BioVT-2011-14 [BibTeX]
Gernot Jäger, Michele Girfoglio, Florian Dollo, Roberto Rinaldi, Hans Bongard, Ulrich Commandeur, Rainer Fischer, Antje Spieß, Jochen Büchs:
How recombinant swollenin from Kluyveromyces lactis affects cellulosic substrates and accelerates their hydrolysis
Biotechnology for Biofuels, 2011, 4(1), 33
Abstract:
Background: In order to generate biofuels, insoluble cellulosic substrates are
pretreated and subsequently hydrolyzed with cellulases. One way to pretreat
cellulose in a safe and environmentally friendly manner is to apply, under mild
conditions, non-hydrolyzing proteins such as swollenin - naturally produced in
low yields by the fungus Trichoderma reesei. To yield sufficient swollenin for
industrial applications, the first aim of this study is to present a new way of
producing recombinant swollenin. The main objective is to show how
swollenin quantitatively affects relevant physical properties of cellulosic
substrates and how it affects subsequent hydrolysis.
Results: After expression in the yeast Kluyveromyces lactis, the resulting
swollenin was purified. The adsorption parameters of the recombinant
swollenin onto cellulose were quantified for the first time and were comparable
to those of individual cellulases from T. reesei. Four different insoluble
cellulosic substrates were then pretreated with swollenin. At first, it could be
qualitatively shown by macroscopic evaluation and microscopy that swollenin
caused deagglomeration of bigger cellulose agglomerates as well as
dispersion of cellulose microfibrils (amorphogenesis). Afterwards, the effects
of swollenin on cellulose particle size, maximum cellulase adsorption and
cellulose crystallinity were quantified. The pretreatment with swollenin resulted
in a significant decrease in particle size of the cellulosic substrates as well as
in their crystallinity, thereby substantially increasing maximum cellulase
adsorption onto these substrates. Subsequently, the pretreated cellulosic
substrates were hydrolyzed with cellulases. Here, pretreatment of cellulosic
substrates with swollenin, even in non-saturating concentrations, significantly accelerated the hydrolysis. By correlating particle size and crystallinity of the
cellulosic substrates with initial hydrolysis rates, it could be shown that the
swollenin-induced reduction in particle size and crystallinity resulted in high
cellulose hydrolysis rates.
Conclusions: Recombinant swollenin can be easily produced with the robust
yeast K. lactis. Moreover, swollenin induces deagglomeration of cellulose
agglomerates as well as amorphogenesis (decrystallization). For the first time,
this study quantifies and elucidates in detail how swollenin affects different
cellulosic substrates and their hydrolysis.
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