Insights into the role of cyclopropane fatty acid synthase (CfaS) from extreme acidophile in bacterial defense against environmental acid stress

The cell membrane remodeling mediated by cyclopropane fatty acid synthase (CfaS) plays a crucial role in microbial physiological processes resisting various environmental stressors, including acid. Herein, we found a relatively high proportion (24.8%-28.3%) of cyclopropane fatty acid (CFA) Cy-19:0 in the cell membrane of a newly isolated extreme acidophile, Acidithiobacillus caldus CCTCC AB 2019256, under extreme acid stress. Overexpression of the CfaS encoding gene cfaS2 in Escherichia coli conferred enhanced acid resistance. GC–MS analysis revealed a 3.52-fold increase in the relative proportion of Cy-19:0 in the cell membrane of the overexpression strain compared to the control. Correspondingly, membrane fluidity, permeability and cell surface hydrophobicity were reduced to varying degrees. Additionally, HPLC analysis indicated that the overexpression strain had 1.54-, 1.42-, 1.85-, 1.20- and 1.05-fold higher levels of intracellular glutamic acid, arginine, aspartic acid, methionine and alanine, respectively, compared to the control. Overall, our findings shed light on the role of CfaS derived from extreme acidophile in bacterial defense against environmental acid stress, potentially facilitating its application in the design and development of industrial microbial chassis cells for organic acid production.