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Volume 171, Issue 5

The Fsr transporter of contributes to antimicrobial resistance and symbiosis with alfalfa Open Access

Abstract

Major facilitator superfamily (MFS) transporters in bacteria participate in both the uptake and export of ions, metabolites or toxic compounds. In rhizobia, specific MFS transporters increase resistance to plant-produced compounds and may also affect other phenotypic traits, including symbiosis with legume host plants. Here, we describe the importance of the 1021 Fsr efflux pump in resistance to selected antimicrobial compounds and in modulating biofilm formation, motility and symbiotic efficiency with alfalfa. The gene () is annotated as encoding an MFS family fosmidomycin efflux pump. Unexpectedly, both the 1021 wild type and an null mutant were highly resistant to fosmidomycin. Our assays indicate that this is due to an inability to transport the antibiotic. Unlike the wild type, the mutant was highly sensitive to the fosmidomycin structural analogue fosfomycin, and moderately more sensitive to hydrogen peroxide (HO) and deoxycholate (DOC). Root and seed exudates from alfalfa did not inhibit the growth of the wild type or mutant. transcription significantly increased proportionally to the concentration of fosfomycin added to cultures but was unaffected by the addition of other antibiotics, HO, DOC or SDS. Alfalfa seed exudate moderately increased transcriptional expression. Fluorometric assays using ethidium bromide as a substrate and carbonyl cyanide m-chlorophenyl hydrazone as an energy decoupler showed that Fsr was a proton-dependent efflux pump. Biofilm formation and swimming motility were decreased and increased, respectively, in the mutant, and its symbiotic efficiency with alfalfa was decreased in terms of nodule numbers per plant and plant dry weights.

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Keyword(s): antibiotic efflux pumps , antibiotic resistance , biofilm formation , fosmidomycin , Sinorhizobium meliloti–alfalfa symbiosis and swimming motility
Funding
This study was supported by the:
  • Dirección General de Asuntos del Personal Académico, Universidad Nacional Autónoma de México (Award IN208823)
    • Principal Award Recipient: LourdesGirard
  • Dirección General de Asuntos del Personal Académico, Universidad Nacional Autónoma de México (Award IN207620)
    • Principal Award Recipient: MichaelF. Dunn
  • Dirección General de Asuntos del Personal Académico, Universidad Nacional Autónoma de México (Award IN206317)
    • Principal Award Recipient: MichaelF. Dunn
© 2025 The Authors
  • This is an open-access article distributed under the terms of the Creative Commons Attribution License. This article was made open access via a Publish and Read agreement between the Microbiology Society and the corresponding author’s institution.
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2025-05-21
2026-04-17

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The Fsr transporter of Sinorhizobium meliloti contributes to antimicrobial resistance and symbiosis with alfalfa
Microbiology 171, 001566 (2025); https://doi.org/10.1099/mic.0.001566
/content/journal/micro/10.1099/mic.0.001566
/content/journal/micro/10.1099/mic.0.001566
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