MBL microbial diversity course

In the summer of 2010, I spent six inspiring, challenging, and chaotic weeks at the Marine Biological Laboratory Microbial Diversity Course in Woods Hole, MA. I hoped to take full advantage of the opportunity granted by course directors Steve Zinder and Dan Buckley of Cornell to plunge head on into the world of microbiology. I was eager to learn the theory and hands-on methods to study the microbial world, which has such a profound impact on atmospheric composition, and this course gave me a chance to explore my interests in a way not offered anywhere else.

We were busy for all our waking hours. At first our schedule was filled with lectures and lab exercises. We learned many methods, from the isolation and enrichment of particular microorganisms from the environment to metagenomic analysis of entire environmental microbial communities. The last few weeks were focused entirely on our own ‘mini-projects’. We were encouraged to select projects based on our curiosity, and not necessarily on pertinence to our work back at home. This approach allowed us to explore and experiment without any pressure. We were learning and researching for the pure pleasure of satisfying our curiosity, and we worked all the harder for it.

I became interested in the symbiosis between the cyanobacteria Anabaena sp. and a small epibiont organism attached to the outside of particular cyanobacteria. In lectures, we learned that chains of Anabaena cells accomplish both oxygen-evolving photosynthesis and oxygen-sensitive nitrogen fixation by mandating each cell in the chain to perform one task or the other. In this fashion, fixed carbon from photosythesis and fixed nitrogen can be shared between the cells with different function, and the carbon and nitrogen needs for all are satisfied. The nitrogen-fixing cells are called heterocysts and are greatly outnumbered by the carbon fixing vegetative cells. Interestingly, the epibiont bacteria only attaches to the nitrogen-fixing heterocysts of Anabaena.

I wondered whether the H₂ produced by nitrogen-fixation in the heterocysts, which is a phenomenon that necessarily occurs given the nitrogenase enzymes involved, is utilized by the epibionts; could H₂ be what draws the epibionts to attach to the heterocysts? Hydrogen is a molecule packed with energy for organisms with a hydrogenase enzyme to utilize it, and this ability is not uncommon. Therefore, I set out to study Anabaena and its epibiont to see if hydrogen exchange could be a component, or the key reason, for their symbiosis.

Here is my paper on this project Meredith Microbial Diversity Report 2010