While the role of iron as a limiting agent of primary productivity in marine systems has been extensively studied, the response(s) of marine bacteria to changes in iron availability remain less clear. Studies from numerous groups suggest that many marine prokaryotes maintain the ability to produce siderophores (or at least siderophores-like compounds) in response to iron-limiting growth conditions and as such can effectively persist under conditions of low iron availability. While analytical techniques can quantify total iron at incredibly small concentrations and provide information on iron speciation and the kinetics of iron association/dissociation with organic ligands, there are no indicators of the bioavailability of iron in different forms to natural communities. To understand the role that iron plays in global marine productivity, a tool based on the iron-sensing systems of bacteria is needed.
For this reason, a researcher from the University of Tennessee at Knoxville will develop, characterize, and calibrate a series of heterotrophic bacterial bioluminescent bioreporters that quantitatively respond to changes in ambient iron bioavailability. After the construction of a series of new reporter systems, and the tagging of these bioreporters with a constitutive fluorescent protein marker (so that bioreporter cells can be enumerated in the presence of the natural marine microbial population), field tests will be carried out in the subtropical convergence high nutrient-low chlorophyll zone southeast of New Zealand to validate the field use of this reporter and characterize the effects of natural dissolved organic matter of iron bioavailability to different bacteria. Side-by-side comparisons with similar tools being developed in cyanobacteria will provide an understanding of the differences between model heterotrophic and phototrophic iron acquisition strategies. The goal is to develop and validate a tool set that will directly represent a subset of marine bacteria and serve as a comparative in laboratory studies with all cultivable marine bacteria, and in field studies with the variant populations found in diverse locations.
In terms of broader impacts, this study will provide the oceanographic community with a biosensor tool capable of determining iron bioavailability to heterotrophic bacterial communities, a key component towards understanding the biogeochemical cycle of iron in the ocean. It is anticipated that once completed, the bioreporter strains will be available to qualified researchers through the center for Environmental Biotechnology culture collection. Two graduate and two undergraduate student will be trained at this Experimental Program to Stimulate Competitive Research (EPSCoR) institution as part of this project.
