Flow Cytometer

Marine Microbes

Marine ecosystems are composed of diverse communities of interacting organisms. The most numerous creatures in the world’s oceans are not fish or whales but microbes that are smaller than the width of a human hair. These microscopic organisms drive biogeochemical cycles and play critical roles in controlling the climate.  For example, about half of the sunlight-driven photosynthesis that occurs on our planet is due to the microscopic algae that live in the ocean.  The microbes that live deep in the ocean away from the sunlight process both inorganic and organic matter, helping to make this material more available as food for larger organisms.


Microbes and Responses to Environmental Changes

The growth of marine microbes is directly linked to environmental conditions, so identifying which and how many microbes are present is the most basic “read-out” of any given ecosystem.  By studying the microbial communities of our oceans, we can begin to understand how marine ecosystems will respond to both short-term and long-term changes in the environment.


The Flow Cytometer

Flow cytometers are instruments originally developed for biomedicine that can analyze the size and fluorescent characteristics of individual cells within a complex mixture.  Our flow cytometer has been specially modified by collaborators at Cytopeia to examine the microscopic organisms that live in the seas. 


Pigments and Fluorescence

Like land plants, microscopic algae (phytoplankton) in the ocean contain pigments such as chlorophyll a that allow them to capture and use the energy from sunlight.  Different species of phytoplankton use pigments that capture slightly different wavelengths of light. The fluorescent characteristic of different groups of phytoplankton depends on their individual combination of pigments. The naturally occurring fluorescence resulting from pigments can be detected with the flow cytometer, and in combination with cell size, can be used to identify different phytoplankton.  Not all microbes contain pigments, however.  In fact, most microbes in the oceans do not fluoresce at all. We detect these organisms by staining them with compounds that fluoresce when bound to DNA, for example.


Identifying Individual Cells and Organisms

The flow cytometer can thus be used to rapidly determine both the size and fluorescence patterns of individual cells, regardless of whether or not they contain naturally occurring pigments. We also use the size and fluorescent characteristics to identify organisms of interest that we can sort out of the sample stream and into test tubes for additional analyses.  We can also sort cells into growth media so we can grow and study the cells in more detail in the laboratory.


Leo Goes to Sea

The flow cytometer on the VISIONS ’05 cruise is named Leo and normally lives in Dr. Virginia Armbrust’s nice air-conditioned laboratory on the University of Washington in Seattle. To take this instrument out to sea meant that we had to bolt it to the deck of the ship, strap all the parts (such as the computer and various small parts) to the instrument, and then encase it within its packing crate so nothing would be broken if someone stumbled into it in rough seas.  This is the maiden voyage of Leo, and we can’t wait to see how he performs on the high seas.