from Streptomyces chattanoogensis CECT 3336 - Springer Link

Appl Microbiol Biotechnol (1998) 50: 284±287

Ó Springer-Verlag 1998

SHORT CONTRIBUTION

C. L. LoÂpez-FernaÂndez á J. RodrõÂ guez á A. S. Ball J. L. Copa-PatinÄo á M. I. PeÂrez-Leblic á M. E. Arias

Application of the af®nity binding of xylanases to oat-spelt xylan in the puri®cation of endoxylanase CM-2 from Streptomyces chattanoogensis CECT 3336 Received: 6 April 1998 / Accepted: 8 May 1998

Abstract The use of the insoluble polysaccharides Avicel and oat-spelt xylan for the binding and subsequent puri®cation of active xylanases from Streptomyces chattanoogensis was investigated. Maximum recovery of xylanases was achieved with oat-spelt xylan, using NaCl (2 M) to remove active protein. The application of this technique to the puri®cation of xylanases resulted in the puri®cation of an endoxylanase (CM-2) with high speci®c activity (729.5 U mg)1). The properties of the puri®ed enzyme, exhibiting activity and stability between 40 °C and 60 °C and between pH 5 and 8, suggest a potential role for both the enzyme and the rapid puri®cation protocol in the removal of hemicelluloses from kraft pulp prior to bleaching.

Introduction Recent biotechnological interest in xylanases has focused on the application of these enzymes to the pulp and paper industry where they have been used for the selective removal of hemicelluloses from kraft pulp prior to pulp bleaching (Vikarii et al. 1994). Xylanases may also be used to increase the digestibility of animal feedstock and in the baking and brewing industries (Wong and Saddler 1993). Prior to use, however, separation followed by puri®cation of these enzymes from a range of other extracellular enzymes such as cellulases C. L. LoÂpez-FernaÂndez á J. Rodrõ guez á J. L. Copa-PatinÄo M. I. PeÂrez-Leblic á M. E. Arias (&) Departamento de Microbiologõ a y Parasitologõ a, Universidad de AlcalaÂ, 28871 Alcala de Henares, Madrid, Spain e-mail: MPMAF@ MICROB.ALCALA.ES Tel.: +34-1-8854633 Fax: +34-1-8854623 A. S. Ball Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, CO43SQ, UK

must be achieved (Vikarii et al. 1994). Although methods for the puri®cation of xylanases are now well documented, these techniques require a number of expensive puri®cation steps, each of which reduce the overall yield of enzyme activity, which can be less than 5% of the original value (Wang et al. 1993). We have previously reported the isolation of Streptomyces chattanoogensis, a microorganism capable of producing xylanase activity (1.3 U ml)1) with no detectable cellulase activities (LoÂpez FernaÂndez et al. 1995). In this paper we report the application of anity binding for the rapid puri®cation of endoxylanase activity, enabling large quantities of pure, stable endoxylanases to be assessed for their biotechnological potential.

Materials and methods Strain and growth conditions Streptomyces chattanoogensis was maintained as a spore suspension in 20% (v/v) glycerol at )70 °C. This strain was identi®ed in the light of the criteria described by Williams et al. (1989) and was deposited in the Spanish Type Culture Collection with the complete name Streptomyces chattanoogensis CECT 3336. Flasks (100 ml) containing 25 ml basal medium (Crawford 1978), supplemented with yeast extract (6 g l)1) and oat-spelt xylan (Sigma, 1% w/v) were inoculated with a spore suspension and incubated for 4 days at 28 °C and 200 rev min)1.

Sampling and chemical analysis Triplicate samples were used throughout the study. The mycelium and the insoluble substrate were separated from the culture supernatant by centrifugation at 4000 g for 20 min. Culture supernatants were assayed for extracellular protein content, pH, the presence of reducing sugars and for xylanase and cellulase activities. Intracellular protein (used as an index of growth) was determined after the pelleted material had been boiled with NaOH (5 ml; 1 M) for 20 min. Intra- and extracellular proteins were estimated by the method of Bradford (1976).

285 Enzyme assays

Enzyme characterization

Xylanase assay Enzyme solution …25 ll† was mixed with an oat-spelt xylan suspension (25 ll; 0.4% w/v) in phosphate bu€er (10 mM, pH 7.0) and the mixture incubated at 55 °C for 10 min. At the end of the incubation, the presence of reducing sugars was determined by the bicinchoninate/Cu2+ reagent method (Copa-PatinÄo et al. 1993). One unit (U) of xylanase activity is de®ned as the amount of the enzyme that releases one micromole of xylose per minute.

The temperature optimum and stability of puri®ed xylanase activity were estimated over the range, 40±90 °C. The pH stability and optimum for xylanase activity were determined over the range pH 3.0±9.0 in 50 mM Britton and Robinson universal bu€er (Johnson and Lindsey 1939). Lineweaver-Burk plots were used to calculate Km and Vmax , with both oat-spelt and birchwood xylan used as substrates. The e€ects of metal ions on enzyme activity were investigated by including di€erent metal salts (HgCl2, CuCl, MnCl2, AgNO3) at a ®nal concentration of 1 mM in the reaction mixture for the determination of enzyme activity.

Endoglucanase assay

Glycosylation studies

Cellulase activity was assayed as xylanase but carboxymethycellulose (Sigma; 2% w/v) replaced xylan as substrate. The mixture was incubated at 37 °C for 30 min. One unit (U) of cellulase activity was de®ned as the amount of enzyme that releases one micromole of glucose per minute.

The total carbohydrate content of protein was determined by the phenol/sulphate method (Dubois et al. 1956) with glucose as standard.

Binding studies

Hydrolysis of oat-spelt xylan (0.5% w/v) by the puri®ed xylanase was assessed by thin-layer chromatography (TLC) on silica gel plates ( Yoshida 1990). Aliquots …5 ll† were spotted onto a TLC plate and then partitioned for 2.5 h at room temperature in chloroform/methanol/water (90:65:1, v/v/v).

Xylanases, present either in culture supernatants or in puri®ed fractions, were mixed with di€erent concentrations of Avicel (microcrystalline cellulose; BDH) or oat-spelt xylan (Sigma) (25, 50 and 100 mg ml)1) and suspended in TRIS/HCl bu€er (50 mM, pH 7.0). After gentle shaking for 1 h at 5 °C, the samples were centrifuged at 7000 g for 10 min and the precipitate washed three times with TRIS/HCl bu€er. Enzyme bound to the polysaccharides was eluted with NaCl (2 M). Sodium dodecyl sulphate (SDS, 10% w/v) was also used to elute proteins, which were then heated to 70 °C for 15 min. All samples were centrifuged at 12 000 g for 10 min. Xylanase activity was recovered after the material had been dialysed against 2  1000 volumes of distilled water.

Enzyme puri®cation Xylanases were puri®ed by ultra®ltration, cation-exchange chromatography and binding to oat-spelt xylan. Chromatography was performed in a Pharmacia fast protein liquid chromatography system. The culture ®ltrate was concentrated ®vefold by ultra®ltration using a Bio¯ow (Bio-2000) cartridge (10 kDa). Portions (10 ml) of the concentrated ®ltrate were run on a CM-Biogel column …2:5  5 cm† previously equilibrated with phosphate buffer (10 mM, pH 7.0). Protein were then eluted with the same bu€er using a NaCl gradient (0±1 M) at a ¯ow rate of 1 ml min)1. Fractions (2 ml) were collected from the column and the elution of protein monitored at 280 nm. Fractions exhibiting xylanase activity were pooled, dialysed against phosphate bu€er (10 mM, pH 7.0), and mixed with oat-spelt xylan as describe above.

Electrophoretic analysis Slab-gel electrophoresis was carried out under denaturing conditions (SDS/polyacrylamide gel electrophoresis) according to Laemmli (1970) in 12% polyacrylamide in a Mini-protean II Bio-Rad system. Protein bands were made visible either by staining with silver nitrate (Morrisey 1981) or with Coomassie brilliant blue G250. A low-molecular-mass standard mixture (Pharmacia;14 400± 94 000 Da) was used to determine the apparent molecular masses of the samples. Xylanase activity was detected on zymogram gels as previously described (Copa-PatinÄo et al. 1993). Isoelectric focusing was carried out in a ``Mini IEF Cell'' Bio-Rad system with an isoelectric point range of 3.0±9.0.

Hydrolysis studies

Results and discussion Binding and removal of xylanases from Avicel and oat-spelt xylan The ability of the two commercially available insoluble polysaccharides, Avicel (microcrystalline cellulose) and oat-spelt xylan to bind xylanases was assessed. Culture supernatants from 96 h growth of S. chattanoogensis containing active xylanases (2.5 U mg)1) was used as the source of xylanases and, following binding, xylanases were removed using NaCl (2 M). Both oat-spelt xylan and Avicel were capable of binding xylanases; however, at least three-times more xylanase activity was bound and then successfully removed from oat-spelt xylan (data not shown). The concentration of oat-spelt xylan used (25±100 mg) did not a€ect the amount of enzyme activity recovered. In contrast, increasing the Avicel concentration resulted in increased xylanase recovery. This can be readily seen in Fig. 1, where the intensity of the zymogram stain for the enzyme increased at higher Avicel concentrations (100 mg). The results suggest that xylanases may be competing for binding sites on Avicel, but not on oat-spelt xylan, other proteins being present in lower concentrations than xylanase, but having a stronger anity to Avicel. No cellulase activity could be detected either in culture supernatants or in the bound enzyme, indicating not only that endoglucanases were absent in culture supernatants, but also that the bound enzyme exhibited only xylanase activity. Cellulosebinding domains in xylanases from Pseudomonas ¯uorescens and Thermomonospora fusca, which do not hydrolyse b1-4 glycosidic linkages, have been reported

286

Fig. 1A±D Sodium dodecyl sulphate/polyacrylamide gel electrophoresis and zymogram showing xylanase activity separated from oatspelt xylan (A, B) and Avicel (C, D). Both carbohydrates were used at 25 mg (1), 50 mg (2) and 100 mg (3)

well in excess of the single cation-exchange step, followed by oat-spelt xylan binding, which was employed in this study.

previously (Hall et al. 1989; Ferreira et al. 1990; and Irwin et al. 1994).

Properties of the puri®ed xylanase

Application of xylanases/oat-spelt xylan binding to rapid enzyme puri®cation One potential application for the binding of xylanases to oat-spelt xylan may be in the rapid puri®cation of xylanases. Using the puri®cation steps outlined in Table 1, xylanase activity was puri®ed almost 300-fold from an initial speci®c activity of 2.5 U mg)1 with a ®nal recovery of 17.7% of the total activity present. The ultra®ltration step resulted in an increased speci®c activity to 3.8 U mg)1. This increase in enzyme activity following ultra®ltration has been previously observed (CopaPatinÄo et al. 1993) and may be due to the removal of xylose oligomers, which inhibit endoxylanase activity during ultra®ltration. The speci®c activity of the puri®ed xylanase, 729.5 U mg)1, compares well with results of other work on the activity of puri®ed xylanases that report ®nal activities of 40 U mg)1 for a xylanase from a Bacillus sp. (Blanco et al. 1995), 580 U mg)1 for a xylanase from an alkalophilic actinomycete (Tsujibo et al. 1990) and between 300 U mg)1 and 1009 U mg)1 for three xylanases from S. lividans (Kluepfel et al. 1990, 1992). Further, many of the puri®cation protocols used required a number of column chromotography steps,

To assess the e€ect of the puri®cation protocol on the stabilities and activities of the xylanases, the puri®ed enzyme was characterized. The molecular mass of the enzyme, determined by SDS/polyacrylamide gel electrophoresis, was found to be 48 kDa with a higher degree of glycosylation (45%) than has been reported for other xylanases (Khasin et al.1993). The isoelectric point for the xylanase was estimated to be pH 9.0. Maximum enzyme activity occurred at pH 6.0, although the enzyme was stable for 1 h at a range of pH values from 5.0 to 8.0. Temperature studies revealed that, under our assay conditions, the puri®ed xylanase exhibited maximal activity at 50 °C Table 1 Puri®cation of CM-2 xylanase activity from Streptomyces chattanoogensis Puri®cation step

Total Total Yield activity protein (%) (U) (mg)

Supernatant 241.2 Ultra®ltration 327 CM-Biogel 151.8 chromatography Xylan bound 42.7

96.4 86.1 0.8 0.06

Speci®c Puri®cation activity factor (U/mg protein)

± 135 62.9

2.5 3.8 173.7

±

17.7

729.5

291.8

1.5 69.5

287

with no loss of activity detected after a 1-h incubation at temperatures up to 50 °C. The activities and stabilities of the xylanase (CM-2) are similar to those reported for other actinomycete xylanases, with pH stability around pH 5±8 and temperature stability between 40 °C and 60 °C (McCarthy 1987). Kinetic studies with the puri®ed xylanase at 50 °C, using oat-spelt and birchwood xylan, yielded Vmax values of 78.2 U mg)1 and 19.1 U mg)1 for the two substrates respectively. Km values were 4.0 mg ml)1 and 0.3 mg ml)1 respectively. The Km values reported here are similar to those published previously for other actinomycete xylanases (Kluepfel et al. 1992), although most studies report that puri®ed xylanases exhibit greater anity for birchwood than for oat-spelt xylan (Kimura et al. 1995). The study of the e€ect of di€erent metal ions and EDTA showed that a concentration of 1 mM Hg2+ completely inhibited xylanase activity. At similar metal concentrations, a reduction in activity of around 20% was observed when Cu+ and Ag+ was added, while the addition of Mn2+ stimulated xylanase activity by 40%. This result contrasts other reports in which Mn2+ addition resulted in inhibition of xylanase activity (Khasin et al. 1993). The addition of EDTA did not a€ect the activity. Analysis of the products from the degradation of oatspelt xylan con®rmed the enzyme to be an endoxylanase with xylobiose, xylotriose and xylotetrose the main degradation products. In conclusion, the application of anity binding for the puri®cation of xylanase activity from S. chattanoogensis resulted in the production of active xylanase activity with properties that suggest industrial potential for this enzyme and the puri®cation technique. We are currently evaluating the application of these techniques to industrial scale-up for xylanases production in the removal of hemicellulose from pulp paper. Acknowledgements This work has been supported by CICYT PROJECT BIO93-0662-C04-02 and the EC PROJECT AGRECT90-0047 (SMA) and was aided by a fellowship to C.L. LoÂpezFernaÂndez from Comunidad AutoÂnoma de Madrid, Spain.

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