To B12 or not to B12, that is the question…

Bryce Penta, University of Notre Dame

As the summer draws to an end, so too does this segment of my research with phytoplankton and vitamin B12. After completing three separate experiments, my project has finally reached its end.

One experimental design encompassed the first two experiments and used a mixed community of phytoplankton straight from the ocean while aboard the R/V Savannah, while the other relied on a culture of Phaeodactylum tricornutum, a phytoplankton species, that had all bacteria removed in laboratory settings. The first pair of experiments were conducted with an addition of both vitamin B12 and nitrate and the final experiment implemented a limitation of the same two nutrients. I specifically looked at the effect of varying availability of these nutrients on the photosynthetic efficiency and growth of the cultures.

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Photo confirming the lack of bacteria in the phytoplankton cultures in lab. The picture also shows that the cultures contained two body forms of Phaeodactylum tricornutum. Photo credit: Lena Pound

This study proposed that an increase in the availability of these nutrients would lead to an increase in efficiency and growth, as well as a decrease leading to a lower efficiency and growth. While we expected an effect of vitamin B12 on the phytoplankton functioning, in all three experiments B12 lacked any significant effect; however, nitrate showed a strong effect on the photosynthetic efficiency and growth in all experiments except the deep sea boat experiment.

While only nitrate exhibited a significant effect on the phytoplankton, this could be due to an alternate metabolic pathway that can bypass the need for vitamin B12. Using methionine synthase E (MetE) rather than the more efficient methionine synthase H (MetH) that requires vitamin B12, the Phaeodactylum tricornutum cultures functioned properly in the absence of vitamin B12 (Helliwell et al. 2011). Unlike the laboratory experiment, the ocean experiments may have lacked a B12 response due to microbes in the water already producing more than enough of the nutrient. Vitamin B12 lacked significant response in our experiments, but other experiments with species that lack the MetE synthase that allows for proper functioning without vitamin B12. Possible B12 effects on phytoplankton could lead to better climate modeling as phytoplankton form the basis of one of the world’s largest ecosystems.

These past ten weeks have culminated in a project that I am proud to have worked on this summer. Though my time here has ended, the people I have met here and the relationships formed over the summer will continue on in the future.

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Lee lab on the R/V Savannah showing off the catch of the trip, a 55 inch wahoo. Photo credit: Bryce Penta

Acknowledgements

This project is possible due to funding from the NSF College of Charleston Summer REU program and the Grice Marine Laboratory. Project ideation and collaboration with Dr. Peter Lee and the Di Tullio lab from the College of Charleston. Lab space and facilities provided by the Hollings Marine Laboratory.

References

Helliwell, K.E., Wheeler, G.L., Leptos, K.C., Goldstein, R.E., Smith, A.G. (2011) Insights into the Evolution of Vitamin B12 Auxotrophy from Sequenced Algal Communities. Molecular Biology and Evolution 28 (10): 2921-2933.

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Even Phytoplankton Need Their Vitamins

Bryce Penta, University of Notre Dame

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Phytoplankton: unlike dolphins and other large marine organisms, these little creatures do not catch the attention of most people. Producing almost 50% of the world’s oxygen, phytoplankton provide a unique research opportunity to learn more about bottom-up controls on the environment. Phytoplankton have long been understood as key factors in ecosystem mechanisms, but the details of their functions still remain poorly understood. After spending the previous summer studying freshwater phytoplankton, I wanted to switch to marine environments to understand more about these small organisms.
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Figure 1. An example of the diversity of phytoplankton, all with various nutrient thresholds, especially in regard to vitamin B12. (Photo credit: Martin 2013)

My project aims to understand the effects of vitamin B12 limitation on the photosynthetic efficiency of the phytoplankton. Photosynthetic efficiency refers to the ability of the organism to funnel as much useable energy as possible into photosynthesis. Certain nutrients and trace elements in limited concentrations affect the ability of phytoplankton to photosynthesize by inhibiting key steps in the metabolic pathway. Vitamin B12, a possible limiting agent, can only be produced by microbes and recently the discovery of these organisms has exploded (New producer discovered, click here to find out more).  I will be altering the nutrient balance for my samples, subjecting them to higher or lower levels of B12 and nitrates. Until recently, most phytoplankton research has focused on inorganic compounds (nitrates, phosphates, etc.), disregarding the importance of biologically active compounds like B vitamins. Under stress of nutrient limitation, the phytoplankton no longer efficiently use the energy from photons and thus emit the energy as fluorescence. The hope of this project is to better understand the influence of vitamin B12 on both mixed phytoplankton samples and a single species culture.

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Figure 2. A fluorometer used to measure the photosynthetic efficiency of phytoplankton by taking the maximum fluorescence and the standard to get a ratio of efficiency.  (Photo credit: ACT Technologies Database)

Ultimately, the goal of this study is to elaborate on previous findings that implicate vitamin B12 in photosynthetic pathways. Few studies utilize B vitamins as a potential factor in phytoplankton systems. From this new understanding of the effect on photosynthetic efficiency, we can advise climate modelers to include or disregard vitamin B12 availability for their models as a potent limiting agent for phytoplankton.

Acknowledgements

This project is possible due to funding from the NSF College of Charleston Summer REU program and the Grice Marine Laboratory. Project ideation and collaboration with Dr. Peter Lee and the Di Tullio lab from the College of Charleston. Lab space and facilities provided by the Hollings Marine Laboratory.

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Resources

Panzeca, C., A.J., Tovar-Sanchez, Agusti, S., Reche, I., Duarte, C.M., Taylor, G.T., Sanudo-Wilhelmy, S.A. (2006) B Vitamins as Regulators of Phytoplankton Dynamics. 596-597.

Sanudo-Wilhelmy, S.A., Gomez-Consarnau, L., Suffridge, C., Webb, E.A. (2014) The Role of B Vitamins in Marine Biogeochemistry. Annual Review of Marine Science. 6: 339-367.

Bertrand, E.M., Allen, A.E. (2012) Influence of vitamin B auxotrophy on nitrogen metabolism in eurkaryotic phytoplankton Frontiers in Microbiology 3: 1-16.

Martin, Claire. (2013) Vanishing Marine Algae Can Be Monitored From a Boat With Your Smartphone. Smithsonian. http://www.smithsonianmag.com/science-nature/vanishing-marine-algae-can-be-monitored-from-a-boat-with-your-smartphone-2785190/?no-ist

“ACT Technologies Database -FLUOROMETER.” ACT Technologies Database -FLUOROMETER. N.p., n.d. Web. 16 June 2015.