Using a Bioluminescent Bacterial Bioreporter to Assess Iron Bioavailability in the Oceans

Recent improvements in modern analytical methods have considerably increased our understanding of Fe biogeochemistry in the Ocean. Compiled data have shown that Fe concentrations are low in most open ocean surface waters and that the bioavailability of this Fe is influenced by organic complexation. Of presumed biotic origin, the importance of this organic complexation to Fe availability remains to be elucidated. Unfortunately, current analytical tools do not allow for a linkage to be established between Fe speciation to Fe bioavailability.

To supplement chemical analyses, we have developed a bioanalytical tool: a heterotrophic bacterial bioluminescent reporter system that responds quantitatively to bioavailable Fe concentrations. Data collected during one field study in a freshwater system as well as three independent field studies in marine systems demonstrate that these whole-cell biosensors are a powerful tool for environmental monitoring, providing both qualitative and quantitative insights on Fe biogeochemistry.

To complement this work, laboratory studies have been carried out to characterize the influence of various sources of Fe-complexing organic ligands, including synthetic chelators, bacterial and fungal siderophores and virus-mediated bacterial lysis products. The results of this study will be presented in the context of attempting to clarify the role that the organic complexation of Fe may play in regulating Fe bioavailability to the diverse planktonic components of the aquatic microbial community.

To improve our abilities to standardize this tool in the field, a green fluorescent protein gene expressed under control of a constitutive promoter has been introduced in the genomic DNA of P. putida FeLux. The resulting dual bioreporter will allow for the enumeration of bioreporter cells in environmental samples in parallel to the detection the bioluminescent signal in response to changes in Fe bioavailability.