Findings: Iron Interactions

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Iron is essential for bacterial survival–it is the most common redox active metal found in proteins. These proteins are needed for essential processes such as respiration, central metabolism, and DNA repair (Frawley 2015). This week, we investigated how iron affects Delftia acidovorans. There’s evidence that iron could affect gold biomineralization, antimicrobial activities, and plant growth, but we wanted to learn more. Here’s what we found.

Iron Reduces Gold Biomineralization

One study we annotated this week found that Delftia was able to grow best in gold solution without iron. When exposed, delftibactin could still function sufficiently enough to detoxify gold ions and support the growth of colonies (annotation)(Johnston et al. 2013). This suggests that iron somehow competes with gold for delftibactin, which reduces gold-binding activity. More research is needed to determine how these interactions occur. 

The same paper also found that the amount of delftibactin changed when iron was added. This is strong support for siderophore (iron interacting) activity in delftibactin. Delftibactin concentration decreased as the concentration of iron increased, but the specific relationship between these two biomolecules is yet unknown.


A graph showing that an increased concentration of iron causes a decrease in the concentration of delftibactin.
There is an inverse relationship between the concentration of iron and delftibactin. When iron exceeds 1.0E-04M, the growth of Delftia was hindered. Data adapted from Johnston et al. 2013 (Supp. Table 6).


Another paper found that delftibactin retains its solubility when bound to iron (Wyatt et al. 2014). An annotator proposed that this could allow delftibactin to return iron to Delftia (annotation). It would be interesting to see if Delftia’s iron-acquisition abilities are reduced in the delG strain created by Johnston et al. (2013). This strain does not produce delftibactin, and this mutation could also affect iron uptake. This could allow us to further characterize delftibactin’s role as a siderophore.

To develop gold-precipitating applications such as recycling gold in e-waste, we must fully understand the interactions between delftibactin and iron. Preliminary evidence shows that iron reduces the efficiency of gold precipitation. Perhaps iron could be removed first from e-waste, so that scavenging Delftia is not affected by it. Alternatively, it may be possible to create a peptide similar to delftibactin that isn’t susceptible to iron interactions.


Delftibactin binds pathogens more rapidly than iron

A study that looked into the antimicrobial properties of delftibactin against Methicillin-resistant Staphylococcus aureus (MRSA). When purified delftibactin was added to colonies of MRSA, growth was significantly inhibited which indicates that delftibactin may be an antibiotic compound. Researchers also found that the addition of iron did not affect the antimicrobial effects of delftibactin. Interestingly though, when delftibactin was incubated with iron (at 1:1 and 1:10 ratios), the antibiotic effects were significantly diminished (Tejman-Yarden et al. 2019). One explanation for this could be that delftibactin typically binds to a pathogen quickly, but if delftibactin is incubated in iron first the active site becomes bound and unable to target pathogens.  


Delftia has unique genes for iron uptake and use

Some Delftia strains such as RAY209, associate with plant roots and possibly promote growth. Plants deposit rich nutrients into the soil which support many types of bacteria. These root-associated bacteria are collectively called rhizobacteria. Sequencing found that the D. acidovorans strain RAY209 has unique genes related to iron acquisition and metabolism (Perry et al. 2017). These genes could be especially essential to the growth of Delftia, as one annotator pointed out (annotation). Rhizobacteria are known to interact with iron to potentially promote plant growth. RAY209 is believed to benefit canola and soybean crops, but we don’t know how this occurs. 


Annotation from R_krebs highlighting the importance of iron uptake for bacterial survival.
This annotation pointed out how important it is that bacteria have adequate iron. Annotation on Tejman-Yarden et al. 2019).


What do you think about Delftia’s interactions with iron? Did we miss anything? Annotate this page and let us know!

Check out this week’s topic, and help us learn about Delftia’s ideal environment for gold biomineralization.