Kinetics of Xylanase Fermentation by Recombinant &lt;i&gt;Escherichia coli&lt;/i&gt; DH5α in Shake Flask Culture

Rusli Rusli

doi:10.3844/ajbbsp.2009.109.117

Abstract

Problem statement: Interest in xylanase enzyme application has markedly increased in pulp and paper processing industries. The switch to xylanase-producing recombinant Escherichia coli DH5α pTP510 is seen here as an economic alternative towards higher productivity and easier downstream purification. Modeling of E. coli DH5α growth and enzyme secretion is thus desired for future optimization in fermentation process. Approach: Kinetics of intracellular xylanase fermentation by a recombinant E. coli DH5α was studied in shake flask culture. The effect of different medium formulations (complex, minimal and defined), initial pH (6.5, 7.0, 7.4 and 8.0) and agitation speeds (150, 200 and 250 rpm) on cell growth and xylanase production were evaluated. Mathematical models based on Logistic and Luedeking-Piret equations had been proposed to describe the microbial growth and xylanase production. Results: Highest xylanase production was obtained in defined medium. Based on medium formulation, the highest cell concentration (4.59 g L-1) and xylanase production (2, 122.5 U mL-1) was obtained when (NH4)2HPO4 was used as the main nitrogen source, with an adjustment of the initial pH to 7.4 and agitation speed of 200 rpm. The maximum specific growth rate (µmax), growth associated xylanase production coefficient (α) and non-growth associated xylanase production coefficient (β) was 0.41 h-1, 474.26 U mg cell-1and 0 U mg cell-1 h-1, respectively. Conclusion: Xylanase production was growth associated process and the enzyme secretion was greatly dependent on cell concentration and the specific growth rate of E. coli DH5α.

Highlights

The polysaccharides of xylan typically associated with cellulose and lignins play an important structurally-supportive role in building up of plant cell walls[1]
Results from this study indicated that the type of nitrogen source was the important factor that determined growth rate of E. coli DH5α and xylanase production
It was found that the xylanase production was associated to growth of E. coli DH5α and xylanase production was proportionally increased with cell biomass

Summary

Introduction

The polysaccharides of xylan typically associated with cellulose and lignins play an important structurally-supportive role in building up of plant cell walls[1]. Degradation of hemicellulose component which mainly consists of xylan requires an efficient xylanolytic enzymatic systems; consisting several enzymes including endo-β-1,4-xylanase, β-xylosidase, α-L-arabinofuranosidase, α-glucuronidase, acetyl xylan esterase, ferulic acid esterase and p-coumaric acid esterase. There has been an increasing interest in xylanase enzyme fermentations regarding their wide applications in various industries, especially in paper and pulp industry. The use of xylanases and side-chain splitting enzymes in pulp bleaching, especially at higher temperature, helps to improve specific indicators, like kappa number and brightness. Filamentous fungi such as Aspergillus spp. and Trichoderma spp. are well known producers of extracellular xylanases[2]. Thermostable xylanase enzymes were secreted by some bacterial species such as Bacillus stearothermophilus[3] and Bacillus subtilis[4]. The ability of Penicillium purpurogenum (yeast) to produce several xylanases has been reported[5]

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Discussion

Conclusion