Previously uncharacterized rectangular bacterial structures in the dolphin mouth

Dudek et al. describe rectangular bacterial structures in the mouths of dolphins. Using various genomic and microscopy techniques, they show that the structures consist of bacterial cells that appear to divide along the longitudinal axis and display other unusual features. Much remains to be explored regarding the diversity of uncultured, host-associated microbes. Here, we describe rectangular bacterial structures (RBSs) in the mouths of bottlenose dolphins. DNA staining revealed multiple paired bands within RBSs, suggesting the presence of cells dividing along the longitudinal axis. Cryogenic transmission electron microscopy and tomography showed parallel membrane-bound segments that are likely cells, encapsulated by an S-layer-like periodic surface covering. RBSs displayed unusual pilus-like appendages with bundles of threads splayed at the tips. We present multiple lines of evidence, including genomic DNA sequencing of micromanipulated RBSs, 16S rRNA gene sequencing, and fluorescence in situ hybridization, suggesting that RBSs are bacterial and distinct from the genera Simonsiella and Conchiformibius (family Neisseriaceae), with which they share similar morphology and division patterning. Our findings highlight the diversity of novel microbial forms and lifestyles that await characterization using tools complementary to genomics such as microscopy.

Automated summary

Dudek et al. identified rectangular bacterial structures in the mouths of dolphins. These structures consist of bacterial cells that divide along the longitudinal axis and display unique features. This discovery highlights the need for further exploration of uncultured, host-associated microbes.