A cell-factory model of Saccharomyces cereuisiae 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 cereuisiae 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. cereuisiae 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. cereuisiae 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. cereuisiae 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 10(9) 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. (C) 2021 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Automated summary

This study successfully created a model cell factory using bacterial cellulose and Aspergillus awamori for consolidated bioprocessing of starch, resulting in increased ethanol production and yield. The operational viability and stability of the cell factory were demonstrated through repeated fermentation batches. The results are promising for the development of innovation in the brewing industry and potential application in White-Biotechnology.