Cell wall modification of the green algae Scenedesmus sp.

Abstract

Scenedesmus is one of the most common freshwater algae genera. It can exist as unicellular organism; however, it is also found in coenobia organization which consists of four or eight cells inside a parental mother wall. The structure of the cell wall is important because it not only shapes the cell, but it is also the structure that is in contact with the external environment. In particular, Scenedesmus has a three-layered cell wall with cellulose, algaenan and pectin. In this work we generated transgenic algae overexpressing carbohydrate binding modules in the cell wall. The transgenic lines obtained are larger than wild type, their surface-to-volume ratio is affected, and the large mass promotes sinking. Cell wall components are altered, specifically the pectin layer, which increases the union between cells forming a conglomerate. We observed a greater laxity of the cell wall and an increase in the amount of pectin, fact that agree with the phenotype of transgenic plants that overexpressed starch binding domains of Arabidopsis thaliana starch synthase III. Apart from lack of an efficient harvesting technology, one of the major difficulties in using algae is their recalcitrant cell wall, which, on the other hand, is considered as an excellent food supplement. The presence of sugars in the cell wall following hydrolysis facilitates bioethanol production. Our results suggest that transgenic Scenedesmus have an advantage for the production of biofuels in terms of better access to the inner cellulose layer and facilitate its degradation and saccharification.