The high viscosity of fermentation broth limited the further improvement of PGA titer. Our previous studies indicated that adding KCl to the medium could decrease the fermentation broth viscosity and improve the PGA titer. In order to clarify the reason, effects of cell physiological structure on the fermentation broth viscosity were investigated. Results from cell morphology observation showed that the reduction of cell aggregation caused by the weakened cross-linking between PGA and cells might be an important reason for the decrease in the fermentation broth viscosity. Besides, when 201.2 mM KCl was added to the medium, the zeta potential of cell surface decreased from - 70.48 ± 3.35 mV to - 81 ± 2.46 mV. The cell membrane integrity was reduced and permeability was enhanced. Furthermore, the percentage of lauric acid C12:0 in cell membrane increased by 12.36%, but palmitic acid C16:0 and stearic acid C18:0 decreased by 6.83% and 5.64%, respectively, which improved the fluidity of cell membrane. The above changes in cell membrane further affect the cross-linking between PGA and cells, thereby playing an important role in reducing the fermentation broth viscosity. This study provided some novel information for understanding the decrease of PGA fermentation broth viscosity by KCl.

中文翻译：

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细胞生理结构对枯草芽孢杆菌GXA-28生产聚γ-谷氨酸过程中发酵液粘度的影响。

发酵液的高粘度限制了PGA滴度的进一步提高。我们以前的研究表明，向培养基中添加KCl可以降低发酵液的粘度并提高PGA滴度。为了阐明原因，研究了细胞生理结构对发酵液粘度的影响。细胞形态学观察结果表明，由于PGA与细胞之间的交联减弱而导致的细胞聚集减少可能是发酵液粘度降低的重要原因。此外，当将201.2mM KCl添加到培养基中时，细胞表面的ζ电势从-70.48±3.35mV降低至-81±2.46mV。细胞膜完整性降低，通透性提高。此外，月桂酸C12的百分比：细胞膜中的0增加了12.36％，而棕榈酸C16：0和硬脂酸C18：0分别减少了6.83％和5.64％，这改善了细胞膜的流动性。细胞膜的上述变化进一步影响了PGA和细胞之间的交联，从而在降低发酵液粘度中起重要作用。这项研究为理解KCl降低PGA发酵液粘度提供了一些新颖的信息。