Abstract
The translocation and assembly module (TAM) in bacteria consists of TamA and TamB that form a complex to control the transport and secretion of outer membrane proteins. Herein, we demonstrated that the DR_1462-DR_1461-DR_1460 gene loci on chromosome 1 of Deinococcus radiodurans, which lacks tamA homologs, is a tamB homolog (DR_146T) with two tamB motifs and a DUF490 motif. Mutation of DR_146T resulted in cell envelope peeling and a decrease in resistance to shear stress and osmotic pressure, as well as an increase in oxidative stress resistance, consistent with the phenotype of a surface layer (S-layer) protein SlpA (DR_2577) mutant, demonstrating the involvement of DR_146T in maintenance of cell envelope integrity. The 123 kDa SlpA was absent and only its fragments were present in the cell envelope of DR_146T mutant, suggesting that DR_146T might be involved in maintenance of the S-layer. A mutant lacking the DUF490 motif displayed only a slight alteration in phenotype compared with the wild type, suggesting DUF490 is less important than tamB motif for the function of DR_146T. These findings enhance our understanding of the properties of the multilayered envelope in extremophilic D. radiodurans, as well as the diversity and functions of TAMs in bacteria.
Highlights
Mitomycin C (MMC)[19,20,21,22]
Two neighbouring sequences (DR_1462 and DR_1461) each containing a tamB motif were identified in the D. radiodurans genome using BLASTP, with each sequence sharing 28% and 29% amino acid sequence identity with Escherichia coli (E. coli) TamB encoded by b4221, respectively
A TamA homolog was not detected in D. radiodurans using the E. coli TamA as the query sequence, suggesting D. radiodurans might express a specific translocation and assembly module (TAM) lacking TamA
Summary
It is widely accepted that efficient DNA repair systems and cell defence systems including an unusual cell envelope and small molecule antioxidants (e.g. Mn2+ and carotenoids) contribute to the survival of D. radiodurans under various stresses[20,23,24,25,26,27,28]. D. radiodurans has an unusual multilayered cell envelope that includes a thick peptidoglycan cell wall, an outer membrane-like lipid layer and a S-layer, and it reacts positively with Gram stain despite sharing some characteristics with Gram-negative bacteria[24,29,30]. The SlpA (DR_2577) is the pivotal component of the S-layer of D. radiodurans. Survival assays and cell envelope proteome analysis were performed to investigate the roles of DR_146T in cell envelope integrity with respect to SlpA and stress resistance
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