Fructooligosaccharides production by immobilized Pichia pastoris cells expressing Schedonorus arundinaceus sucrose:sucrose 1-fructosyltransferase.

Fructooligosaccharides (FOSs)-fructose-based oligosaccharides-are typical prebiotics with health-promoting effects in humans and animals. The trisaccharide 1-kestotriose is the most attractive inulin-type FOS. We previously reported a recombinant sucrose:sucrose 1-fructosyltransferase (1-SST, EC 2.4.1.99) from Schedonorus arundinaceus (Sa) that efficiently converts sucrose into 1-kestotriose. In this study, Pichia pastoris PGFT6x-308 constitutively expressing nine copies of the Sa1-SST gene displayed fructosyltransferase activity in undisrupted biomass (49.8 U/ml) and culture supernatant (120.7 U/ml) in fed-batch fermentation (72 hr) with sugarcane molasses. Toluene permeabilization increased 2.3-fold the Sa1-SSTrec activity of whole cells entrapped in calcium-alginate beads. The reaction with refined or raw sugar (600 g/l) yielded 1-kestotriose and 1,1-kestotetraose in a ratio of 8:2 with their sum representing above 55% (wt/wt) of total carbohydrates. The FOSs yield decreased to 45% (wt/wt) when sugarcane syrup and molasses were used as cheaper sucrose sources. The beads retained 80% residual Sa1-SSTrec activity after a 30-day batchwise operation with refined cane sugar at 30°C and pH 5.5. The immobilized biocatalyst is attractive for the continuous production of short-chain FOSs, most particularly 1-kestotriose.

Removal of bacterial dextran in sugarcane juice by Talaromyces minioluteus dextranase expressed constitutively in Pichia pastoris.

A gene construct encoding the mature region of Talaromyces minioluteus dextranase (EC 3.2.1.11) fused to the Saccharomyces cerevisiae SUC2 signal sequence was expressed in Pichia pastoris under the constitutive glyceraldehyde 3-phosphate dehydrogenase promoter (pGAP). The increase of the transgene dosage from one to two and four copies enhanced proportionally the extracellular yield of the recombinant enzyme (r-TmDEX) without inhibiting cell growth. The volumetric productivity of the four-copy clone in fed batch fermentation (51 h) using molasses as carbon source was 1706 U/L/h. The secreted N-glycosylated r-TmDEX was optimally active at pH 4.5-5.5 and temperature 50-60 °C. The addition of sucrose (600 g/L) as a stabilizer retained intact the r-TmDEX activity after 1-h incubation at 50-60 °C and pH 5.5. Bacterial dextran in deteriorated sugarcane juice was completely removed by applying a crude preparation of secreted r-TmDEX. The high yield of r-TmDEX in methanol-free cultures and the low cost of the fed batch fermentation make the P. pastoris pGAP-based expression system appropriate for the large scale production of dextranase and its use for dextran removal at sugar mills.

Fructooligosaccharides production by Schedonorus arundinaceus sucrose:sucrose 1-fructosyltransferase constitutively expressed to high levels in Pichia pastoris.

The non-saccharolytic yeast Pichia pastoris was engineered to express constitutively the mature region of sucrose:sucrose 1-fructosyltransferase (1-SST, EC 2.4.1.99) from Tall fescue (Schedonorus arundinaceus). The increase of the transgene dosage from one to nine copies enhanced 7.9-fold the recombinant enzyme (Sa1-SSTrec) yield without causing cell toxicity. Secretion driven by the Saccharomyces cerevisiae α-factor signal peptide resulted in periplasmic retention (38%) and extracellular release (62%) of Sa1-SSTrec to an overall activity of 102.1 U/ml when biomass reached (106 g/l, dry weight) in fed-batch fermentation using cane sugar for cell growth. The volumetric productivity of the nine-copy clone PGFT6x-308 at the end of fermentation (72 h) was 1422.2 U/l/h. Sa1-SSTrec purified from the culture supernatant was a monomeric glycoprotein optimally active at pH 5.0-6.0 and 45-50 °C. The removal of N-linked oligosaccharides by Endo Hf treatment decreased the enzyme stability but had no effect on the substrate and product specificities. Sa1-SSTrec converted sucrose (600 g/l) into 1-kestose (GF2) and nystose (GF3) in a ratio 9:1 with their sum representing 55-60% (w/w) of the total carbohydrates in the reaction mixture. Variations in the sucrose (100-800 g/l) or enzyme (1.5-15 units per gram of substrate) concentrations kept unaltered the product profile. Sa1-SSTrec is an attractive candidate enzyme for the industrial production of short-chain fructooligosaccharides, most particularly 1-kestose.

Scaling-up batch conditions for efficient sucrose hydrolysis catalyzed by an immobilized recombinant Pichia pastoris cells in a stirrer tank reactor

Background: Invert sugar is used greatly in food and pharmaceutical industries. This paper describes scaling-up batch conditions for sucrose inversion catalyzed by the recombinant Pichia pastoris BfrA4X whole cells expressing Thermotoga maritima invertase entrapped in calcium alginate beads. For the first time, we describe the application of a kinetic model to predict the fractional conversion expected during sucrose hydrolysis reaction in both, a model and a prototype bioreactor with 0.5- and 5-L working volume, respectively. Results: Different scaled-up criteria used to operate the 0.5-L bioreactor were analyzed to explore the invert sugar large scale production. After model inversion studies, a 5-L scaled-up reaction system was performed in a 7-L stirred reactor. Both scaled-up criteria, immobilized biocatalyst dosage and stirring speed, were analyzed in each type of bioreactors and the collected data were used to ensure an efficient scale-up of this biocatalyst. Conclusions: To date, there is not enough information to describe the large-scale production of invert sugar using different scaled-up criteria such as dose of immobilized biocatalyst and stirring speed effect on mass transfer. The present study results constitute a valuable tool to successfully carry out this type of high-scale operation for industrial purposes.

Complete sucrose hydrolysis by heat-killed recombinant Pichia pastoris cells entrapped in calcium alginate.

BACKGROUND: An ideal immobilized biocatalyst for the industrial-scale production of invert sugar should stably operate at elevated temperatures (60-70°C) and high sucrose concentrations (above 60%, w/v). Commercial invertase from the yeast Saccharomyces cerevisiae is thermolabile and suffers from substrate inhibition. Thermotoga maritima ß-fructosidase (BfrA) is the most thermoactive and thermostable sucrose-hydrolysing enzyme so far identified and allows complete inversion of the substrate in highly concentrated solutions. RESULTS: In this study, heat-killed Pichia pastoris cells bearing N-glycosylated BfrA in the periplasmic space were entrapped in calcium alginate beads. The immobilized recombinant yeast showed maximal sucrose hydrolysis at pH 5-7 and 90°C. BfrA was 65% active at 60°C and had no activity loss after incubation without the substrate at this temperature for 15 h. Complete inversion of cane sugar (2.04 M) at 60°C was achieved in batchwise and continuous operation with respective productivities of 4.37 and 0.88 gram of substrate hydrolysed per gram of dry beads per hour. The half-life values of the biocatalyst were 14 and 20 days when operated at 60°C in the stirred tank and the fixed-bed column, respectively. The reaction with non-viable cells prevented the occurrence of sucrose fermentation and the formation of by-products. Six-month storage of the biocatalyst in 1.46 M sucrose (pH 5.5) at 4°C caused no reduction of the invertase activity. CONCLUSIONS: The features of the novel thermostable biocatalyst developed in this study are more attractive than those of immobilized S. cerevisiae cells for application in the enzymatic manufacture of inverted sugar syrup in batch and fixed-bed reactors.