# Membrane Lipids and Osmolytes Rearrangements Under Cell Wall Stress in Aspergillus niger

## TL;DR

This study explores how Aspergillus niger responds to cell wall stress by examining changes in membrane lipids and osmolytes.

## Contribution

The study reveals that minor lipid and osmolyte changes do not support their role in adapting to cell wall stress in A. niger.

## Key findings

- CWS in A. niger leads to hyphal swelling and increased chitin and glucan in the cell wall.
- Glycerol levels decrease under CWS, but membrane and storage lipid amounts remain unchanged.
- Phospholipid unsaturation increases due to higher linolenic acid, possibly affecting membrane fluidity.

## Abstract

The cell wall integrity pathway is activated in response to cell wall stress (CWS). The defense system in aspergilli employs three transcription factors—RlmA, MsnA, and CrzA—which also facilitate adaptation to various abiotic stressors and involve alterations in cytosolic osmolyte composition and membrane lipid profiles. However, their role in adaptation to CWS remains unclear. In Aspergillus niger, CWS induced by Congo red and calcofluor white caused a pronounced cessation of apical growth, accompanied by hyphal globular swelling and an increase in chitin and glucan content in the cell wall. Regarding the osmolyte composition, which predominantly consists of low levels of glycerol and mannitol, glycerol levels were reduced under CWS. Neither the composition nor the amounts of membrane and storage lipids changed following CWS; however, the degree of unsaturation of phospholipids increased due to a higher proportion of linolenic acid, potentially enhancing membrane fluidity. These minor rearrangements of membrane lipids and osmolytes do not confirm their involvement in the adaptation to CWS induced by Congo red and calcofluor white, contrary to previous assumptions based on studies of cell wall integrity pathways.