Proteomic and transcriptomic characterization of a virulence-deficient phosphatidylcholine-negative Agrobacterium tumefaciens mutant
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Phosphatidylcholine (PC) is the most abundant phospholipid in eukaryotic membranes, whereas only a limited number of bacteria are able to synthesize PC. Intriguingly, many of the bacteria with PC-containing membranes interact with eukaryotic hosts. PC is one of the major membrane lipids in the phytopathogenic bacterium Agrobacterium tumefaciens. The presence of PC is critical for diverse cellular processes like motility, biofilm formation, stress resistance, and virulence. The exact role of PC in these processes is unknown. Here, we examined the global consequences of the complete loss of PC at the proteomic and transcriptomic levels. Both strategies validated the impaired virulence gene induction responsible for the virulence defect of the PC-deficient mutant. In addition, the proteomic approach revealed a limited subset of proteins with altered abundance including the reduced flagellar proteins FlaA and FlaB, which explains the motility defect of the PC mutant. At the whole-genome level, the loss of PC was correlated with altered expression of up to 13% of all genes, most encoding membrane or membrane-associated proteins and proteins with functions in the extracytoplasmic stress response. Our integrated analysis revealed that A. tumefaciens dynamically remodels its membrane protein composition in order to sustain normal growth in the absence of PC.
KeywordsMembrane lipids Phosphatidylcholine α-Proteobacterium Agrobacterium Plant–microbe interaction
We are grateful to Knut Büttner (Greifswald) for MALDI-MS analyses, Hauke Hennecke and co-workers (Zürich) for providing access to the GeneSpring gene expression analysis software, Birgit Scharf (Blacksburg, Virginia) for antiflagella sera, and Christian Baron (Montreal) for VirB9 antisera. We thank Yi-Chun Chen (Taipei) for constructing pAC01-virBp and pAC01-tzsp, Meriyem Aktas and Sina Langklotz for helpful comments on this manuscript, and Christiane Fritz for technical assistance. The work was in part supported by a grant the German Research Foundation (DFG NA 240/7) to FN, a grant from Taiwan National Science Council (NSC 95-2320-B-001-009) to EML and a joint grant from the German Academic Exchange Service (DAAD) and the Taiwan National Science Council (PPP grant no. 0970029248P) to FN and EML.
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