Detailed biochemical and morphologic characteristics of the green microalga Neochloris oleoabundans cell wall

Abstract

Chlorophyta, the group of green algae of which there are >6000 species, manifests a great diversity of intercellular and extracellular components. Building blocks in the cell walls of Chlorophyta are very distinct and they may contain various components. Here, we characterize the cell walls of Neochloris oleoabundans, a Chlorophyte microalga, both in terms of biochemical composition and morphology. N. oleoabundans cell walls are composed of about 24.3% carbohydrates, 31.5% proteins, 22.2% lipids and 7.8% inorganic material, which contrasts to the cell walls of (higher) terrestrial plants in which carbohydrates are by far the main component. We also observed that cell wall carbohydrates are mainly non-cellulosic polysaccharides, essentially composed of rhamnose, galactose, glucuronic acid and glucosamine, of which glucose is only a minor component. The lipids comprising the N. oleoabundans cell walls are generally wax/cutin-like. Electron microscopic studies revealed that N. oleabundans cell walls are approximately 200 nm thick and consist of two main layers: a thinner inner layer and a more electron-dense outer layer. On the outer layer are hair-like structures that are possibly rich in carbohydrates. These findings are an important contribution that enable us to understand the complexity of cell walls in green microalgae.