The Influence of Microbial Siderophore Production on the Transport of Bioavailable Iron in an Alaskan Estuary

Abstract:

Marine life and associated ecosystems are significantly affected by iron since all living organisms require iron for various metabolic processes. Organisms in oxic environments such as the ocean can be iron limited. A deficiency in iron can affect primary producers and produce a negative cascade down the food chain. It is, therefore, critical to understand how bioavailable iron is transported. Estuaries act as bridges by connecting nutrients and elements from saltwater and freshwater ecosystems. However, higher salinities cause increased iron flocculation and loss of bioavailable iron. Iron can be maintained in solution through the complexation with siderophores and most iron found in oceans is bound to organic ligands. It is hypothesized that microbial siderophore production in estuaries are critical for maintaining bioavailable iron. To identify microbial siderophore production in an Alaskan estuary and discover if bioavailable iron is affected by microbial siderophore production, samples through the salt gradient of the Kenai River in Alaska were collected. Samples were analyzed for major ions and trace metals to determine environmental characteristics of the estuary. DNA was extracted from water and sediment samples for metagenomic sequencing and the 16S rRNA gene was PCR amplified for sequencing on an Illumina MiSeq. 16S rRNA gene and metagenomic sequencing detected putative organisms that can produce siderophores in all samples and, microbial diversity of these putative siderophore producing microbes increased with salinity. Chemical analysis showed an increase in total magnesium, potassium, sulfate, and calcium based on sodium concentrations while total iron concentrations showed variation. Metagenomic DNA revealed a lack of siderophore biosynthesis genes in samples with low sodium concentrations. Microbes are likely involved in maintaining bioavailable iron as salinity increases through an estuary. Further work will identify and quantify siderophore genes.