Deep-branching magnetotactic bacteria form intracellular carbonates enriched in trace metals

Area of Science:

• Microbiology
• Biogeochemistry
• Mineralogy

Background:

• Microbial biomineralization drives global biogeochemical cycles.
• Intracellular calcification is common in eukaryotes but rare in prokaryotes.
• Magnetotactic bacteria (MTB) were previously not known to form intracellular carbonates.

Purpose of the Study:

• To investigate intracellular biomineralization in magnetotactic bacteria (MTB).
• To identify the diversity and genetic basis of prokaryotic intracellular calcification.
• To explore the role of MTB in trace metal cycling.

Main Methods:

• Comparative genomic analyses of MTB.
• Electron microscopy to visualize carbonate granules.
• Metagenomic and structural protein modeling to understand metal transport.

Main Results:

• Three ecotypes of MTB from Pseudomonadota and Nitrospirota phyla form intracellular carbonate granules.
• These granules are enriched in Ba, Mg, and Ni.
• MTB possess multiple metal-permease systems potentially involved in cation uptake and precipitation.

Conclusions:

• This study expands the known diversity of prokaryotic intracellular calcifiers.
• MTB may play a significant role in the biogeochemical cycling of heavy metals like Ba and Ni.
• Intracellular calcification might be a more widespread bacterial trait than previously assumed.