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 con 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. coil 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. (c) 2015, The Society for Biotechnology, Japan. All rights reserved.