As a microbiologist, I’m used to studying things I cannot see. Microorganisms inhabit the world around us, living in places too harsh for humans (like hot springs, salt lakes, and in sea ice). They are also incredibly abundant with estimates of 1030 cells on the planet (there are an estimated 1021 stars in the universe, for comparison), yet we cannot see them without help from an instrument like a microscope. It is amazing to think that every surface we can touch or walk upon or swim in is filled with microorganisms, many of which are responsible for cycling important compounds to keep life on earth going.
When we use the term “microorganism”, we can be referring to Bacteria (the most common), Archaea, or small Eukaryotic (like plants or animals) cells. I study Archaea, which are similar to Bacteria in that they are organisms with only a single cell (whereas the human body is made up of 1013 cells). However similar they appear on the outside, they are quite different on the inside, and some of their cellular functions match what is found in Eukaryotes like us. This makes them an interesting group for study, especially in the ocean where it is estimated that 20-30% of all single cells come from one group of Archaea, called the Thaumarchaeota.
Thaumarchaeota (or “Wonder Archaea”) get energy from converting ammonia to nitrite, much like we eat food to do things like run. I started working with this group during graduate school, and have been amazed at how little we know about them despite how many exist on Earth. In particular, I am curious as to how changes in environmental conditions can impact their metabolism to help predict what may happen to these communities as the Earth changes over time.
For this cruise, I have been filtering seawater through small filters that trap the cells so I can extract their DNA and RNA. Although this method does not select specifically for Thaumarchaeota, I will be able to view them in the context of all microorganisms in community. I have been using the CTD sampling rosette to capture seawater from multiple depths in the ocean. From each water sample, I will sequence the 16S rDNA to determine which microorganisms are present in the sample and use 16S rRNA as a proxy for which are active. In addition, I am using stable isotope tracers of ammonia (15NH4Cl) and bicarbonate (H13CO3) to directly measure how quickly the community is oxidizing ammonia for energy or fixing carbon to build biomass. I also have an experiment planned with Bryn that we will talk about later, involving differences in microbial growth under light or dark conditions.
Posted by Bradley