Impact of Silicate Limitation on Diatom Mortality in the Equatorial Pacific Ocean

Abstract

I explored how Thalassiosira oceanica cells responded when an infectious agent from the Equatorial Pacific Ocean entered its cells under silicate limited conditions. T. oceanica is an open ocean phytoplankton, specifically a diatom, which creates its cell walls out of silicate. T. oceanica is a model organism because of its small yet fully sequenced genome and fast growth rate. Research in host-virus dynamics in diatoms is new, especially in open ocean environments. Viruses play a significant role in the biogeochemical cycle, the movement of nutrients and elements through biotic and abiotic factors, by adding organic matter of diatoms to the microbial loop. They do so through a reproductive process called the lytic cycle when enough viruses replicate within a cell and cause it to burst or lyse. In the Equatorial Pacific Ocean, it is known that iron is the limiting factor inhibiting phytoplankton growth. However, it is hypothesized that silicate is the limiting factor instead of iron in this region. A recent study has found that silicate limited regions increase diatom virus infection due to thin cell walls, allowing for viruses to enter easily. However, research on marine viruses in open ocean environments like the Equatorial Pacific Ocean has yet to be conducted. I hypothesize that a silicate limited environment will increase diatom virus infection in the Equatorial Pacific Ocean. The results from growing infected T. oceanica in well plates display that 29.7% of dying and uncertain wells in silicate limited conditions died more than in replete conditions, representing only 1.6%. Higher mortality rates of T. oceanica can impact the silicate cycle and carbon export rates in the surface oceans to decrease over time while increasing the viral shunt.