Cellulose digestion and cellulase regulation and distribution in Fibrobacter succinogenes subsp. succinogenes S85.

Fibrobacter succinogenes subsp. succinogenes S85 initiated growth on microcrystalline cellulose without a lag whether inoculated from a glucose, cellobiose, or cellulose culture. During growth on cellulose, there was no accumulation of soluble carbohydrate. When the growth medium contained either glucose or cellobiose in combination with microcrystalline cellulose, there was a lag in cellulose digestion until all of the soluble sugar had been utilized, suggesting an end product feedback mechanism that affects cellulose digestion. Cl-stimulated cellobiosidase and periplasmic cellodextrinase were produced under all growth conditions tested, indicating constitutive synthesis. Both cellobiosidases were cell associated until the stationary phase of growth, whereas proteins antigenically related to the Cl-stimulated cellobiosidase and a proportion of the endoglucanase were released into the extracellular culture fluid during growth, irrespective of the substrate. Immunoelectron microscopy of cells with a polyclonal antibody to Cl-stimulated cellobiosidase as the primary antibody and 10-nm-diameter gold particles conjugated to goat anti-rabbit antibodies as the second antibody revealed protrusions of the outer surface which were selectively labeled with gold, suggesting that Cl-stimulated cellobiosidase was located on the protrusions. These data support the contention that the protrusions have a role in cellulose hydrolysis; however, this interpretation is complicated by reactivity of the antibodies with a large number of other proteins that possess related antigenic epitopes.     

Regulation and distribution of Fibrobacter succinogenes subsp. succinogenes S85 endoglucanases

The distribution of endoglucanase activities in cultures of Fibrobacter succinogenes subsp. succinogenes S85 grown on different carbon sources was examined by a variety of biochemical and immunological techniques. Total culture endoglucanase activity was primarily cell associated and was expressed constitutively, although synthesis of endoglucanase 1 (EG1) was repressed by cellobiose. Western immunoblotting showed that EG1 and EG3 were released into the culture fluid during growth, while EG2 remained largely associated with the cell. Subcellular localization showed low endoglucanase activity in the periplasmic fraction and similar, high levels in the cytoplasmic and membrane fractions. Western immunoblotting showed that EG2 was absent from the periplasmic fraction. Data from immunoelectron microscopy with either polyclonal or monoclonal antibody to EG2 revealed a high density of gold labeling at sites where there was a disruption in the regular features of the cell surface, such as in blebbing or physical tearing of the membrane. When cells were grown on cellulose, there was a high density of labeling on the cellulose but not on the cells, indicating that EG2 has limited exposure at the cell surface. On the basis of these data, export of enzymes from their intracellular locations appears to occur via three different mechanisms: a specific secretory pathway independent of cellulose, a secretory mechanism which is mediated by contact with cellulose, and a generalized blebbing process that occurs irrespective of the carbon source.     

Regulation and distribution of Fibrobacter succinogenes subsp. succinogenes S85 endoglucanases.

The distribution of endoglucanase activities in cultures of Fibrobacter succinogenes subsp. succinogenes S85 grown on different carbon sources was examined by a variety of biochemical and immunological techniques. Total culture endoglucanase activity was primarily cell associated and was expressed constitutively, although synthesis of endoglucanase 1 (EG1) was repressed by cellobiose. Western immunoblotting showed that EG1 and EG3 were released into the culture fluid during growth, while EG2 remained largely associated with the cell. Subcellular localization showed low endoglucanase activity in the periplasmic fraction and similar, high levels in the cytoplasmic and membrane fractions. Western immunoblotting showed that EG2 was absent from the periplasmic fraction. Data from immunoelectron microscopy with either polyclonal or monoclonal antibody to EG2 revealed a high density of gold labeling at sites where there was a disruption in the regular features of the cell surface, such as in blebbing or physical tearing of the membrane. When cells were grown on cellulose, there was a high density of labeling on the cellulose but not on the cells, indicating that EG2 has limited exposure at the cell surface. On the basis of these data, export of enzymes from their intracellular locations appears to occur via three different mechanisms: a specific secretory pathway independent of cellulose, a secretory mechanism which is mediated by contact with cellulose, and a generalized blebbing process that occurs irrespective of the carbon source.     

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.     

Kinetics of Cellulose Digestion by Fibrobacter succinogenes S85

Growing cultures of Fibrobacter succinogenes S85 digested cellulose at a rapid rate, but nongrowing cells and cell extracts did not have detectable crystalline cellulase activity. Cells that had been growing exponentially on cellobiose initiated cellulose digestion and succinate production immediately, and cellulose-dependent succinate production could be used as an index of enzyme activity against crystalline cellulose. Cells incubated with cellulose never produced detectable cellobiose, and cells that were preincubated for a short time with thiocellobiose lost their ability to digest cellulose (competitive inhibition [K(infi)] of only 0.2 mg/ml or 0.56 mM). Based on these results, the crystalline cellulases of F. succinogenes were very sensitive to feedback inhibition. Different cellulose sources bound different amounts of Congo red, and the binding capacity was HCl-regenerated cellulose > ball-milled cellulose > Sigmacel > Avicel > filter paper. Congo red binding capacity was highly correlated with the maximum rates of metabolism of cellulose digestion and inversely related to K(infm). Congo red (250 (mu)g/ml) did not inhibit the growth of F. succinogenes S85 on cellobiose, but this concentration of Congo red inhibited the rate of ball-milled cellulose digestion. A Lineweaver-Burk plot of ball-milled cellulose digestion rate versus the amount of cellulose indicated that Congo red was a competitive inhibitor of cellulose digestion (K(infi) was 250 (mu)g/ml).     

Evaluating Models of Cellulose Degradation by Fibrobacter succinogenes S85

Fibrobacter succinogenes S85 is an anaerobic non-cellulosome utilizing cellulolytic bacterium originally isolated from the cow rumen microbial community. Efforts to elucidate its cellulolytic machinery have resulted in the proposal of numerous models which involve cell-surface attachment via a combination of cellulose-binding fibro-slime proteins and pili, the production of cellulolytic vesicles, and the entry of cellulose fibers into the periplasmic space. Here, we used a combination of RNA-sequencing, proteomics, and transmission electron microscopy (TEM) to further clarify the cellulolytic mechanism of F. succinogenes. Our RNA-sequence analysis shows that genes encoding type II and III secretion systems, fibro-slime proteins, and pili are differentially expressed on cellulose, relative to glucose. A subcellular fractionation of cells grown on cellulose revealed that carbohydrate active enzymes associated with cellulose deconstruction and fibro-slime proteins were greater in the extracellular medium, as compared to the periplasm and outer membrane fractions. TEMs of samples harvested at mid-exponential and stationary phases of growth on cellulose and glucose showed the presence of grooves in the cellulose between the bacterial cells and substrate, suggesting enzymes work extracellularly for cellulose degradation. Membrane vesicles were only observed in stationary phase cultures grown on cellulose. These results provide evidence that F. succinogenes attaches to cellulose fibers using fibro-slime and pili, produces cellulases, such as endoglucanases, that are secreted extracellularly using type II and III secretion systems, and degrades the cellulose into cellodextrins that are then imported back into the periplasm for further digestion by β-glucanases and other cellulases.     

Factors affecting adhesion of Fibrobacter succinogenes subsp. succinogenes S85 and adherence-defective mutants to cellulose

Fibrobacter succinogenes subsp. succinogenes S85, formerly Bacteroides succinogenes, adheres to crystalline cellulose present in the culture medium. When the cells are suspended in buffer, adhesion is enhanced by increasing the ionic strength. Heat, glutaraldehyde, trypsin, and pronase treatments markedly reduce the extent of adhesion. Treatment with dextrinase, modification of amino and carboxyl groups with Formalin or other chemical agents, and inclusion of either albumin (1%) or Tween 80 (0.5%) do not decrease the degree of adhesion. Adherence-defective mutants isolated by their inability to bind to cellulose exhibited different growth characteristics. Class 1 mutants grew on glucose, cellobiose, amorphous cellulose, and crystalline cellulose. Class 3 mutants grew on glucose and cellobiose but not on amorphous or crystalline cellulose. No substantial changes were detected in the endoglucanase, cellobiosidase, and cellobiase activities of the wild type and the mutants. These data suggest that adhesion to crystalline cellulose is specific and that it involves surface proteins.     

Characterization of the NADH dehydrogenase and fumarate reductase of Fibrobacter succinogenes subsp. succinogenes S85

Conditions promoting maximal in vitro activity of the particulate NADH:fumarate reductase from Fibrobacter succinogenes were determined. This system showed a pH optimum of 6.0 in K⁺ MES buffer only when salt (NaCl or KCl) was present. Salt stimulated the activity eightfold at the optimal concentration of 150m M. This effect was due to stimulation of fumarate reductase activity as salt had little effect on NADH: decylubiquinone oxidoreductase (NADH dehydrogenase). The stimulation of fumarate reductase by salt at pH 6.0 was not due to removal of oxaloacetate from the enzyme. Kinetic parameters for several inhibitors were also measured. NADH dehydrogenase was inhibited by rotenone at a single site with a K _i of 1 M. 2-Heptyl-4-hydroxyquinonline-N-oxide (HOQNO) inhibited NADH: fumarate reductase with a K _i of 0.006 M, but NADH dehydrogenase exhibited two HOQNO inhibition constants of approximately 1 M and 24 M. Capsaicin and laurylgallate each inhibited NADH dehydrogenase by only 20% at 100 M. NADH dehydrogenase gave K _m values of 1 M for NADH and 4 M for reduced hypoxanthine adenine dinucleotide.Published with the approval of the Director of the Agricultural Experiment Station, North Dakota State University, as journal article no. 2201     

Factors affecting adhesion of Fibrobacter succinogenes subsp. succinogenes S85 and adherence-defective mutants to cellulose.

Fibrobacter succinogenes subsp. succinogenes S85, formerly Bacteroides succinogenes, adheres to crystalline cellulose present in the culture medium. When the cells are suspended in buffer, adhesion is enhanced by increasing the ionic strength. Heat, glutaraldehyde, trypsin, and pronase treatments markedly reduce the extent of adhesion. Treatment with dextrinase, modification of amino and carboxyl groups with Formalin or other chemical agents, and inclusion of either albumin (1%) or Tween 80 (0.5%) do not decrease the degree of adhesion. Adherence-defective mutants isolated by their inability to bind to cellulose exhibited different growth characteristics. Class 1 mutants grew on glucose, cellobiose, amorphous cellulose, and crystalline cellulose. Class 3 mutants grew on glucose and cellobiose but not on amorphous or crystalline cellulose. No substantial changes were detected in the endoglucanase, cellobiosidase, and cellobiase activities of the wild type and the mutants. These data suggest that adhesion to crystalline cellulose is specific and that it involves surface proteins.     

Two beta-glucosidase activities in Fibrobacter succinogenes S85.

Few bacteria are capable of degrading crystalline cellulose but there is considerable interest in the properties of enzyme systems with this capability. In the bovine and ovine rumen the principal cellulolytic bacterium is Fibrobacter (formerly Bacteroides) succinogenes. The cellulase system of this organism is composed of multiple enzyme components, including a constitutive and cell-associated beta-glucosidase active against cellobiose. The properties of the beta-glucosidase activity have been investigated with the chromogenic substrate p-nitrophenyl beta-D-glucoside (pNPG). Hydrolytic activity against pNPG was located primarily in the cytoplasm and the cytoplasmic membrane but showed a gradual migration to the periplasm during growth on either glucose or cellobiose. Activity against cellobiose was found in the periplasm in significant amounts in all growth phases. Of the beta-glucosides tested, only cellobiose and pNPG were hydrolysed by crude cell extracts. In the presence of cellobiose, however, the rate of hydrolysis of pNPG was stimulated up to 10-fold, and extracts hydrolysed methylumbelliferyl beta-D-glucoside, 5-bromo-4-chloro-3-indolyl beta-D-glucoside, arbutin and aesculin. Activities against pNPG in the presence and absence of cellobiose displayed similar instability in the presence of oxygen; both were stabilized by dithiothreitol and the temperature and pH optima were identical. A significant proportion of the membrane-associated beta-glucosidase was released by treatment with 0.3 mol/1 KCl, and fractionation by chromatography on CM-cellulose showed the presence of two activities against pNPG, only one of which was stimulated by cellobiose.     

Fibrobacter succinogenes S85 has multiple xylanase genes

Four distinct DNA fragments encoding xylanase activities, pBX1.2, pXC30.2, pX14 and LX31, were cloned from plasmid and γ libraries constructed using genomic DNA from Fibrobacter succinogenes S85. pBX1.2 contained an insert which was homologous, and mapped similarly to that previously cloned in pBX1 while the three remaining clones pX14, pXC30 in plasmids, and LX31 in lambda, represented new xylanase activities. The X14 xylanase was a 73 kDa exo-type xylanase, which was exported to the periplasm of the Escherichia coli host, and produced large quantities of xylose and xylobiose from oat spelt xylan. The XC30 xylanase, also exported in E. coli, was a 77 kDa protein which exhibited both xylanase and endoglucanase activities, and a low cellobiosidase activity. The LX31 enzyme was a 58 kDa endoxylanase that produced a mixture of xylooligosaccharides. Zymograms of isoelectric focusing gels showed that the X14 xylanase had a neutral pI, XC30 contained acidic, neutral and basic enzymic components, while BX1 and LX31 were acidic. These results indicate that, in addition to the many other elements of its polysaccharide-degrading repertoire, F. succinogenes S85 possesses at least four distinct xylanases.     

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)     

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)     

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.     

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.     

Two β-glucosidase activities in Fibrobacter succinogenes S85

Few bacteria are capable of degrading crystalline cellulose but there is considerable interest in the properties of enzyme systems with this capability. In the bovine and ovine rumen the principal cellulolytic bacterium is Fibrobacter (formerly Bacteroides ) succinogenes. The cellulase system of this organism is composed of multiple enzyme components, including a constitutive and cell-associated β -glucosidase active against cellobiose. The properties of the β -glucosidase activity have been investigated with the chromogenic substrate β -nitrophenyl β -D-glucoside (pNPG). Hydrolytic activity against pNPG was located primarily in the cytoplasm and the cytoplasmic membrane but showed a gradual migration to the periplasm during growth on either glucose or cellobiose. Activity against cellobiose was found in the periplasm in significant amounts in all growth phases. Of the β -glucosides tested, only cellobiose and pNPG were hydrolysed by crude cell extracts. In the presence of cellobiose, however, the rate of hydrolysis of pNPG was stimulated up to 10-fold, and extracts hydrolysed methylumbelliferyl β -D-glucoside, 5-bromo-4-chloro-3-indolyl β -D-glucoside, arbutin and aesculin. Activities against pNPG in the presence and absence of cellobiose displayed similar instability in the presence of oxygen; both were stabilized by dithiothreitol and the temperature and pH optima were identical. A significant proportion of the membrane-associated β -glucosidase was released by treatment with 0.3 mol/1 KCl, and fractionation by chromatography on CM-cellulose showed the presence of two activities against pNPG, only one of which was stimulated by cellobiose.     

Oligosaccharide synthesis in Fibrobacter succinogenes S85 and its modulation by the substrate

In this article we compared the metabolism of phosphorylated and unphosphorylated oligosaccharides (cellodextrins and maltodextrins) in Fibrobacter succinogenes S85 resting cells incubated with the following substrates: glucose; cellobiose; a mixture of glucose and cellobiose; and cellulose. Intracellular and extracellular media were analysed by (1)H-NMR and by TLC. The first important finding is that no cellodextrins were found to accumulate in the extracellular media of cells, regardless of the substrate; this contrasts to what is generally reported in the literature. The second finding of this work is that maltodextrins of degree of polymerization > 2 are synthesized regardless of the substrate, and can be used by the bacteria. Maltotriose plays a key role in this metabolism of maltodextrin. Maltodextrin-1-phosphate was detected in all the incubations, and a new metabolite, corresponding to a phosphorylated glucose derivative, was produced in the extracellular medium when cells were incubated with cellulose. The accumulation of these phosphorylated sugars increased with the degree of polymerization of the substrate.     

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.     

A cold-active glucanase from the ruminal bacterium Fibrobacter succinogenes S85

We previously characterized two endoglucanases, CelG and EGD, from the mesophilic ruminal anaerobe Fibrobacter succinogenes S85. Further comparative experiments have shown that CelG is a cold-active enzyme whose catalytic properties are superior to those of several other intensively studied cold-active enzymes. It has a lower temperature optimum, of 25 degrees C, and retains about 70% of its maximum activity at 0 degrees C, while EGD has a temperature optimum of 35 degrees C and retains only about 18% of its maximal activity at 0 degrees C. When assayed at 4 degrees C, CelG exhibits a 33-fold-higher kcat value and a 73-fold-higher physiological efficiency (kcat/Km) than EGD. CelG has a low thermal stability, as indicated by the effect of temperature on its activity and secondary structure. The presence of small amino acids around the putative catalytic residues may add to the flexibility of the enzyme, thereby increasing its activity at cold temperatures. Its activity is modulated by sodium chloride, with an increase of over 1.8-fold at an ionic strength of 0.03. Possible explanations for the presence of a cold-active enzyme in a mesophile are that cold-active enzymes are more broadly distributed than previously expected, that lateral transfer of the gene from a psychrophile occurred, or that F. succinogenes originated from the marine environment.     

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.