Archives of Microbiology

, Volume 192, Issue 7, pp 595–602 | Cite as

A high-conductance cation channel from the inner membrane of the free-living soil bacteria Rhizobium etli

  • Daniel BallezaEmail author
  • Carmen Quinto
  • David Elias
  • Froylán Gómez-LagunasEmail author
Short Communication


In this communication we reported the study of a cation channel present in the cytoplasmic membrane of the nitrogen fixing bacterium Rhizobium etli. Inner-membrane (IM) vesicles were purified and fused into planar lipid bilayers (PLBs), under voltage clamp conditions. We have found that fusion of IM-enriched vesicle fractions with these model membranes leads, mainly (>30% of 46 experiments), to the reconstitution of high-conductance channels. Following this strategy, the activity of a channel with main open conductance of 198 pS, in symmetrical 100 mM KCl, was recorded. The single-channel conductance increase to 653 pS in the presence of a 5:1 (cis to trans) gradient of KCl. The channel exhibits voltage dependency and a weak selectivity for cations showing a permeability ratios of P Rb/P K = 0.96, P Na/P K = 0.07, and a conductance ratio of γRbK = 1.1. The channel here characterized represents a previously undescribed Rhizobium channel although its precise role in rhizobial physiology remains yet to be determined.


Rhizobium Ion channels Permeation 



We thank Guadalupe Zavala for her excellent technical assistance with electron microscopy and to Karla García y García for helping us with database searching using RetliDB. This work was supported by Grants CONACyT 56631 and DGAPA IN204907 to C.Q. and CONACyT 60313 and DGAPA IN222208 to F.G.L. D. Balleza thanks to DGAPA-UNAM for a postdoctoral fellowship. We sincerely thank the reviewers for their insightful comments and suggestions.

Supplementary material

203_2010_587_MOESM1_ESM.tif (985 kb)
Fig. S1. Sequence alignment of the putative transmembrane domains of the two proteins with similarity to K+ channels from R. etli (ABC91945 and YP467785), the cyclic nucleotide-regulated channel MlotiK1 (M. loti, Q98GN8), KvAp (Aeropyrum pernix, BAA79939), KcsA (Streptomyces lividans, CAA86025), Kv channel Shaker (Drosophila melanogaster, P08510), and RatKv2.1 (Rattus norvegicus, P15387). The secondary structure of Shaker is indicated. In sequences of prokaryotic and eukaryotic Kv channels, regions of high homology are coloured in grey, positively charged amino acids in S4 are in yellow whereas identical residues are in black boxes. Alignment was made with ClustalW followed by manual adjustment and exclusion of loops (TIFF 985 kb)


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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  1. 1.Departamento de Biología Molecular de PlantasInstituto de Biotecnología, UNAMCuernavacaMexico
  2. 2.Departamento de FisiologíaBiofísica y Neurociencias. CINVESTAV-IPNMexico CityMexico
  3. 3.Facultad de Medicina, Departamento de FisiologíaUNAM. México. Cd. UniversitariaMéxico, D.F.Mexico
  4. 4.Unidad de Biofísica, CSIC-UPV/EHUUniversidad del País VascoLeioaSpain

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