Optimization of Aspergillus fijiensis β-fructofuranosidase expression and production using Pichia pastoris, for the production of fructooligosaccharides from sucrose

Coetzee, Gerhardt (2019-04)

Thesis (PhD)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: The South African sugar industry faces challenges affecting its profitability such as low international market price and the implementation of tax legislation by the South African National Treasury on sugar-sweetened beverages (SSBs). To alleviate these effects, the industry could produce alternative high-value, low-calorie products from sucrose such as short-chain fructooligosaccharides (scFOS). This product diversification may increase the industry’s revenue while addressing the sugar tax legislation. In this study, the β-fructofuranosidase from Aspergillus fijiensis ATCC 20611 was selected to produce scFOS from sucrose. Native (fopA) and protein-engineered (fopA_V1) versions of the enzymes were produced recombinantly in Pichia pastoris. Factors influencing heterologous protein production require empiric evaluation for each protein and thus the aim was to optimize the yeast expression system and cultivation processes to maximize β-fructofuranosidase production. On the genetic level, different yeast strains, promoters and gene codon-optimization techniques were compared. Dissolved oxygen controlled (DO-stat) and constant feeding strategies were compared in bioreactor cultivations to investigate the influence of yeast growth on volumetric enzyme titers. The application of the two enzymes to produce scFOS from industrial sugar streams were optimized using response surface methodology (RSM). In shake flask experiments the P. pastoris DSMZ 70382 strain proved superior to X-33 when expressing Geneart® codon-optimized fopA under control of the AOX1 and GAP promoters (12.1 U/ml and 3.2 U/ml for AOX1 and 12.0 U/ml and 11.3 U/ml for GAP, respectively). Further bioreactor studies with P. pastoris DSMZ 70382 native fopA transformants showed that the AOX1 promoter was superior to GAP while ATUM codon-optimization produced higher titers than Geneart® (13 702 U/ml and 2 718 U/ml for AOX1 and 6 057 U/ml and 1 790 U/ml for GAP, respectively). Constant feed cultivations produced higher growth rates for strains expressing the ATUM genes under the GAP promoter, but lower volumetric enzyme activities compared to DO-stat cultivations (2 129.25 and 1686.91 U/ml for GAPfopA and GAPfopA_V1, respectively, with DO-stat and 1413.36 and 1222.70 U/ml for GAPfopA and GAPfopA_V1, respectively, with constant feed). The GAPfopA strain produced higher enzyme activities than the GAPfopA_V1 for the constant feed and DO-stat method. Due to the shorter cultivation time, the constant feed method exhibited higher volumetric productivity for both strains (23.96 x 103 and 20.72 x 103 U/L/h for GAPfopA and GAPfopA_V1, respectively). In scFOS production, the native and engineered enzymes were compared to evaluate whether the protein engineering afforded advantages in enzyme performance on non-ideal substrates (industrial sugar). RSM indicated optimum conditions to produce a target scFOS composition were 62 ⁰C and 10 U/g sucrose using pure sugar. These conditions were applied to A-molasses and refinery molasses, however the desired scFOS composition was only successfully attained using A-molasses. In conclusion, P. pastoris proved to be a suitable host for the high-level expression and production of functional codon-optimized native (GAPfopA) and engineered (GAPfopA_V1) versions of the fopA enzyme and that these enzymes can be applied for the batch production of scFOS from a selection of industrial sugar streams for the purpose of reducing process cost.

AFRIKAANSE OPSOMMING: Die Suid-Afrikaanse suikerindustrie staar uitdagings in die gesig wat winsgewendheid affekteer, soos lae internasionale markprys en die implementasie van belastingwetgewing deur die Suid-Afrikaanse Nasionale Tesourie op suikerversoete drankies (SSBs). Om hierdie gevolge te verlig, kan die industrie alternatiewe hoë-waarde, lae-kalorie produkte vervaardig uit sukrose soos kort-ketting frukto-oligosakkariede (scFOS). Hierdie produkdiversifikasie kan die industrie se inkomste verhoog terwyl die suikerbelastingwetgewing aangespreek word. In hierdie studie is die β-fruktofuranosidase van Aspergillus fijiensis ATCC 20611 gekies om scFOS uit sukrose te vervaardig. Natuurlike (fopA) en proteïen-gemanipuleerde (fopA_V1) weergawes van die ensiemes is rekombinant vervaardig in Pichia pastoris. Faktore wat die heteroloë proteïen vervaardiging beïnvloed, vereis empiriese evaluasie vir elke proteïen. Die doel was dus om die gis uitdrukkingsisteem en kultiveringsprosesse te optimeer om β-fruktofuranosidase te maksimeer. Op die genetiese vlak, is verskillende gislyne, promotors en geenkodonoptimeringstegnieke vergelyk. Opgeloste suurstof beheerde (DO-stat) strategië en konstante voerstrategië is vergelyk in bioreaktor kultiverings om die invloed van gisgroei op volumetriese ensieme titers te ondersoek. Die toepassing van die twee ensiemes om scFOS van industriële suikerstrome te vervaardig, is geoptimeer deur respons oppervlak metodologie (RSM) te gebruik. In skudfles eksperimente was die P. pastoris DSMZ 70382-lyn superieur bo die X-33 as GeneArt® kodon-geoptimeerde fopA onder beheer van die AOXI- en GAP- promotors (12.1 U/ml en 3.2 U/ml vir AOXI en 12.0 U/ml en 11.3 U/ml vir GAP, onderskeidelik) uitgedruk is. Verdere bioreaktorstudies met P. pastoris DSMZ 70382 natuurlike fopA tranformante het gewys dat die AOXI-promotor superieur was bo GAP terwyl ATUM-kodonoptimering hoër titers as GeneArt® gelewer het (13 702 U/ml en 2 718 U/ml vir AOX1 en 6 057 U/ml en 1 790 U/ml vir GAP, onderskeidelik). Konstante voerkwekings het hoër groeitempo’s gegenereer vir lyne wat die ATUM-gene onder die GAP-promotor uitgedruk het, maar laer volumetriese ensiemaktiwiteite in vergelyking met DO-stat-kwekings (2 129.25 U/ml en 1686.91 U/ml vir GAPfopA en GAPfopA_V1, onderskeidelik, met DO-stat en 1413.36 en 1222.70 U/ml vir GAPfopA en GAPfopA_V1, onderskeidelik, met konstante voer). Die GAPfopA-lyn het hoër ensiemaktiwiteite gegenereer as die GAPfopA_V1 vir die konstante voer en DO-stat metode. As gevolg van die korter kwekingstyd, het die konstante voer metode hoër volumetriese produktiwiteit vir beide lyne vertoon (23.96 x 103 en 20.72 x 103 U/L/h vir GAPfopA en GAPfopA_V1, onderskeidelik). In scFOS vervaardiging, is die natuurlike en gemanipuleerde ensiemes vergelyk om te evalueer of die proteïen-manipulering voordele in ensiemdoeltreffendheid op nie-ideale substrate (industriële suiker) oplewer. RSM het aangedui dat optimum kondisies om ’n doelwit scFOS-samestelling te vervaardig is 62 °C en 10 U/g sukrose wat suiwer suiker gebruik. Hierdie kondisies is toegepas op A-molasse en geraffineerde molasse, alhoewel die gewenste scFOS-samestelling slegs suksesvol verkry is deur A-molasse te gebruik. Ter afsluiting, P. pastoris is bewys as ’n gepaste draer vir die hoë-vlak uitdrukking en produksie van funksionele kodon-geoptimeerde natuurlike (GAPfopA) en gemanipuleerde (GAPfopA-V1) weergawes van die fopA-ensiem en dat hierdie ensiemes toegepas kan word op die lotproduksie van scFOS van ’n deel van industriële suikerstrome met die doel om proseskostes te verminder.

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