Alkalistable endo-β-1,4-xylanase production from a newly isolated alkalitolerant Penicillium sp. SS1 using agro-residues

Abstract

Thermostable and alkalitolerant xylanases have got intense research focus due to their vast applications in various industries including pulp and paper, food, feed, textile, biofuel, etc. In the present investigation, a Penicillum sp. SS1 isolated from degrading woody material was found to produce moderately thermoactive and alkalistable endo-β-1,4-xylanase (xylanase). Maximum xylanase production was observed after fourth day of fermentation (43.84 IU/ml). The organism produced substantial quantities of xylanase using agricultural residues like wheat bran (20.6 IU/ml), rice bran (21.8 IU/ml) and sawdust (10.7 IU/ml) as carbon sources. The enzyme preparation was totally free of filter paper activity (FPase) and possessed negligible carboxymethyl cellulase (CMCase) activity; this could be an important feature of enzyme if the intended application of enzyme is in pulp and paper industries. Among nitrogen sources examined, yeast extract supported maximum xylanase production (45.74 IU/ml), and was followed by soybean meal (22.2 IU/ml) and ammonium sulphate (20 IU/ml). Maximum xylanase production was observed at initial medium pH 9 (25.6 IU/ml); however, at pH 8 and 10 also significantly high enzyme titre was observed (24 and 21.2 IU/ml, respectively). Thus, Penicillium sp. SS1 displayed capability of growing and producing xylanase at high alkaline pH (8-10). Maximum xylanase activity was reported at 50 °C, however, significantly high activity was observed at 60 °C (65.4%), however, at 70-80 °C activity was lost considerably. At 50-60 °C the enzyme retained very high activity up to 30-60 min (91-100%), however, prolonged incubation (90 min) caused considerable activity reduction (residual activity 63-68%).

Fig. 1

Growth and time-course of xylanase production by Penicillium sp. SS1. Fermentation was conducted in production medium under shaking (180 rpm) at 30 °C, and biomass and xylanase produced were assayed. Error bars show standard deviations

Fig. 2

Demonstration of inducible nature of Penicillum sp. SS1 xylanase on xylan agar plate by Congo red staining. Well-1 was loaded with cultural supernatant from medium with xylan as carbon source, well-2 was loaded with cultural supernatant from medium with glucose as carbon source. Arrow indicates zone of clearance

Fig. 3

Demonstration of endoxylanolytic nature of Penicilliumsp. SS1 xylanase.Lane 1 andlane 2 indicate standard xylose control and standard xylan control, respectively, while thelane 3 represents xylanase-treated xylan, showing the presence of xylan degradation products (xylose, xylobiose, xylotriose and xylooligosaccharides) due to action of xylanase on xylan

Fig. 4

Xylanase production by Penicillium sp. SS1 on agriculture-based carbon sources. Xylan of the production medium was replaced with either of the carbon source and fermentation was conducted (180 rpm) at 30 °C. Error bars indicate standard deviations

Fig. 5

Xylanase production by Penicillium sp. SS1 using different nitrogen sources. The usual nitrogen source of the production medium was replaced with either of the nitrogen source and fermentation was conducted. Error bars show standard deviations

Fig. 6

Effect of initial medium pH on xylanase production by Penicillium sp. SS1. pH of the production medium was adjusted with sodium carbonate (2%, w/v) and fermentation was conducted at 30 °C on shaker (180 rpm). Error bars show standard deviations

Fig. 7

Effect of pH on activity of Penicillium sp. SS1 xylanase. Xylanase assay was performed at different pH (3–10) using appropriate buffers. Error bars indicate standard deviations

Fig. 8

Effect of temperature on activity of Penicillium sp. SS1 xylanase. Xylanase assay was conducted at different temperatures (30–90 °C). Error bars show standard deviations

Fig. 9

Thermostability of xylanase from Penicillium sp. SS1. Enzyme was preincubated at different temperatures (50–90 °C) for varying time periods (30–90 min) and then assayed for residual activity. Error bars show standard deviations