NorM, an Erwinia amylovora Multidrug Efflux Pump Involved in In Vitro Competition with Other Epiphytic Bacteria

Abstract

Blossoms are important sites of infection for Erwinia amylovora, the causal agent of fire blight of rosaceous plants. Before entering the tissue, the pathogen colonizes the stigmatic surface and has to compete for space and nutrient resources within the epiphytic community. Several epiphytes are capable of synthesizing antibiotics with which they antagonize phytopathogenic bacteria. Here, we report that a multidrug efflux transporter, designated NorM, of E. amylovora confers tolerance to the toxin(s) produced by epiphytic bacteria cocolonizing plant blossoms. According to sequence comparisons, the single-component efflux pump NorM is a member of the multidrug and toxic compound extrusion protein family. The corresponding gene is widely distributed among E. amylovora strains and related plant-associated bacteria. NorM mediated resistance to the hydrophobic cationic compounds norfloxacin, ethidium bromide, and berberine. A norM mutant was constructed and exhibited full virulence on apple rootstock MM 106. However, it was susceptible to antibiotics produced by epiphytes isolated from apple and quince blossoms. The epiphytes were identified as Pantoea agglomerans by 16S rRNA analysis and were isolated from one-third of all trees examined. The promoter activity of norM was twofold greater at 18°C than at 28°C. The lower temperature seems to be beneficial for host infection because of the availability of moisture necessary for movement of the pathogen to the infection sites. Thus, E. amylovora might employ NorM for successful competition with other epiphytic microbes to reach high population densities, particularly at a lower temperature.

A Helicobacter pylori TolC Efflux Pump Confers Resistance to Metronidazole

“…Similarly, expression of Burkholderia vietnamiensis NorM in an E. coli acrAB mutant strain complemented its hypersensitivity to norfloxacin (11). Thus, H. pylori HP1184 encodes a NorM homolog that actively extrudes ethidium bromide in vitro, similar to the homolog found in other bacteria (7,11,20). However, the H. pylori HP1184-knockout mutant was not more susceptible to norfloxacin, indicating a difference in substrate specificity.…”

“…Transformation of a hypersensitive E. coli strain with V. parahaemolyticus norM conferred resistance to norfloxacin and ethidium bromide, and elevated efflux of ethidium bromide was observed (20). In Erwinia amylovora NorM mediates resistance to hydrophobic cationic compounds like norfloxacin and ethidium bromide (7). Similarly, expression of Burkholderia vietnamiensis NorM in an E. coli acrAB mutant strain complemented its hypersensitivity to norfloxacin (11).…”

Colonization Patterns of an mCherry-Tagged Pectobacterium carotovorum subsp. brasiliense Strain in Potato Plants

“…sepedonicus, which forms bacterial aggregates embedded in an exopolymetric matrix and attaches to the walls of xylem vessels of potato plants (7,28). Colonization of the xylem vessels is also central in the systemic spread of gram-negative phytopathogens such as Erwinia amylovora (4,26). Furthermore, D. solani, a member of the SRE, has also been shown to utilize xylem vessels to systemically colonize potato plant tissues following root, stem, and leaf infection.…”

“…brasiliense 1692 and P. carotovorum subsp. brasiliense mCherry strains were prepared in LB broth and grown to a cell density of an optical density at 600 nm (OD 600 ) = 1 (≈1 × 10 8 CFU/ml), washed, and resuspended in 10 mM MgSO 4 .…”

Role of the Tet38 Efflux Pump in Staphylococcus aureus Internalization and Survival in Epithelial Cells

“…Many multidrug efflux pumps in Gram-negative bacteria like E. coli, K. pneumoniae, and E. cloacae are controlled by special regulatory systems that mediate responses to hostile environments (37). In addition, studies of Gram-negative efflux pumps revealed that the expression of several transporters of the RND (resistance-nodulation-division) family of multidrug (MDR) transporters were induced by and transported cellular metabolites as part of the bacterial cell physiology (38)(39)(40). Since Tet38 conferred resistance to fatty acids, a natural host defense component, we observed the effects of certain lipids on the gene expression levels of tet38 and its regulators tetR21 and mgrA.…”