Combining AFM, XPS and chemical hydrolysis to understand the complexity and dynamics of C. vulgaris cell wall composition and architecture

The microalgae cell wall represents its interface with its environment and a strong barrier to disrupt in order to extract the cells products. Understanding its composition and architecture is a challenge that if overcome, could lead to substantial advancements in optimizing microalgae-production systems. However, the cell wall is a dynamic and complex structure that evolves depending on the growth phase or culture conditions. To apprehend this complexity, an experimental approach combining AFM, XPS, and chemical hydrolysis followed by HPAEC-PAD was developed to understand the cell wall of Chlorella vulgaris, a biotechnologically-relevant green microalgae species. Exponential and stationary growth stages were investigated, as well as saline stress condition inducing lipid production. Results showed that both the cell wall composition and architecture changes in stationary phase, with an increase of the lipidic fraction at the expanse of the proteic fraction, changes in the polysaccharidic composition, and a significant increase of its rigidity. Under saline stress, cell wall architecture seems to be affected as its rigidity decreases importantly. Altogether, this study demonstrates the power of combining these three techniques to give new insights into C. vulgaris cell wall, in terms of composition and architecture, and of its dynamics in different conditions.