Abstract
The ancient bacterial lineage Thermus spp has a primitive form of outer membrane attached to the cell wall through SlpA, a protein that shows intermediate properties between S-layer proteins and outer membrane (OM) porins. In E. coli and related Proteobacteria, porins are secreted through the BAM (β-barrel assembly machinery) pathway, whose main component is BamA. A homologue to this protein is encoded in all the Thermus spp so far sequenced, so we wondered if this pathway could be responsible for SlpA secretion in this ancient bacterial model. To analyse this hypothesis, we attempted to get mutants on this BamAth of T. thermophilus HB27. Knockout and deletion mutants lacking the last 10 amino acids were not viable, whereas its depletion by means of a BamA antisense RNA lead defective attachment to the cell wall of its OM-like envelope. Such defects were related to defective folding of the SlpA protein that was more sensitive to proteases than in a wild-type strain. A similar phenotype was found in mutants lacking the terminal Phe of SlpA. Further protein–protein interaction assays confirmed the existence of specific binding between SlpA and BamAth. Taking together, these data suggest that SlpA is secreted through a BAM-like pathway in this ancestral bacterial lineage, supporting an ancient origin of this pathway before the evolution of the Proteobacteria.
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Acknowledgments
This work has been supported by grant BIO2010-18875 from the Spanish Ministry of Science. An institutional grant from Fundación Ramón Areces to CBMSO is acknowledged. F. Acosta was funded by a FPI fellowship from the Ministry of Education. We thank Jutta Nesper for providing the antiserum against the BamAth protein and L.A. Fernández-Herrero for critical reading of this work.
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Communicated by S. Albers.
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Acosta, F., Ferreras, E. & Berenguer, J. The β-barrel assembly machinery (BAM) is required for the assembly of a primitive S-layer protein in the ancient outer membrane of Thermus thermophilus . Extremophiles 16, 853–861 (2012). https://doi.org/10.1007/s00792-012-0480-x
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DOI: https://doi.org/10.1007/s00792-012-0480-x