Abstract
To adapt to changing environmental niches, bacteria require taxis, a movement toward or away from a stimulus (ligand). Chemotaxis has been studied in some members of the Soft Rot Pectobacteriaceae (SRP), particularly members of the genus Dickeya. On the contrary, there are fewer studies on this topic for the other genus in the SRP group, namely Pectobacterium. This study evaluated chemotactic responses in Pectobacterium brasiliense (Pb 1692) to various ligands. A total of 34 methyl-accepting chemotactic proteins (MCPs) were identified in the Pb 1692 genome and the domain architectures of these MCPs were determined. Four Pb 1692 MCPs previously shown to be differentially expressed during potato tuber infection were selected for further functional characterization. Toward this end, Pb 1692 mutant strains each lacking either AED-0001492, AED-0003671, AED-0000304, or AED-0000744 were generated. Two of these mutants (AED-0001492 and AED-0003671), were attenuated in their ability to grow and respond to citrate and are thus referred to as MCPcit2 and MCPcit1, respectively, while the other two, AED-0000304 (MCPxyl) and AED-0000744 (MCPasp), were affected in their ability to respond to xylose and aspartate, respectively. Trans-complementation of the mutant strains restored swimming motility in the presence of respective ligands. The four MCP mutants were not affected in virulence but were significantly attenuated in their ability to attach to potato leaves suggesting that ecological fitness is an important contribution of these MCPs toward Pb 1692 biology.
Highlights
Bacteria employ a myriad of mechanisms to efficiently adapt to changing environmental conditions (Armitage, 1992; Blair, 1995)
In vitro growth and virulence in potato tubers indicated that the mutant strains and Pb 1692 wild-type strain had no significant difference (Supplementary Figures 4A,B). These findings demonstrate that in planta and in vitro growth as well as virulence on potato tubers are not affected by deletion of these selected methyl-accepting chemotaxis proteins (MCPs)-encoding genes in Pb 1692
Chemotaxis plays an important role in phytopathogenic bacteria host colonization, infection, and disease development
Summary
Bacteria employ a myriad of mechanisms to efficiently adapt to changing environmental conditions (Armitage, 1992; Blair, 1995). Such pieces of machinery include one-component systems (OCS), two-component systems (TCS), and chemoreceptor-based signaling, known as chemotaxis (Matilla and Krell, 2017). Chemotaxis and motility are critical during the early stages of infection when bacteria search for entry sites to penetrate the host apoplast (Stock and Baker, 2009; Reverchon and Nasser, 2013). The attracted bacteria swim toward a wounded site to which they attach and subsequently enter the host apoplastic environment (Antúnez-Lamas et al, 2009a). Unlike E. coli, many plant pathogens are predicted to encode more than 30 MCP receptors; with different Pectobacterium spp. encoding between 30 and 39 taxis receptors (Glasner et al, 2008)
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