Response of Psychrotolerant Fungus Mucor flavus to Cell Wall Stress, Induced by Azo Dyes.

The cell wall (CW) of Mucoromycota has a unique chitin/chitosan complex, unlike chitin/glucan complex in Ascomycota. Under cell wall stress (CWS), induced by azo dyes, ascomycetes increase the amount of CW chitin. This study analyzes the response of Mucor flavus to CWS, induced by Congo red and Calcofluor white. It was found that azo dyes significantly reduced the biomass yield and inhibited apical growth and branching but did not lead to an increase in the amount of CW chitin/chitosan, neutral polysacchrides and cytosol osmolytes. Non-bilayer phosphatidic acids and phosphatidylethanolamines dominated in the control membrane lipids, but the proportion of bilayer phosphatidylcholines did not exceed 5%. Under CWS, the proportion of phosphatidic acids increased, while the proportion of phosphatidylethanolamines decreased and the degree of unsaturation of phospholipids increased. Storage lipids in the control were represented by mono-, di- and triacylglycerides and free fatty acids. Under CWS, the proportion of diacylglycerides increased significantly, while the proportion of triacylglycerides decreased. Thus, the CWS response of M. flavus consisted of significant changes in growth and the composition of membrane and storage lipids, but the amount of CW chitin/chitosan and cytosol osmolytes did not increase, which is different from the response of ascomycetes.