Siderophore mediated iron acquisition of psychrophilic Antarctic marine bacteria

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Iron is a highly limited resource in large areas of the Southern Ocean. To compete for the limited and often localized influx of iron, bacteria have developed various biochemical strategies to capture iron and transport it into the cell. The aim of this project is to purify and structurally identify bacterially produced iron ligands, so called siderophores, of a phylogenetic spectrum of cultivable psychrophilic Antarctic marine bacteria obtained from divergent Antarctic environments. A consequential objective is then to correlate iron uptake by different siderophores among these bacteria with environmental parameters (iron stress, carbon availability, salinity and temperature). With this approach, we will unravel the spectrum of iron binding ligands used by Antarctic bacteria and ultimately contribute to a better understanding of microbial adaptations to the extreme environments of the SO.Specifically, 384 bacterial isolates obtained from the Southern Ocean will be cultured under growth regimes reflecting iron depletion. Indicator assays in combination with voltammetry and mass spectrometry will be used to detect siderophores in the bacterial supernatants and cell pellets. This approach will allow us to differentiate siderophore types across cultivable bacterial lineages of Antarctic origin and/or their original habitats. We will structurally elucidate novel siderophores by NMR and MS and purify these and known siderophores for reference standards used for quantitative analyses and experimental determination of physicochemical characteristics. One major aim is to characterize diffusion and adsorption traits for different siderophore types under conditions representative of SO habitats. We will study how environmental parameters (temperature, salinity) influence the iron capturing performance and diffusive losses for each ligand type. These general siderophore characteristics will be used to interpret results from experiments testing bacterial growth and siderophore production dependent on a range of temperature, salinity and ice regimes. This study will ultimately improve existing cellular iron uptake models, increase our knowledge of iron uptake strategies of psychrophilic bacteria and ultimately contribute to a better process understanding of the microbially driven Antarctic iron cycle, therefore addressing several of the central criteria of the DFG SPP call.