Phytoplankton Friday: Part 2

Happy Independence Day to my fellow Americans! Today I am off for the holiday but I am sitting in my nice, quiet office to write this blog post. Holidays are often wonderful times to get work done because the office and lab are quiet. But it is also important to enjoy life, and so later this afternoon I am heading out of town to do just that!

This week I mostly spent my time getting caught up in the lab--remembering where I'm at with experiments, doing general maintenance, and catching up with email and paperwork. As with any job, as a scientist I end up doing some work that is not strictly research but has to be done anyway (administrative paperwork, etc.). Next week I will be ready to get back to doing experiments, although we have some training for the ICP-MS that I have to attend, and I'll report next week on that.

As promised, today is Phytoplankton Friday Part 2. In my very first blog post, I alluded to the fact that organisms require trace metals as micronutrients, including phytoplankton and people. Trace metals are needed as cofactors in metalloenzymes. Let's break that down: Enzymes are proteins that catalyze, or greatly speed up, biochemical reactions. Metalloenzymes, as the name implies, have a metal (the cofactor--sort of a helper) at the active site. One example of a metalloenzyme that most people are familiar with is hemoglobin. Hemoglobin is used to transport oxygen in the blood and contains iron (Fe) at the center of a porphyrin (the ring containing the nitrogen (N) atoms). Phytoplankton also require Fe, although obviously for some different enzymes, such as those associated with performing photosynthesis. In addition to Fe, phytoplankton require zinc (Zn), copper (Cu), cobalt (Co), manganese (Mn), and molybdenum (Mo), plus a few other metals. Often, the job of a metal in an enzyme is to move electrons.

Phytoplankton must acquire trace metals from their surrounding environment. In some oceanic regions, such as the Southern Ocean, Fe limits phytoplankton primary production. Because trace metals are precious resources, some phytoplankton have the ability to store Fe and other nutrients for later use (luxury storage), and phytoplankton can also change their metal uptake rates depending on ambient metal concentrations. Interestingly, coastal diatoms--where nutrients are abundant--have higher micronutrient requirements than diatoms that live in the open ocean--where nutrients are much scarcer. Phytoplankton are truly well adapted to their environments.

On a side note, some bacteria play a very important role by transforming atmospheric nitrogen (N₂) into biologically useful forms of nitrogen, starting with ammonium (NH₄⁺). This is a rather difficult reaction, and it is catalyzed by an enzyme called nitrogenase. Notice that this enzyme requires molybdenum. So here is yet another reason to study molybdenum and how it is related to the evolution of life on earth.