JB Accepts, published online ahead of print on 30 October 2009

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J. Bacteriol. doi:10.1128/JB.00716-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Inefficient Tat-Dependent Export of Periplasmic Amidases in an Escherichia coli Strain with Mutations in Two DedA Family Genes.

Rakesh Sikdar and William T. Doerrler^*

Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803

^* To whom correspondence should be addressed. Email: wdoerr{at}lsu.edu.

The DedA family genes are found in most bacterial genomes. Two of these proteins include Escherichia coli YqjA and YghB, predicted inner membrane proteins of unknown function sharing 61% amino acid identity. The single deletion mutants in Escherichia coli are largely without phenotype, but the double mutant (BC202; yqjA::tet^R, yghB::kan^R) is characterized by incomplete cell division, temperature sensitivity and altered phospholipid levels (J Bacteriol 190, 4489. 2008). In this report, we have better characterized the cell division chaining defect of BC202. Fluorescence recovery after photobleaching (FRAP) indicates that 58% of the cells in chains are compartmentalized by at least a cytoplasmic membrane. GFP fusions to the cell-division proteins FtsZ, ZipA, FtsI, FtsL and FtsQ are correctly localized to new septation sites in BC202. Periplasmic amidases AmiC and AmiA, secreted by the twin arginine transport (Tat) pathway, are localized to the cytoplasm in BC202. Overexpression of AmiA, AmiC or AmiB, a periplasmic amidase secreted via the general secretory pathway, restores normal cell division but does not suppress the temperature sensitivity of BC202 indicating that YghB and YqjA may play additional roles in cellular physiology. Strikingly, overexpression of the Tat export machinery (TatABC) results in both normal cell division and growth at elevated temperatures. These data collectively suggest that the twin arginine pathway functions inefficiently in BC202, likely due to the altered levels of membrane phospholipids in this mutant. These results underscore the importance of membrane composition in the proper function of the Tat protein export pathway.