IRON AS A DRIVING FORCE OF LIFE: INVESTIGATING EFFECTS OF IRON SOURCE ON PHYSIOLOGICAL FACTORS AND BIOTIC IRON RELATIONSHIPS IN SYNECHOCOCCUS SP. PCC 7002

Abstract

Iron is one of the most abundant elements in the Earth’s crust, and yet it is a limiting factor for primary production in large parts of the world’s oceans. This is due to the low solubility of iron throughout the water column and the low bioavailability of many iron forms found in ocean waters and is further affected by local environmental sources such as temperature, pH and redox conditions.

Cyanobacteria are unique prokaryotes, in that they are able to carry out oxygenic photosynthesis. These photosynthesizing bacteria successfully inhabit a wide range of environmental conditions, including marine waters. The photosynthetic machinery of cyanobacteria requires a large number of iron atoms to function satisfactorily, and the organism thus depends of efficient iron uptake strategies in order to meet these demands.

This study was set up as a collaboration between the Department of Chemistry and the Department of Biotechnology and Food Science, and an aim of this collaboration was to design and perform interdisciplinary research.

In this study, we investigated the effect of iron source on iron acquisition in the cyanobacterium Synechococcus sp. PCC 7002 (hereafter Synechococcus). This was done by supplying bulk cultures of wild type organisms as well as targeted deletion mutants with different iron sources and evaluating effects on growth and changes to the photosynthetic machinery, as well as on the biotic reduction of and internalization of iron. Our results show that there is a distinct difference in Fe (II) measured in cultures of Synechococcus and Fe (II) measured in abiotic controls, suggesting a biotically mediated iron reduction process. We also show that iron source affects extracellular iron association as well as internalization of iron, and that iron limiting conditions produce more stress when iron is supplied as a crystalline iron form compared to an easily soluble iron-salt. Results indicate that the presence of siderophores is important for iron acquisition at low iron concentrations, and that the importance is increased when supplied iron concentration decrease. We also show that the internalization of iron is greatly affected both by available iron source and iron acquisition mechanisms.