Functional and structural imaging of phototrophic microbial communities and symbioses

In recent years, new imaging methods for mapping microhabitats, solute concentrations, microbial activity and photopigment content have been developed and increasingly applied in different areas of aquatic microbial ecology and biogeochemistry. Such techniques exhibit a spatial resolution similar to that of microsensors, but allow for instantaneous mapping of the 2-dimensional distribution and dynamics of solute and pigment concentrations over areas ranging from mu m(2) to several cm(2). Methods have been developed for imaging O-2 and CO2 concentrations as well as pH with optical sensor foils (i.e. planar optodes), and for combined imaging of photopigments and photosynthetic activity via variable chlorophyll fluorescence. More recently, hyperspectral imaging has been employed to identify pigment content in individual cells and to visualize the spatial organization of functional groups in photosynthetic microbial communities. We give an overview of these emerging methods with a range of illustrative examples to demonstrate how they can provide useful information in functional and structural studies of a variety of aquatic microbial communities, such as sediments, biofilms, coral tissues or photosynthetic mats.