Marine alga Platymonas sp. accumulates silicon without apparent requirement

Abstract

THE role of silicon in living systems has only recently begun to be understood. Apart from being an important structural component of diatoms and silicoflagellates¹, some freshwater flagellates², higher plants, sponges and other organisms³, it is necessary for DNA polymerase activity in diatoms⁴ and for bone and tooth development in certain vertebrates⁵. Silicified algal species are known (or assumed) to have an obligate, concentration-dependent silicon requirement for growth^6,2, and transport systems for the accumulation of silicic acid (Si(OH)₄) have been described⁷; however, the uptake of Si(OH)₄ by nonsilicified algae has never been reported. Here we report the accumulation of significant amounts of silicon by the planktonic marine alga Platymonas sp. (isolated during the summer of 1954 from Great Pond, Falmouth, Massachusetts). This alga is very close to, or may be an isolate of P. suecica (personal communication from R. Norris) and has no known silicon requirement, growing equally well in Si-rich and Si-poor environments. Because Si(OH)₄ is a potentially limiting nutrient for diatoms⁸, the removal of available Si(OH)₄ from the environment by organisms that do not require it could play an important role in phytoplankton competition and succession. This phenomenon could also be important in the cycling of silicon in the ocean.