Response of Fe–S cluster assembly machinery of Escherichia coli to mechanical stress in a model of amino-acid crystal fermentation

During amino-acid crystal fermentation, mechanical stress on bacterial cells caused by crystal collision often impacts negatively on bacterial growth and amino-acid production. When Escherichia coli cells were cultivated under mechanical stress of polyvinyl chloride particles as a model of the crystal fermentation, activities of iron–sulfur (Fe–S) cluster-containing enzymes were apparently decreased. Based on an assumption that function of Fe–S cluster assembly machinery would be elevated to recover the enzyme activities in such stressed cells, we analyzed levels of various components of Fe–S cluster assembly machinery by western blotting. It was found that the expression of HscA, a chaperon component of the machinery, was up-regulated and that shorter forms of HscA with the N-terminal region truncated were accumulated, suggesting an important role of HscA against the mechanical stress. An overexpression of HscA gene in E. coli cells gave a positive effect on rescue of the stress-induced decrease of the activity of Fe–S cluster-containing enzyme. These results may provide a new strategy to alleviate the mechanical stress during the amino-acid crystal fermentation.