Osmoregulation in the euryhaline flagellate Brachiomonas submarina (Chlorophyceae)

Brachiomonas submarina Bohlin (Chlorophyceae), a euryhaline marine flagellate, can osmoregulate over a wide range of external salinity. The alga exhibits maximum water content at 100% artificial seawater (ASW), and shows only a small water loss (<15%) when salinity is increased to 300% ASW. The non-aqueous volume of the cells is increased at salinities higher than 100% ASW. This is partially attributable to the accumulation of glycerol. Glycerol is the major osmoregulatory organic solute in this flagellate. The alga also shows an accumulation of amino acids in response to increased salinity. The contribution of glycerol and amino acids to intracellular osmolarity is only 9% at 10% ASW, but accounts for 49% at 300% ASW. The remainder of the osmotic balance is due to uptake and accumulation of inorganic ions, particularly sodium, potassium and chloride.