Examination of the Global Regulon of CsrA in subsp. Using Quantitative Proteomics and Other Approaches.

The RNA-binding protein CsrA is a global posttranscriptional regulator and controls many physiological processes and virulence traits. Deletion of caused loss of virulence, reduced motility and production of xanthan gum and substantial increase in glycogen accumulation, as well as enhanced bacterial aggregation and cell adhesion in spp. How CsrA controls these traits is poorly understood. In this study, an isobaric tag for relative and absolute quantitation (iTRAQ)-based proteomic analysis was conducted to compare the protein profile of wild-type strain subsp. and the isogenic Δ strain. A total of 2,374 proteins were identified, and 284 were considered to be differentially expressed proteins (DEP), among which 151 proteins were up-regulated and 133 were down-regulated in the Δ strain with respect to the wild-type strain. Enrichment analysis and a protein-protein interaction network analysis showed that CsrA regulates bacterial secretion systems, flagella, and xanthan gum biosynthesis. Several proteins encoded by the operon were down-regulated, whereas proteins associated with flagellum assembly and the type IV secretion system were up-regulated in the Δ strain relative to the Xcc306 strain. These results were confirmed by β-glucuronidase assay or Western blot. RNA secondary structure prediction and a gel-shift assay indicated that CsrA binds to the Shine-Dalgarno sequence of . In addition, the iTRAQ analysis identified 248 DEPs that were not previously identified in transcriptome analyses. Among them, CsrA regulates levels of eight regulatory proteins (ColR, GacA, GlpR, KdgR, MoxR, PilH, RecX, and YgiX), seven TonB-dependent receptors, four outer membrane proteins, and two ferric enterobactin receptors. Taken together, this study greatly expands understanding of the regulatory network of CsrA in subsp. .[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.