Single cell activity of aerobic anoxygenic phototrophic bacteria in the Delaware Estuary

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University of Delaware
Aerobic anoxygenic phototrophic (AAP) bacteria are abundant in estuaries, coastal regions and in the open ocean, comprising 1-30% of total prokaryotes. To understand their distribution and potential contribution to the carbon cycle, single cell activity of the microbial community was determined by 3H-leucine incorporation detected using microautoradiography combined with additional steps to identify AAP bacterial cells before and after microautoradiography. The approach was used on transects through the Delaware estuary in August and November 2011. The percent of active AAP bacteria was up to two fold higher than the percentage of active bacteria for the rest of the bacterial community in the estuary. Likewise, the silver grain area associated with active AAP bacteria was larger than that for the rest of the community, indicating higher rates of leucine consumption by AAP bacteria. The difference between the activity of AAP bacteria and other bacteria was greatest in high salinity waters and was lowest in freshwater. The incorporation of 3H-leucine by AAP bacteria did not vary with light under ambient light conditions as well as in incubations with constant light and darkness. Our results suggest that AAP bacteria are more active than other bacteria in many parts of the estuary, just not in all locations.