Helena van Tol

Helena van Tol

Graduate student

Benjamin Hall IRB 323


  • M.Sc. Oceanography. University of Washington, Seattle, WA, 2015.
  • B.Sc. Environmental Science (Hon.), Biology minor. Mount Allison University, Sackville, NB, 2011.



Effect of Croceibacter atlanticus on cell division in Thalassiosira pseudonana:

For my Master’s project I studied interactions between the flavobacterium Croceibacter atlanticus and diatoms. C. atlanticus was isolated from the pennate chain-forming diatom Pseudo-nitzschia multiseries, and was found to inhibit growth in many different diatoms. When C. atlanticus was grown with the centric diatom Thalassiosira pseudonana, we observed large polyploid cells with multiple plastids. These features indicate that C. atlanticus may inhibit cytokinesis in diatoms.

T.pseudonana polyploidy
Epifluorescence microscopy image of T. pseudonana in mono-culture (left) and in co-culture (right) with C. atlanticus. Green = SYBR-stained DNA, red = plastid autofluorescence.

Constraint-based metabolic modeling of interaction between Thalassiosira pseudonana and Ruegeria pomeroyi:

I am creating genome-scale metabolic models of the diatom Thalassiosira pseudonana CCMP 1335 and the bacterium Ruegeria pomeroyi DSS-3 to investigate the dynamics of interaction between these two model marine organisms under different nutrient conditions. Constraint-based metabolic models can be used to study the flux of metabolites and nutrients in marine microbes, connecting molecular information to the environment. These models have been used to integrate a wealth of different information types and to predict the metabolic behaviour of many different organisms. In culture, growth of the diatom Thalassiosira pseudonana can be supported by vitamin B12-producing bacteria such as Ruegeria pomeroyi. In exchange R. pomeroyi receives organic carbon and sulfur from T. pseudonana. Vitamin B12 is the only organic compound required by most diatoms and it has been demonstrated that R. pomeroyi consumes 2,3-dihydroxypropane sulfonate (DHPS) and N-acetyltaurine produced by T. pseudonana, although there may be other molecules exchanged between these two organisms. I will used these models to study the dynamics of this interaction under different nutrient conditions and investigate the possible exchange of other molecules.