Research Project: VSP Staining of Bacteria
VSP Stained bacteria taken from SkIO dock.
Bacteria are thought to be second only to phytoplankton in the role of living organisms in the transformation of organic carbon in aquatic ecosystems. In open ocean waters, the biomass of bacteria has been reported to exceed that of all other living plankton, and even in continental shelf and coastal waters it is significant compared to other plankton. However, these estimates are all derived from the assumption that all DAPI-stained cells are metabolically active cells. This hypothesis no longer appears tenable: a large fraction of apparent bacteria are either inactive, moribund, or dead. Such a conclusion threatens to precipitate another paradigm shift in conceptual models of ecosystem function. At the very least, it would imply that a comparatively few bacteria in situ are growing (and respiring) much faster than previously thought, and that a large fraction of "apparent" bacteria are really a component of detritus.
In conjunction with Dr. M. E. Frischer, we have developed a novel combination of a fluorescent stain and molecular probes which quantitatively identify those cells with compromised membranes, and those cells containing sufficient rRNA to be considered metabolically active. While neither one might be considered sufficient to specify active from inactive, moribund, or dead cells, together they comprise a powerful tool to investigate the relative importance of these cell types in situ, and to postulate which sources of bacterial mortality may be important at a given time and place. We are currently evaluating viability and sources of bacterial mortality, and will eventually use these methods to document temporal patterns in field communities of bacteria, and investigate causative agents of those patterns.