Neochloris oleoabundans cell walls have an altered composition when cultivated under different growing conditions

Abstract

The impact that environmental factors have on the intracellular components of microalgae has been the focus of research for a number of decades. Despite that, their effects on the cell wall have received very little attention. In this study, we investigated how different growing conditions affect the cell walls of N. oleoabundans. The results revealed that the cell wall composition varied in that the modifications were different in the four cultivation media: freshwater nitrogen-replete (optimum culture) and -depleted conditions, and seawater nitrogen-replete and -depleted conditions. Nitrogen deficiency in freshwater cultivation was the only condition that significantly (p < .05) increased the total content of carbohydrates in the cell wall. The three most abundant components of freshwater-cultivated cell wall polysaccharides were rhamnose, galactose and glucuronic acid whereas in seawater media the main components of cell wall polysaccharides were rhamnose, glucose and galactose. The combined results of the biochemical analyses and monoclonal antibodies epitope-binding revealed that N. oleoabundans cell walls are likely composed of sulphated polysaccharides enriched in mannose, β-(1 → 4)-d-mannans, and glucose as they grow in seawater. Salinity and nitrogen deficiency also had an impact on the nitrogenous components of the cell wall. Under these conditions we observed a decrease in glucosamine in the cell wall. The analysis of specific binding of monoclonal antibodies, revealed that the cell wall of N. oleoabundans is possibly enriched in arabinogalactan proteins (AGPs). Under salinity and nitrogen deficiency N. oleoabundans increased the proportion of the non-polar to polar amino acids in the cell walls. An increase of leucine in the cell walls may suggest that N. oleoabundans contains leucine-rich repeat proteins which are known to play a vital role in stress responses. This report provides new insights into microalgae cell wall biology and how cell walls are remodelled when growing under different conditions.