuronic acid from intact xylan but can act on unique low-molecular-weight glucuronoxylan fragments created by the cloned F. succinogenes xylanase. The cloned xylanase presumably must account for a small proportion of the indigenous xylanase activity of F. succinogenes cultures, since this xylanase source does not support high glucuronidase activity. The alpha-glucuronidase and associated hemicellulolytic enzymes exhibited higher activities in culture fluid from cells grown on ball-milled barley straw than in that of cellulose-grown cells. The profile of xylanases separated by isoelectric focusing (zymogram) of culture filtrate from cells grown on barley straw was more complex than that of culture filtrates from cells grown on cellulose. These data demonstrate that F. succinogenes produces an alpha-glucuronidase with an exacting substrate specificity which enables extensive cleavage of glucuronic acid residues from xylan as a consequence of synergistic xylanase action.     

13C and 1H NMR study of cellulose metabolism by Fibrobacter succinogenes S85

Fibrobacter succinogenes S85, a cellulolytic rumen bacterium, is very efficient in degrading lignocellulosic substrates and could be used to develop a biotechnological process for the treatment of wastes. In this work, the metabolism of cellulose by F. succinogenes S85 was investigated using in vivo 13C NMR and 13C-filtered spin-echo difference 1H NMR spectroscopy. The degradation of unlabelled cellulose synthesised by Acetobacter xylinum was studied indirectly, in the presence of [1-13C]glucose, by estimating the isotopic dilution of the final bacterial fermentation products (glycogen, succinate, acetate). During the pre-incubation period of F. succinogenes cells with cellulose fibres, some cells ('non-adherent') did not attach to the solid material. Results for 'adherent' cells showed that about one fourth of the glucose units entering F. succinogenes metabolism originated from cellulose degradation. A huge reversal of succinate metabolism pathway and production of large amounts of unlabelled acetate which was observed during incubation with glucose only, was found to be much decreased in the presence of solid substrate. The synthesis of glucose 6-phophate was slightly increased in the presence of cellulose. Results clearly showed that 'non-adherent' cells were able to metabolise glucose very efficiently; consequently the metabolic state of these cells was not responsible for their 'non-adherence' to cellulose fibre.     

Endoglucanase activity and relative expression of glycoside hydrolase genes of Fibrobacter succinogenes S85 grown on different substrates

The endoglucanase activity of cells and extracellular culture fluid of Fibrobacter succinogenes S85 grown on glucose, cellobiose, soluble polysaccharides (beta-glucan, lichenan) and intact plant polysaccharides, was compared. The specific activity of cells grown on cellulose or forages was 6- to 20-fold higher than that of cells grown on soluble substrates, suggesting an induction of endoglucanases by the insoluble substrates. The ratios of cells to extracellular culture fluid endoglucanase activities measured in cultures grown on sugars or insoluble polysaccharides suggested that the endoglucanases induced by the insoluble polysaccharides remained attached to the cells. The mRNA of all the F. succinogenes glycoside hydrolase genes sequenced so far were then quantified in cells grown on glucose, cellobiose or cellulose. The results show that all these genes were transcribed in growing cells, and that they are all overexpressed in cultures grown on cellulose. Endoglucanase-encoding endB and endA(FS) genes, and xylanase-encoding xynC gene appeared the most expressed genes in growing cells. EGB and ENDA are thus likely to play a major role in cellulose degradation in F. succinogenes.     

Purification and properties of an acetylxylan esterase from Fibrobacter succinogenes S85

An acetylxylan esterase (EC 3.1.1.6) was purified to apparent homogeneity from the nonsedimentable extracellular culture fluid of Fibrobacter succinogenes S85 grown on cellulose. This enzyme had an apparent molecular mass of 55 kDa and an isoelectric point of 4.0. The temperature and pH optima were 45 degrees C and 7.0, respectively. The apparent Km and Vmax were 2.7 mM and 9,100 U/mg, respectively, for the hydrolysis of alpha-naphthyl acetate. The enzyme cleaved acetyl residues from birchwood acetylxylan but did not hydrolyze carboxymethylcellulose, larchwood xylan, ferulic acid-arabinose-xylose polymer, p-nitrophenyl-alpha-L-arab-inofuranoside, or longer-chain naphthyl fatty acid esters. The esterase enzyme may play a role in enhancing hemicellulose degradation by F. succinogenes, thereby allowing it greater access to cellulose present in forage cell walls.     

Purification and properties of an acetylxylan esterase from Fibrobacter succinogenes S85.

An acetylxylan esterase (EC 3.1.1.6) was purified to apparent homogeneity from the nonsedimentable extracellular culture fluid of Fibrobacter succinogenes S85 grown on cellulose. This enzyme had an apparent molecular mass of 55 kDa and an isoelectric point of 4.0. The temperature and pH optima were 45 degrees C and 7.0, respectively. The apparent Km and Vmax were 2.7 mM and 9,100 U/mg, respectively, for the hydrolysis of alpha-naphthyl acetate. The enzyme cleaved acetyl residues from birchwood acetylxylan but did not hydrolyze carboxymethylcellulose, larchwood xylan, ferulic acid-arabinose-xylose polymer, p-nitrophenyl-alpha-L-arab-inofuranoside, or longer-chain naphthyl fatty acid esters. The esterase enzyme may play a role in enhancing hemicellulose degradation by F. succinogenes, thereby allowing it greater access to cellulose present in forage cell walls.     

The use of 16S rRNA-targeted oligonucleotide probes to study competition between ruminal fibrolytic bacteria: development of probes for Ruminococcus species and evidence for bacteriocin production.

A total of six oligonucleotide probes, complementary to the 16S rRNA, were evaluated for quantitative and determinative studies of Ruminococcus albus and Ruminococcus flavefaciens. On the basis of specificity studies, probes for R. albus (probe RAL196) and R. flavefaciens (probe RFL196) were selected to quantitate these species in mixed culture. In combination with a Fibrobacter succinogenes S85 subspecies probe (SUB1) and a domain Bacteria (formerly kingdom Eubacteria) probe (EUB338), they were used to quantitate these species competing in mixed cultures for cellobiose as the carbon source. In dicultures containing R. albus 8 and F. succinogenes S85, competition was not observed. However, R. flavefaciens FD-1 eventually outcompeted F. succinogenes S85 when cellobiose was the substrate. When R. albus 8 and R. flavefaciens FD-1 were grown together on cellobiose medium, R. albus 8 outcompeted R. flavefaciens FD-1, resulting in undetectable R. flavefaciens 16S rRNA only 1 to 3 h after inoculation, suggesting production of an antagonistic compound by R. albus 8 during rapid growth on soluble substrates. Further, when R. albus 8, R. flavefaciens FD-1, and F. succinogenes S85 were grown together in a triculture, R. flavefaciens FD-1 16S rRNA was detectable for only 2 h after inoculation, while R. albus 8 and F. succinogenes S85 showed a similar competition pattern to that of the dicultures. The results show that the Ruminococcus probes were effective in the measurement of relative populations of selected R. albus and R. flavefaciens strains during in vitro competition studies with F. succinogenes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cloning of a xylanase gene from Fibrobacter succinogenes 135 and its expression in Escherichia coli

A genomic library consisting of 4- to 7-kb EcoRI DNA fragments from Fibrobacter succinogenes 135 was constructed using a phage vector, lambda gtWES lambda B, and Escherichia coli ED8654 as the host bacterium. Two positive plaques, designated lambda FSX101 and lambda FSX102, were identified. The inserts were 10.5 and 9.8 kb, respectively. A 2.3-kb EcoRI fragment that was subcloned from lambda FSX101 into pBR322 also showed xylanase activity. Southern blot analysis showed that the cloned EcoRI fragment containing the xylanase gene had originated from F. succinogenes 135. The cloned endo-(1,4)-beta-D-xylanase gene (pFSX02) was expressed constitutively in E. coli HB101 when grown on LB and on M9 medium containing either glucose or glycerol as the carbon source. Most of the beta-D-xylanase activity was located in the periplasmic space. Zymogram activity stains of nondenaturing polyacrylamide gels and isoelectric focusing gels showed that several xylanase isoenzymes were present in the periplasmic fraction of the E. coli clone FSX02 and they probably were due to posttranslational modification of a single gene product. Comparison of the FSX02 xylanase and the xylanase from the extracellular culture fluids of F. succinogenes 135 and S85 for their ability to degrade oat spelt xylan showed that, for equal units of beta-D-xylanase activity, hydrolysis by the cloned gene product was more complete. However, unlike the unfractionated mixture of xylanases from F. succinogenes 135 and S85, the enzyme from E. coli FSX02 was unable to release arabinose from oat spelt xylan.     

Outer membrane proteins of Fibrobacter succinogenes with potential roles in adhesion to cellulose and in cellulose digestion

Comparative analysis of binding of intact glucose-grown Fibrobacter succinogenes strain S85 cells and adhesion-defective mutants AD1 and AD4 to crystalline and acid-swollen (amorphous) cellulose showed that strain S85 bound efficiently to both forms of cellulose while mutant Ad1 bound to acid-swollen cellulose, but not to crystalline cellulose, and mutant Ad4 did not bind to either. One- and two-dimensional electrophoresis (2-DE) of outer membrane cellulose binding proteins and of outer membranes, respectively, of strain S85 and adhesion-defective mutant strains in conjunction with mass spectrometry analysis of tryptic peptides was used to identify proteins with roles in adhesion to and digestion of cellulose. Examination of the binding to cellulose of detergent-solubilized outer membrane proteins from S85 and mutant strains revealed six proteins in S85 that bound to crystalline cellulose that were absent from the mutants and five proteins in Ad1 that bound to acid-swollen cellulose that were absent from Ad4. Twenty-five proteins from the outer membrane fraction of cellulose-grown F. succinogenes were identified by 2-DE, and 16 of these were up-regulated by growth on cellulose compared to results with growth on glucose. A protein identified as a Cl-stimulated cellobiosidase was repressed in S85 cells growing on glucose and further repressed in the mutants, while a cellulose-binding protein identified as pilin was unchanged in S85 grown on glucose but was not produced by the mutants. The candidate differential cellulose binding proteins of S85 and the mutants and the proteins induced by growth of S85 on cellulose provide the basis for dissecting essential components of the cellulase system of F. succinogenes.     

The use of 16S rRNA-targeted oligonucleotide probes to study competition between ruminal fibrolytic bacteria: pure-culture studies with cellulose and alkaline peroxide-treated wheat straw.

Specific oligonucleotide probes targeted to sites on the 16S rRNA of Ruminococcus albus 8, Ruminococcus flavefaciens FD-1, and Fibrobacter succinogenes S85 and a domain Bacteria probe were used to study bacterial interactions during the fermentation of cellulose and alkaline hydrogen peroxide-treated wheat straw in monocultures, dicultures, and tricultures. Results showed that R. albus 8 inhibited the growth of R. flavefaciens FD-1 when grown as a diculture with cellulose or alkaline hydrogen peroxide-treated wheat straw as the carbon source. In dicultures containing R. albus 8 and F. succinogenes S85 grown on cellulose or alkaline hydrogen peroxide-treated wheat straw, competition was not detected. R. flavefaciens FD-1 outcompeted F. succinogenes S85 when cellulose was used as the carbon source. In tricultures with cellulose as the carbon source, R. flavefaciens FD-1 was inhibited, R. albus 8 appeared to dominate during the early phase of degradation (12 to 48 h), while F. succinogenes S85 became predominant during the later phase of degradation (60 to 70 h). When alkaline hydrogen peroxide-treated wheat straw was used as a growth substrate, F. succinogenes S85 showed better growth than either R. albus 8 or R. flavefaciens FD-1. However, R. flavefaciens FD-1 was present in small numbers throughout the incubation period, unlike the growth patterns when cellulose was the carbon source.     

Antigenic nature of the chloride-stimulated cellobiosidase and other cellulases of Fibrobacter succinogenes subsp. succinogenes S85 and related fresh isolates.

Polyclonal and monoclonal antibodies to the Cl-stimulated cellobiosidase of Fibrobacter succinogenes subsp. succinogenes S85 reacted with numerous proteins of both higher and lower molecular weights from F. succinogenes subsp. succinogenes S85, but not with Escherichia coli proteins, and only one protein each from Butyrivibrio fibrisolvens and Ruminococcus albus. Different profiles were observed for Western blots (immunoblots) of peptide digests of both the purified enzyme from F. succinogenes and immunoreactive proteins of higher and lower molecular weights, demonstrating that they were different proteins. Therefore, F. succinogenes appeared to produce numerous proteins with one or more common antigenic determinants. However, with the exception of Cl-stimulated cellobiosidase, none were cellulases that have been characterized. An affinity-purified polyclonal antibody to Cl-stimulated cellobiosidase reacted with numerous proteins in cells of each of three fresh isolates of F. succinogenes subsp. succinogenes and one of F. succinogenes subsp. elongata when analyzed by Western blotting. Antibodies to periplasmic cellodextrinase, endoglucanase 2 (EG2), and EG3, when reacted in Western blots with the various cellulases, including Cl-stimulated cellobiosidase, revealed limited antigenic similarity among the different proteins and none with either B. fibrisolvens or R. albus proteins. The periplasmic cellodextrinase antibody reacted with an antigen with a size corresponding to cellodextrinase in each of the three F. succinogenes subsp. succinogenes isolates but not with any antigens from the F. succinogenes subsp. elongata isolate. The anti-EG2 antibody reacted with single antigens in each of the four isolates, while the anti-EG3 antibody reacted with only one of the four isolates.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization of a family 45 glycosyl hydrolase from Fibrobacter succinogenes S85

Fibrobacter succinogenes is one of the most active cellulolytic bacteria ever isolated from the rumen, but enzymes from F. succinogenes capable of hydrolyzing native (insoluble) cellulose at a rapid rate have not been identified. However, the genome sequence of F. succinogenes is now available, and it was hoped that this information would yield new insights into the mechanism of cellulose digestion. The genome has a single family 45 beta-glucanase gene, and some of the enzymes in this family have good activity against native cellulose. The gene encoding the family 45 glycosyl hydrolase from F. succinogenes S85 was cloned into Escherichia coli JM109(DE3) using pMAL-c2 as a vector. Recombinant E. coli cells produced a soluble fusion protein (MAL-F45) that was purified on a maltose affinity column and characterized. MAL-F45 was most active on carboxymethylcellulose between pH 6 and 7 and it hydrolyzed cellopentaose and cellohexaose but not cellotetraose. It also cleaved p-nitrophenyl-cellopentose into cellotriose and p-nitrophenyl-cellobiose. MAL-F45 produced cellobiose, cellotriose and cellotetraose from acid swollen cellulose and bacterial cellulose, but the rate of this hydrolysis was much too low to explain the rate of cellulose digestion by growing cultures. Because the F. succinogenes S85 genome lacks dockerin and cohesin sequences, does not encode any known processive cellulases, and most of its endoglucanase genes do not encode carbohydrate binding modules, it appears that F. succinogenes has a novel mechanism of cellulose degradation.     

Esterase Activities of Fibrobacter succinogenes subsp. succinogenes S85

Cells of the anaerobic ruminal bacterium Fibrobacter succinogenes subsp. succinogenes S85 (formerly Bacteroides succinogenes) exhibit arylesterase activity. When cells were grown on cellulose, it was found that 69% of the total esterase activity was extracellular while 65% was nonsedimentable upon centrifugation of the culture supernatant at 100,000 x g. Disruption of the cells by various different methods failed to increase the esterase activity, indicating that the substrate was fully accessible to esterase enzymes in intact cells. During growth of cells with either glucose or cellulose as the sole carbon source, the increase in acetylesterase activity corresponded to an increase in cell density, suggesting constitutive production. The enzyme(s) hydrolyzed alpha-naphthyl, p-nitrophenyl, and 4-methylumbelliferyl derivatives of acetic acid; xylose tetraacetate; glucose pentaacetate; acetylxylan; and a polymer composed of ferulic acid, arabinose, and xylose in molar proportions of 1:1.1:2.2 (FAX). These data demonstrate the presence of an acetylxylan esterase and a ferulic acid esterase. The cleavage of FAX also documents the presence of an alpha-l-arabinofuranosidase.     

Antigenic nature of the chloride-stimulated cellobiosidase and other cellulases of Fibrobacter succinogenes subsp. succinogenes S85 and related fresh isolates.

Polyclonal and monoclonal antibodies to the Cl-stimulated cellobiosidase of Fibrobacter succinogenes subsp. succinogenes S85 reacted with numerous proteins of both higher and lower molecular weights from F. succinogenes subsp. succinogenes S85, but not with Escherichia coli proteins, and only one protein each from Butyrivibrio fibrisolvens and Ruminococcus albus. Different profiles were observed for Western blots (immunoblots) of peptide digests of both the purified enzyme from F. succinogenes and immunoreactive proteins of higher and lower molecular weights, demonstrating that they were different proteins. Therefore, F. succinogenes appeared to produce numerous proteins with one or more common antigenic determinants. However, with the exception of Cl-stimulated cellobiosidase, none were cellulases that have been characterized. An affinity-purified polyclonal antibody to Cl-stimulated cellobiosidase reacted with numerous proteins in cells of each of three fresh isolates of F. succinogenes subsp. succinogenes and one of F. succinogenes subsp. elongata when analyzed by Western blotting. Antibodies to periplasmic cellodextrinase, endoglucanase 2 (EG2), and EG3, when reacted in Western blots with the various cellulases, including Cl-stimulated cellobiosidase, revealed limited antigenic similarity among the different proteins and none with either B. fibrisolvens or R. albus proteins. The periplasmic cellodextrinase antibody reacted with an antigen with a size corresponding to cellodextrinase in each of the three F. succinogenes subsp. succinogenes isolates but not with any antigens from the F. succinogenes subsp. elongata isolate. The anti-EG2 antibody reacted with single antigens in each of the four isolates, while the anti-EG3 antibody reacted with only one of the four isolates.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fiber-degrading systems of different strains of the genus Fibrobacter

The S85 type strain of Fibrobacter succinogenes, a major ruminal fibrolytic species, was isolated 49 years ago from a bovine rumen and has been used since then as a model for extensive studies. To assess the validity of this model, we compared the cellulase- and xylanase-degrading activities of several other F. succinogenes strains originating from different ruminants, including recently isolated strains, and looked for the presence of 10 glycoside hydrolase genes previously identified in S85. The NR9 F. intestinalis type strain, representative of the second species of the genus, was also included in this study. DNA-DNA hybridization and 16S rRNA gene sequencing first classified the strains and provided the phylogenetic positions of isolates of both species. Cellulase and xylanase activity analyses revealed similar activity profiles for all F. succinogenes strains. However, the F(E) strain, phylogenetically close to S85, presented a poor xylanolytic system and weak specific activities. Furthermore, the HM2 strain, genetically distant from the other F. succinogenes isolates, displayed a larger cellulolytic profile on zymograms and higher cellulolytic specific activity. F. intestinalis NR9 presented a higher cellulolytic specific activity and a stronger extracellular xylanolytic activity. Almost all glycoside hydrolase genes studied were found in the F. succinogenes isolates by PCR, except in the HM2 strain, and few of them were detected in F. intestinalis NR9. As expected, the fibrolytic genes of strains of the genus Fibrobacter as well as the cellulase and xylanase activities are better conserved in closely related phylogenetic isolates.     

Production of maltodextrin 1-phosphate by Fibrobacter succinogenes S85

We show for the first time the occurrence of maltodextrin-1-Phosphate (MD-1P) (DP2) in F. succinogenes S85, a rumen bacterium specialized in cellulolysis which is not able to use maltose and starch. MD-1P were found in intra and extracellular medium of resting cells incubated with glucose. We used 2D 1H NMR technique and TLC to identify their structure and quantify their production with time. It was also shown that these phosphorylated oligosaccharides originated both from exogenous glucose and endogenous glycogen.     

Concurrent maltodextrin and cellodextrin synthesis by Fibrobacter succinogenes S85 as identified by 2D NMR spectroscopy.

1D and 2D NMR experiments were used to analyse the synthesis of various metabolites by resting cells of Fibrobacter succinogenes S85 when incubated with [1-(13)C]glucose, in both extracellular and cellular media. Besides the expected glycogen, succinate, acetate, glucose-1-P and glucose-6-P, maltodextrins and cellodextrins were detected. Maltodextrins were excreted into the external medium. They were found to have linear structures with a maximum degree of polymerization (DP) of about 6 or 7 units. Cellodextrins were located in the cells (cytoplasm and/or periplasm), and their DP was < or = 4. Both labelled (1-(13)C and 6-(13)C) and unlabelled maltodextrins and cellodextrins were detected, showing the contribution of carbohydrate cycling in F. succinogenes, including the reversal of glycolysis and the futile cycle of glycogen. The mechanisms of these oligosaccharide syntheses are discussed.