A cell-factory model of Saccharomyces cerevisiae based on bacterial cellulose without GMO for consolidated bioprocessing of starch

In this study, an effort was made to create a model cell factory of Saccharomyces cerevisiae using bacterial cellulose (BC) and Aspergillus awamori for consolidated bioprocessing (CBP) of starch. This work suggested development of a cell factory for consolidated bioprocessing of starch in one bioreactor, performing three bioprocesses, i.e. production of amylolytic enzymes by fungal culture, hydrolysis of starch and fermentation to ethanol production using S. cerevisiae without its genetic modification. The microorganisms were separately immobilized on different amounts of BC and their mixture was used for the fermentation of 5% w/v starch. The mixture of BC/A. awamori and BC/S. cerevisiae was used for starch fermentation both in wet and freeze-dried (lyophilized) form in the same ratio (3:1). A 1.75-fold increase in maximum ethanol production was observed using freeze-dried BC immobilized biocatalysts compared to wet cell factory. The ethanol production yield was examined progressively by the effect of (i) initial ratios of both freeze-dried BC/S. cerevisiae and BC/A. awamori, (ii) different weight of the freeze-dried cell factory and (iii) A. awamori cells concentration, reaching the 82% of the theoretical yield encouraging us to use this cell factory model for further fermentations of starch in higher concentration. Ethanol production of 26.69 mL/L and the maximum ethanol yield (0.42 g ethanol/g starch) or 82% of the theoretical yield was achieved by increasing cells of A. awamori inoculum during its immobilization on BC to 109 cells/mL. The results of this work are satisfactory compared with other systems of starch fermentation from literature. SEM, TEM and FTIR spectra analysis were carried out in order to prove the successful preparation of cell factory. SEM showed the immobilization of cells on the BC netting, and TEM showed on BC fibrils. Finally, a repeated fermentation batch was performed, proving the operational viability and stability of the cell factory. The results indicated that the objective of designed cell factory was successfully performer, and the results of starch fermentation are promising for the development of an innovation in brewing industry. Likewise, these have prospects of their application in White-Biotechnology.