www.aquaticmicrobial.net

Abstract

Despite recent advances and new applications of molecular and biogeochemical methodology in aquatic microbial ecology, our perception of the aquatic microbial world remains one dominated by “free-living” bacteria that account for most of the microbial activities in the pelagic zone. Recent research has, however, shown that there exist vast and hidden “microbial networks” within the water column, connected via various microhabitats such as aggregates, fecal pellets and higher organisms. Bacterial abundance within these networks may rival or exceed that of the “free-living” bacteria. Hence, what we have learned in traditional aquatic microbial ecology represents merely a fraction of the microbial world. Within these networks a bacterium can travel long distances, communicate and closely interact with other bacteria, and efficiently exchange genetic information with one another. The presence of microbial networks within the water column demands better sampling strategies and a new way to understand bacterial ecology, evolution and functions within the broader context of systems biology.

Acknowledgements

H.P.G. received funding from the German Science Foundation (DFG-GR 1540/11-1, 12-1 and PA 1655/1-1) and the Leibniz Foundation. K.W.T. was supported by U.S. National Science Foundation grant OCE-0814558 and a visiting scientist fellowship from Leibniz Institute of Freshwater Ecology and Inland Fisheries, Berlin.

Figures and Tables

Figure 1 Different conceptual views of the aquatic microbial ecosystem. In the traditional view (A), bacterial communities are mainly dominated by free-living bacteria and attached bacterial communities in microniches are rather isolated from each other. Water column stratification also limits exchanges of bacteria between water layers. In our proposed microbial networks (B), free-living and attached bacteria are tightly linked with each other via a network of microhabitats represented here by aggregates, fecal pellets, plankton and higher organisms. Mobile organisms also effectively transport bacteria over long distances and across boundaries. Within a microhabitat, such as a copepod, dense populations of diverse bacteria can closely communicate and exchange genetic information with each other, be protected from external hazards, exploit high concentration of organic matters and drive biogeochemical reactions that are otherwise not favored in the surrounding water.