Molecular characterization of a homolog of the ferric-uptake regulator, Fur, from the marine bacterium Marinobacter algicola DG893

A drug-free strategy to combat bacterial infections with magnetic nanoparticles biosynthesized in bacterial pathogens

The extensive and indiscriminate use of antibiotics in the ongoing COVID-19 pandemic might significantly contribute to the growing number of multiple drug resistant (MDR) bacteria. With the dwindling pipeline of new and effective antibiotics, we might soon end up in a post-antibiotic era, in which even common bacterial infections would be a challenge to control. To prevent this, an antibiotic-free strategy would be highly desirable. Magnetic nanoparticle (MNP)-mediated hyperthermia-induced antimicrobial therapy is an attractive option as it is considered safe for human use. Given that iron and zinc are critical for bacterial virulence, we evaluated the response of multiple pathogenic bacteria to these elements. Treatment with 1 mM iron and zinc precursors resulted in the intracellular biosynthesis of MNPs in multiple Gram-positive and Gram-negative disease-causing bacteria. The superparamagnetic nanoparticles in the treated bacteria/biofilms, generated heat upon exposure to an alternating magnetic field (AMF), which resulted in an increase in the temperature (5-6 °C) of the milieu with a subsequent decrease in bacterial viability. Furthermore, we observed for the first time that virulent bacteria derived from infected samples harbour MNPs, suggesting that the bacteria had biosynthesised the MNPs using the metal ions acquired from the host. AMF treatment of the bacterial isolates from the infected specimens resulted in a strong reduction in viability (3-4 logs) as compared to vancomycin/ciprofloxacin treatment. The therapeutic efficacy of the MNPs to induce bacterial death with AMF alone was confirmed ex vivo using infected tissues. Our proposed antibiotic-free approach for killing bacteria using intracellular MNPs is likely to evolve as a promising strategy to combat a wide range of bacterial infections.

The global regulatory effect of Edwardsiella tarda Fur on iron acquisition, stress resistance, and host infection: A proteomics-based interpretation

Ferric uptake regulator (Fur) is an important transcriptional regulator of Gram-negative bacteria. Edwardsiella tarda is a severe fish bacterial pathogen with a broad host range that includes humans. In this study, we examined the regulatory function of Fur in E. tarda via a proteomic approach. Compared to the wild type TX01, the fur mutant TX01Δfur exhibited (i) retarded growth, (ii) enhanced siderophore production, (iii) increased acid tolerance, which is in contrast to observations in other bacterial species, (iv) decreased survival against oxidative stress and host serum, (v) impaired ability to inhibit host immune response, (vi) attenuated tissue infectivity and overall virulence. The deficiency of TX01Δfur was rescued by introduction of an exogenous fur gene. iTRAQ-based comparative proteomic analysis of TX01Δfur and TX01 identified 89 differentially expressed proteins that cover a wide range of functional categories including those affected by fur mutation. In addition, 16 proteins were identified for the first time to be regulated by Fur in Gram-negative bacteria. These results provide the first protein-based interpretation of the global impact of Fur on the physiology and infectivity of E. tarda.

SIGNIFICANCE

This study demonstrates that in E. tarda, Fur controls multiple aspects of bacterial life, including growth, metabolism, iron acquisition, stress response, and host infection. In line with these observations, proteomics analysis identified a large amount of proteins affected in expression by Fur, which are involved in bacterial physiology and infectivity. Hence, these results link for the first time the pleiotropic effect of Fur with global protein expression and shed new light on the function and regulatory mechanism of Fur in pathogenic bacteria.