Biotechnology, Department of Chemistry, Center for Chemistry & Chemical Engineering, Lund University, Lund, Sweden.
Laboratórios de Desenvolvimento de Bioprocessos, Departamento de Engenharia Bioquímica, Escola de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
J Appl Microbiol. 2018 Aug;125(2):480-489. doi: 10.1111/jam.13895. Epub 2018 May 31.
Immobilization of microbial cells is a useful strategy for developing high cell density bioreactors with improved stability and productivity for production of different chemicals. Functionalization of the immobilization matrix or biofilm forming property of some strains has been utilized for achieving cell attachment. The aim of the present study was to investigate the production of exopolysaccharide (EPS) by Propionibacterium freudenreichii C.I.P 59.32 and utilize this feature for immobilization of the cells on porous glass beads for production of propionic acid.
Propionibacterium freudenreichii was shown to produce both capsular and excreted EPS during batch cultivations using glucose as carbon source. Different electron microscopy techniques confirmed the secretion of EPS and formation of cellular aggregates. The excreted EPS was mainly composed of mannose and glucose in a 5·3 : 1 g g ratio. Immobilization of the cells on untreated and polyethyleneimine (PEI)-treated Poraver beads in a bioreactor was evaluated. Higher productivity and yield of propionic acid (0·566 g l h and 0·314 g g , respectively) was achieved using cells immobilized to untreated beads and EPS production reached 617·5 mg l after 48 h.
These results suggest an important role of EPS-producing strains for improving cell immobilization and propionic acid production.
This study demonstrates the EPS-producing microbe to be easily immobilized on a solid matrix and to be used in a bioprocess. Such a system could be optimized for achieving high cell density in fermentations without the need for functionalization of the matrix.
微生物细胞的固定化是开发高细胞密度生物反应器的一种有效策略，可提高生产不同化学品的稳定性和生产力。已经利用固定化基质的功能化或某些菌株的生物膜形成特性来实现细胞附着。本研究的目的是研究丙酸弗雷登斯氏菌 C.I.P 59.32 生产胞外多糖 (EPS)，并利用这一特性将细胞固定在多孔玻璃珠上生产丙酸。
在使用葡萄糖作为碳源的分批培养中，显示丙酸弗雷登斯氏菌同时产生荚膜和分泌 EPS。不同的电子显微镜技术证实了 EPS 的分泌和细胞聚集体的形成。分泌的 EPS 主要由甘露糖和葡萄糖组成，比例为 5·3：1 g/g。在生物反应器中评估了未处理和聚乙烯亚胺 (PEI) 处理的 Poraver 珠上细胞的固定化。使用未处理珠上固定化的细胞，可实现更高的丙酸生产力和产率（分别为 0·566 g l h 和 0·314 g g），并且在 48 h 后 EPS 产量达到 617.5 mg l。
这些结果表明 EPS 产生菌在改善细胞固定化和丙酸生产方面具有重要作用。
本研究表明 EPS 产生菌可轻易固定在固体基质上，并可用于生物过程。这样的系统可以在不需要基质功能化的情况下进行优化，以实现发酵中的高细胞密度。
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