Previously uncharacterized rectangular bacterial structures in the dolphin mouth.

Area of Science:

• Microbiology
• Marine Biology
• Microbial Ecology

Background:

• The diversity of uncultured, host-associated microbes remains largely unexplored.
• Novel microbial forms and lifestyles require advanced characterization techniques.

Purpose of the Study:

• To describe the morphology and characteristics of previously undocumented rectangular bacterial structures (RBSs) found in bottlenose dolphin oral cavities.
• To determine the taxonomic and phylogenetic placement of these novel bacterial structures.

Main Methods:

• Cryogenic transmission electron microscopy and tomography for high-resolution structural analysis.
• Genomic DNA sequencing of micromanipulated RBSs and 16S rRNA gene sequencing for phylogenetic identification.
• Fluorescence in situ hybridization (FISH) to confirm bacterial identity and localization.

Main Results:

• Rectangular bacterial structures (RBSs) with parallel, membrane-bound segments resembling cells were observed.
• RBSs possess unique pilus-like appendages and are encapsulated by an S-layer-like covering.
• Genomic and phylogenetic analyses indicate RBSs are bacteria distinct from the Neisseriaceae family, including Simonsiella and Conchiformibius.

Conclusions:

• The discovery of RBSs highlights the existence of novel microbial forms and lifestyles in host-associated environments.
• These findings underscore the importance of complementary approaches, such as advanced microscopy alongside genomics, for microbial discovery.