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Involvement of the azorhizobial chromosome partition gene (parA) in the onset of bacteroid differentiation during Sesbania rostrata stem nodule development.

ABSTRACT: A parA gene in-frame deletion mutant of Azorhizobium caulinodans ORS571 (ORS571-?parA) was constructed to evaluate the roles of the chromosome-partitioning gene on various bacterial traits and on the development of stem-positioned nodules. The ?parA mutant showed a pleiomorphic cell shape phenotype and was polyploid, with differences in nucleoid sizes due to dramatic defects in chromosome partitioning. Upon inoculation of the ?parA mutant onto the stem of Sesbania rostrata, three types of immature nodule-like structures with impaired nitrogen-fixing activity were generated. Most showed signs of bacteroid early senescence. Moreover, the ?parA cells within the nodule-like structures exhibited multiple developmental-stage phenotypes. Since the bacA gene has been considered an indicator for bacteroid formation, we applied the expression pattern of bacA as a nodule maturity index in this study. Our data indicate that the bacA gene expression is parA dependent in symbiosis. The presence of the parA gene transcript was inversely correlated with the maturity of nodule; the transcript was switched off in fully mature bacteroids. In summary, our experimental evidence demonstrates that the parA gene not only plays crucial roles in cellular development when the microbe is free-living but also negatively regulates bacteroid formation in S. rostrata stem nodules.

SUBMITTER: Liu CT

PROVIDER: S-EPMC3127717 | biostudies-literature | 2011 Jul

REPOSITORIES: biostudies-literature

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Involvement of the azorhizobial chromosome partition gene (parA) in the onset of bacteroid differentiation during Sesbania rostrata stem nodule development.

Liu Chi-Te CT Lee Kyung-Bum KB Wang Yu-Sheng YS Peng Min-Hua MH Lee Kung-Ta KT Suzuki Shino S Suzuki Tadahiro T Oyaizu Hiroshi H

Applied and environmental microbiology 20110513 13

A parA gene in-frame deletion mutant of Azorhizobium caulinodans ORS571 (ORS571-ΔparA) was constructed to evaluate the roles of the chromosome-partitioning gene on various bacterial traits and on the development of stem-positioned nodules. The ΔparA mutant showed a pleiomorphic cell shape phenotype and was polyploid, with differences in nucleoid sizes due to dramatic defects in chromosome partitioning. Upon inoculation of the ΔparA mutant onto the stem of Sesbania rostrata, three types of immatu ...[more]

PMID: 21571889

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Project description:UnlabelledAzorhizobium caulinodans ORS571 is a free-living nitrogen-fixing bacterium which can induce nitrogen-fixing nodules both on the root and the stem of its legume host Sesbania rostrata This bacterium, which is an obligate aerobe that moves by means of a polar flagellum, possesses a single chemotaxis signal transduction pathway. The objective of this work was to examine the role that chemotaxis and aerotaxis play in the lifestyle of the bacterium in free-living and symbiotic conditions. In bacterial chemotaxis, chemoreceptors sense environmental changes and transmit this information to the chemotactic machinery to guide motile bacteria to preferred niches. Here, we characterized a chemoreceptor of A. caulinodans containing an N-terminal PAS domain, named IcpB. IcpB is a soluble heme-binding protein that localized at the cell poles. An icpB mutant strain was impaired in sensing oxygen gradients and in chemotaxis response to organic acids. Compared to the wild-type strain, the icpB mutant strain was also affected in the production of extracellular polysaccharides and impaired in flocculation. When inoculated alone, the icpB mutant induced nodules on S. rostrata, but the nodules formed were smaller and had reduced N2-fixing activity. The icpB mutant failed to nodulate its host when inoculated competitively with the wild-type strain. Together, the results identify chemotaxis and sensing of oxygen by IcpB as key regulators of the A. caulinodans-S. rostrata symbiosis.ImportanceBacterial chemotaxis has been implicated in the establishment of various plant-microbe associations, including that of rhizobial symbionts with their legume host. The exact signal(s) detected by the motile bacteria that guide them to their plant hosts remain poorly characterized. Azorhizobium caulinodans ORS571 is a diazotroph that is a motile and chemotactic rhizobial symbiont of Sesbania rostrata, where it forms nitrogen-fixing nodules on both the roots and the stems of the legume host. We identify here a chemotaxis receptor sensing oxygen in A. caulinodans that is critical for nodulation and nitrogen fixation on the stems and roots of S. rostrata These results identify oxygen sensing and chemotaxis as key regulators of the A. caulinodans-S. rostrata symbiosis.

Dataset Information

Involvement of the azorhizobial chromosome partition gene (parA) in the onset of bacteroid differentiation during Sesbania rostrata stem nodule development.

Publications

Involvement of the azorhizobial chromosome partition gene (parA) in the onset of bacteroid differentiation during Sesbania rostrata stem nodule development.

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