Changes in bacterial community composition along a solar radiation gradient in humic waters

It has been demonstrated that solar and particularly UV-radiation has strong effects on the production, activity and abundance of bacterioplankton, whereas effects on bacterial community composition (BCC) are unclear. We performed 3 independent experiments where humic water (either from a lake or a swamp) was incubated at different depths to create a gradient of intensity of exposure to natural solar radiation. Bacterial community composition, as assessed by terminal restriction fragment length polymorphism analysis (t-RFLP), changed gradually with increasing depth in parallel to decreasing sunlight exposure. Vertical changes in the production of dissolved inorganic carbon, oxygen consumption and bacterial production coincided with changes in BCC, suggesting a relationship between bacterial community composition and function.