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Outer Membrane Iron Uptake Pathways in the Model Cyanobacterium Synechocystis sp. Strain PCC 6803
- Source :
- Applied and Environmental Microbiology. 84
- Publication Year :
- 2018
- Publisher :
- American Society for Microbiology, 2018.
-
Abstract
- Cyanobacteria are foundational drivers of global nutrient cycling, with high intracellular iron (Fe) requirements. Fe is found at extremely low concentrations in aquatic systems, however, and the ways in which cyanobacteria take up Fe are largely unknown, especially the initial step in Fe transport across the outer membrane. Here, we identified one TonB protein and four TonB-dependent transporters (TBDTs) of the energy-requiring Fe acquisition system and six porins of the passive diffusion Fe uptake system in the model cyanobacterium Synechocystis sp. strain PCC 6803. The results experimentally demonstrated that TBDTs not only participated in organic ferri-siderophore uptake but also in inorganic free Fe (Fe′) acquisition. (55)Fe uptake rate measurements showed that a TBDT quadruple mutant acquired Fe at a lower rate than the wild type and lost nearly all ability to take up ferri-siderophores, indicating that TBDTs are critical for siderophore uptake. However, the mutant retained the ability to take up Fe′ at 42% of the wild-type Fe′ uptake rate, suggesting additional pathways of Fe′ acquisition besides TBDTs, likely by porins. Mutations in four of the six porin-encoding genes produced a low-Fe-sensitive phenotype, while a mutation in all six genes was lethal to cell survival. These diverse outer membrane Fe uptake pathways reflect cyanobacterial evolution and adaptation under a range of Fe regimes across aquatic systems. IMPORTANCE Cyanobacteria are globally important primary producers and contribute about 25% of global CO(2) fixation. Low Fe bioavailability in surface waters is thought to limit the primary productivity in as much as 40% of the global ocean. The Fe acquisition strategies that cyanobacteria have evolved to overcome Fe deficiency remain poorly characterized. We experimentally characterized the key players and the cooperative work mode of two Fe uptake pathways, including an active uptake pathway and a passive diffusion pathway in the model cyanobacterium Synechocystis sp. PCC 6803. Our finding proved that cyanobacteria use ferri-siderophore transporters to take up Fe′, and they shed light on the adaptive mechanisms of cyanobacteria to cope with widespread Fe deficiency across aquatic environments.
- Subjects :
- 0301 basic medicine
Cyanobacteria
Siderophore
Iron
030106 microbiology
Mutant
Siderophores
Applied Microbiology and Biotechnology
03 medical and health sciences
Bacterial Proteins
Environmental Microbiology
Ecology
biology
Strain (chemistry)
Chemistry
Carbon fixation
Synechocystis
Wild type
Membrane Transport Proteins
Biological Transport
biology.organism_classification
030104 developmental biology
Mutation
Biophysics
bacteria
Bacterial outer membrane
Food Science
Biotechnology
Subjects
Details
- ISSN :
- 10985336 and 00992240
- Volume :
- 84
- Database :
- OpenAIRE
- Journal :
- Applied and Environmental Microbiology
- Accession number :
- edsair.doi.dedup.....0b00ce01745f5b68c9cf99016f1d3960