Characterization of the Sinorhizobium meliloti HslUV and ClpXP Protease Systems in Free-Living and Symbiotic States

Journal Article · 22 January 2019 · Journal of Bacteriology

DOI: https://doi.org/10.1128/jb.00498-18 · OSTI ID:1614598

Ogden, Aaron J.  ^[1]; McAleer, Jacqueline M. ^[1]; Kahn, Michael L. ^[1]; Becker, Anke ^[1]

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1. Washington State Univ., Pullman, WA (United States)

Symbiotic nitrogen fixation (SNF) in the interaction between the soil bacteria Sinorhizobium meliloti and legume plant Medicago sativa is carried out in specialized root organs called nodules. During nodule development, each symbiont must drastically alter their proteins, transcripts, and metabolites in order to support nitrogen fixation. Moreover, bacteria within the nodules are under stress, including challenges by plant antimicrobial peptides, low pH, limited oxygen availability, and strongly reducing conditions, all of which challenge proteome integrity. S. meliloti stress adaptation, proteome remodeling, and quality control are controlled in part by the large oligomeric protease complexes HslUV and ClpXP1. To improve understanding of the roles of S. meliloti HslUV and ClpXP1 under free-living conditions and in symbiosis with M. sativa, we generated ΔhslU, ΔhslV, ΔhslUV, and ΔclpP1 knockout mutants. The shoot dry weight of M. sativa plants inoculated with each deletion mutant was significantly reduced, suggesting a role in symbiosis. Further, slower free-living growth of the ΔhslUV and ΔclpP1 mutants suggests that HslUV and ClpP1 were involved in adapting to heat stress, the while ΔhslU and ΔclpP1 mutants were sensitive to kanamycin. All deletion mutants produced less exopolysaccharide and succinoglycan, as shown by replicate spot plating and calcofluor binding. We also generated endogenous C-terminal enhanced green fluorescent protein (eGFP) fusions to HslU, HslV, ClpX, and ClpP1 in S. meliloti. Using anti-eGFP antibodies, native coimmunoprecipitation experiments with proteins from free-living and nodule tissues were performed and analyzed by mass spectrometry. The results suggest that HslUV and ClpXP were closely associated with ribosomal and proteome quality control proteins, and they identified several novel putative protein-protein interactions.

• Research Organization: Washington State Univ., Pullman, WA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: FG03-96ER20225
• OSTI ID: 1614598
• Journal Information: Journal of Bacteriology, Vol. 201, Issue 7; ISSN 0021-9193
• Publisher: American Society for MicrobiologyCopyright Statement
• Country of Publication: United States
• Language: English