Giant multicellular magnetotactic prokaryotes in marine sediments

Area of Science:

• Microbiology
• Marine Biology
• Evolutionary Biology

Background:

• Multicellular magnetotactic prokaryotes are marine bacteria that use ferrimagnetic nanocrystals for navigation.
• Previously, only spherical and ellipsoidal morphotypes, around 3-6 μm and composed of ~50 cells, were known.
• These bacteria belong to three genera within the Desulfobacterota phylum and inhabit reduced marine sediments.

Purpose of the Study:

• To report the discovery of a novel, significantly larger morphotype of multicellular magnetotactic prokaryotes.
• To investigate the cell ultrastructure, ecological niche, and physiology of this new morphotype.
• To determine the phylogenetic placement of these giant bacteria.

Main Methods:

• Magnetic enrichment techniques were employed to isolate the bacteria.
• Transmission electron microscopy and confocal microscopy were used to examine cell ultrastructure.
• Single-consortium genomics and phylogenomic analyses were performed for classification.

Main Results:

• A new morphotype of giant multicellular magnetotactic prokaryotes, approximately 30 times larger than previously known forms, was identified in the Mediterranean Sea.
• These consortia contain an average of 130 cells, with each cell producing over 100 greigite magnetosomes.
• Phylogenomic analyses placed these bacteria in a new genus and species, Magnetogigantoglobus mediterraneus, within the Candidatus Magnetomoraceae family.

Conclusions:

• The discovery of Magnetogigantoglobus mediterraneus expands the known diversity of multicellular magnetotactic prokaryotes.
• These giant bacteria, despite genetic divergence and different ultrastructure, share physiological traits like sulfate reduction with other morphotypes.
• The findings contribute to understanding the evolution of multicellularity and magnetotaxis in prokaryotes.