Identification and Characterization of Rothia amarae sp. nov. in a Suspension Culture of Arabidopsis thaliana (Heynh.) Cells

We report for the first time that a nonpathogenic bacterial microflora has been found in a suspension culture of Arabidopsis thaliana cells. The 16S rRNA gene sequencing showed that the isolate belonged to Rothia amarae. Identification was confirmed by microbiological, microscopic, and immunochemical methods. Growth of the isolate on blood agar preserves the morphological and immunochemical properties of the isolate from the plant cell suspension culture. Whether the isolated strain is a contaminant or a true symbiont remains an open question. It is known that Rothia bacteria live mostly in oceanic and waste water and in benthos. Members of Rothia are part of the normal microflora of the oral cavity, respiratory tract, and stomach of humans. Rothia bacteria have also been detected as endophytes in association with associated with Magellan sphagnum (Sphagnum magellanicum Brid.), stellate pohostemon (Dysophylla stellata (Lour.) Benth.), pointed banana (Musa acuminate Colla), and alder (Alnus). Endophytic Rothia are inhibitory against several pathogenic fungi and bacteria. In addition, some actinobacteria, including members of Rothia, are nitrogen fixers. It cannot be ruled out that the R. amarae strain isolated in this work can be endosymbiotic with a suspension culture of A. thaliana. The bacterial “inclusions” found by us in a suspension culture of A. thaliana merit further investigation to identify them more deeply and clarify their symbiotic properties.