Transformation of crustacean pathogenic bacterium Spiroplasma eriocheiris and expression of yellow fluorescent protein

•A transformation method is developed for Spiroplasma eriocheiris.•The transformation is achieved using oriC plasmid haboring S. eriocheiris specific promoters.•Fluorescent protein useful for protein tagging is expressed in S. eriocheiris.•Methods developed here should be useful to identify genes involved in swimming and trace those proteins.

Spiroplasma eriocheiris, the cause of crab trembling disease, is a wall-less bacterium, related to Mycoplasmas, measuring 2.0-10.0 μm long. It features a helical cell shape and a unique swimming mechanism that does not use flagella; instead, it moves by switching the cell helicity at a kink traveling from the front to the tail. S. eriocheiris seems to use a novel chemotactic system that is based on the frequency of reversal swimming behaviors rather than the conventional two-component system, which is generally essential for bacterial chemotaxis. To identify the genes involved in these novel mechanisms, we developed a transformation system by using oriC plasmid harboring the tetracycline resistant gene, tetM, which is under the control of a strong promoter for an abundant protein, elongation factor-Tu. The transformation efficiency achieved was 1.6 × 10−5 colony forming unit (CFU) for 1 μg DNA, enabling the expression of the enhanced yellow fluorescent protein (EYFP).