A study contradicting the «Luxury consumption» of silicon by the marine prasinophycean alga, Platymonas

AbstractNatural waters are often low in silicate ion, hence the possible “luxury consumption” of this ion by algae with no known Si-requirement is of major ecological importance to siliceous organisms. A unicellular marine alga, Platymonas sp., was studied in this context under controlled laboratory conditions. Growth rates in pH-regulated cultures were unaffected by silicate concentrations ranging between 1.0 and 230.0 μM Si. No removal of silicate from the medium was observed when the pH of cultures was maintained below 9.0. Without pH control, cultures of Platymonas reached values of pH greater than 9.5, at which time a rapid and essentially complete removal of silicate from the medium was observed. This was not attributable to biological uptake as intracellular silicon was not detected by electron spectroscopic imaging, although a relatively small amount of silicon was observed in association with the cell theca. The sedimented “cell-pellet” harvested from unbuffered cultures at pH > 9.5 contained a f...