Salicylic acid and aspirin stimulate growth of Chlamydomonas and inhibit lipoxygenase and chloroplast desaturase pathways.

Chemical stimulants, used to enhance biomass yield, are highly desirable for the commercialisation of algal products for a wide range of applications in the food, pharma and biofuels sectors. In the present study, phenolic compounds, varying in substituents and positional isomers on the arene ring have been evaluated to determine structure-activity relationship and growth. The phenols, catechol, 4-methylcatechol and 2, 4-dimethyl phenol were generally inhibitory to growth as were the compounds containing an aldehyde function. By contrast, the phenolic acids, salicylic acid, aspirin and 4-hydroxybenzoate markedly stimulated cell proliferation enhancing cell numbers by 20-45% at mid-log phase. The order of growth stimulation was ortho > para > meta with respect to the position of the OH group. Both SA and aspirin reduced 16:3 in chloroplast galactolipids. In addition, both compounds inhibited lipoxygenase activity and lowered the levels of lipid hydroperoxides and malondialdehydes in the cells. The present study has demonstrated the possibility of using SA or aspirin to promote algal growth through the manipulation of lipid metabolising enzymes.