Chemotaxis without Conventional Two-Component System, Based on Cell Polarity and Aerobic Conditions in Helicity-Switching Swimming of Spiroplasma eriocheiris.

Peng Liu,Shengyue Wang,Daisuke Nakane,Wen Wang,Makoto Miyata,Guoping Zhao,Huajun Zheng,Wei Gu,Natsuho Terahara,Qingguo Meng

doi:10.3389/fmicb.2017.00058

Abstract

Spiroplasma eriocheiris is a pathogen that causes mass mortality in Chinese mitten crab, Eriocheir sinensis. S. eriocheiris causes tremor disease and infects almost all of the artificial breeding crustaceans, resulting in disastrous effects on the aquaculture economy in China. S. eriocheiris is a wall-less helical bacterium, measuring 2.0 to 10.0 μm long, and can swim up to 5 μm per second in a viscous medium without flagella by switching the cell helicity at a kink traveling from the front to the tail. In this study, we showed that S. eriocheiris performs chemotaxis without the conventional two-component system, a system commonly found in bacterial chemotaxis. The chemotaxis of S. eriocheiris was observed more clearly when the cells were cultivated under anaerobic conditions. The cells were polarized as evidenced by a tip structure, swimming in the direction of the tip, and were shown to reverse their swimming direction in response to attractants. Triton X-100 treatment revealed the internal structure, a dumbbell-shaped core in the tip that is connected by a flat ribbon, which traces the shortest line in the helical cell shape from the tip to the other pole. Sixteen proteins were identified as the components of the internal structure by mass spectrometry, including Fibril protein and four types of MreB proteins.

Highlights

Spiroplasma is a genus of bacteria that belongs to the class Mollicutes, which includes groups of economically important pathogens, such as the Mycoplasma and Phytoplasma species
To identify proteins related to the conventional two-component system (TCS) in the genome, a homology search against all the “Prokaryotic 2-Component System” (P2CS) database (Barakat et al, 2011) was firstly performed
We analyzed all of the domains encoded by the genome, and failed to find any known domains of histidine kinases (HKs), response regulators (RRs), and other protein components that are involved in well-studied chemotaxis systems, like Methylaccepting chemotaxis protein (MCP) signaling domain

Summary

Introduction

Spiroplasma is a genus of bacteria that belongs to the class Mollicutes, which includes groups of economically important pathogens, such as the Mycoplasma and Phytoplasma species. These bacteria are characterized by small genomes and the lack of a peptidoglycan layer (Davis et al, 1972; Daniels et al, 1980; Daniels and Longland, 1984; Trachtenberg, 1998). Spiroplasma Swimming genomes reported so far do not have orthologs of other bacterial motility systems but have five to seven homologs of the protein MreB (Table S1; Ku et al, 2013, 2014; Lo et al, 2015; Davis et al, 2015a,b). Two filamentous proteins have been identified including Fibril and MreB (Williamson et al, 1991; Trachtenberg et al, 2008), the whole image of the internal structure is still unclear

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Discussion

Conclusion