Abstract
Spatial organization of chemotactic proteins is important for cooperative response to external stimuli. However, factors affecting the localization dynamics of chemotaxis proteins are less studied. According to some reports, the polar localization of chemotaxis system I is induced by hypoxia and starvation in Vibrio cholerae. However, in V. cholerae, the chemotaxis system I is not involved in flagellum-mediated chemotaxis, and it may play other alternative cellular functions. In this study, we found that the polar localization of CheZ, a phosphatase regulating chemotactic movement in Azorhizobium caulinodans ORS571, can also be affected by hypoxia and cellular energy-status. The conserved phosphatase active site D165 and the C-terminus of CheZ are essential for the energy-related localization, indicating a cross link between hypoxia-related localization changes and phosphatase activity of CheZ. Furthermore, three of five Aer-like chemoreceptors containing PAS domains participate in the cellular localization of CheZ. In contrast to carbon starvation, free-living nitrogen fixation can alleviate the role of nitrogen limitation and hypoxia on polar localization of CheZ. These results showed that the localization changes induced by hypoxia might be a strategy for bacteria to adapt to complex environment.
Highlights
Azorhizobium caulinodans ORS571 is an alpha-Proteobacterium that can fix atmospheric nitrogen in free-living conditions or inside nodules formed on root or stem of the tropical legume Sesbania rostrata (Dreyfus and Dommergues, 1981; Dreyfus et al, 1988)
Nitrogen limiting conditions are involved in the polar localization of CheZ. These results indicated that the fluctuation of subcellular localization of chemotaxis proteins might be an important strategy for bacteria to respond to environmental stimulus
We previously reported that CheZ in A. caulinodans can locate to cell poles and the localization pattern of CheZ is diverse, including monopolar, bipolar, and diffuse (Liu et al, 2020)
Summary
Azorhizobium caulinodans ORS571 is an alpha-Proteobacterium that can fix atmospheric nitrogen in free-living conditions or inside nodules formed on root or stem of the tropical legume Sesbania rostrata (Dreyfus and Dommergues, 1981; Dreyfus et al, 1988). Chemotaxis and motility provide a fitness advantage for A. caulinodans ORS571 during host colonization and allows for adaptation to harsh environment (Jiang et al, 2016a; Liu et al, 2017, 2018a,b, 2019; Sun et al, 2019). The chemotaxis signaling pathway has been well studied in Escherichia coli (Wadhams and Armitage, 2004). Transmembrane methyl-accepting chemotaxis proteins (MCPs) are responsible for sensing external stimuli.
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