If you have an ACS member number, please enter it here so we can link this account to your membership. (optional)

ACS values your privacy. By submitting your information, you are gaining access to C&EN and subscribing to our weekly newsletter. We use the information you provide to make your reading experience better, and we will never sell your data to third party members.



Helium ion microscopy reveals mysteries of spiky bacterial filaments

Iron-oxidizing bacteria make organic scaffold that accumulates iron minerals

by Deirdre Lockwood, special to C&EN
April 29, 2018 | A version of this story appeared in Volume 96, Issue 18


Micrograph made using helium ion microscopy shows iron oxide hyroxide mineral deposits coating a spiral filament.
Credit: James M. Byrne
Iron-oxidizing bacteria form twisted stalks that accumulate iron oxide-hydroxide crystals.

Some iron-oxidizing bacteria make organic-mineral filaments that extend from their surfaces. But how they are formed remains a puzzle. Now, using helium ion microscopy (HIM), James M. Byrne of the University of Tübingen and his colleagues have captured these stalks forming in unprecedented detail (Environ. Sci. Technol. Lett. 2018, DOI: 10.1021/acs.estlett.8b00077). Previous imaging efforts used scanning electron microscopy, but this technique has inferior resolution and in this context requires coatings that distort the structures being studied. The group cultured bacteria isolated from low-oxygen sediments in a Denmark bay and analyzed the samples with HIM over a month to document how the structures changed. First, spiral-shaped stalks formed. Eventually, mineral crystals coated the spirals so heavily that their shapes were no longer discernible. “It really blew my mind when we started to see these objects forming,” Byrne says. The spirals were mostly organic, whereas the mineral deposits were lepidocrocite, an iron oxide-hydroxide mineral, elemental analysis showed. Some researchers think the structures sequester toxic, dissolved iron(II) in the environment as insoluble iron(III), protecting the microbes. More work may solve that mystery, too.


This article has been sent to the following recipient:

Chemistry matters. Join us to get the news you need.