L-threonine is one of the most important amino acids in the human body, and because of its large use in the food, chemical and pharmaceutical industries, its demand is sharply growing. At present, microbial fermentation with Escherichia coli as the best candidate strain is widely used for industrial production of L-threonine. L-threonine fermentation, however has been carried out in a free-cell batch fermentation mode, in which cells can not be reused after fermentation. This fermentation of the batch and the single use of cells will increase operating costs and reduce productivity. Meanwhile, stress conditions such as shear forces during aerobic fermentation frequently threaten the free cells distributed in fermentation media, resulting in decreased cell viability over the fermentation phase. To increase fermentation efficiency, these problems need to be solved urgently.
These finding were publish in Frontiers in Microbiology under title " Efficient Biofilm-Based Fermentation Strategies for L-Threonine Production by Escherichia coli".
Explain by author " we have engineered E. Coli by overexpressing the gene fimH, which under industrial aerobic cultivation conditions successfully enhanced its biofilm formation. Subsequently, an immobilised fermentation strategy based on biofilm was created. During batch fermentations, L-threonine production increased from 10.5 to 14.1 g/L and further to 17.5 g/L with increased productivity during continuous (repeated-batch) fermentations.
Transcriptome research has also studied the molecular basis for enhanced biofilm formation and L-threonine biosynthesis. This research goes beyond traditional studies based on the pathogenic elements of E. Coli biofilm and represents a good case of engineered this bacteria.
PCR and sequencing findings verified the successful construction of recombinant strains in which the fimH gene was overexpressed (E. coli W1688-fimH*) or knocked out (E. coli W1688-fimH). The experiment with 96-well plates showed that these strains' biofilm forming skills were distinct.
Optical density for E.coli W1688-fimH* from crystal violet staining (which was the biofilm quantity indicator). In LB medium, the expression increased dramatically by 75.9 percent compared with that of the original strain (1.34 vs. 2.35), which could be due to fimH gene overexpression. Conversely, the optical density of E.coli due to the deletion of the fimH gene, was reduced by 388% (1.34 vs. 0.82).
In addition, SEM and fluorescence microscope images showed that in E.coli W1688-fimH the formation of biofilm and cell adhesion is more apparent. Compared with the initial strain, E. coli. In E. coli Apparently, biofilm formation was reduced and a sparse bacterial distribution was observed.
Taken together these findings showed that fimH gene overexpression promoted cell adhesion to abiotic surfaces and led to the effects of clustering resulting in the formation of biofilms. In comparison, the removal of the fimH gene had a detrimental impact on the development of biofilms. So there was a major regulatory impact of the fimH gene on E. coli Biofilm formation.