Exploring Iron Scavenging as an Under-Explored Mode for Pathogen Elimination by Bacillus-Based Probiotics
Abstract:
Iron is a vital nutrient for aerobic organisms, but its (bio-)availability is limited in the lower intestine, leading to competition among microbial species. To address this scarcity, microbes produce iron- scavenging compounds such as siderophores. Certain gut pathogens are more iron-dependent than beneficial gut microbes, and iron promotes their replication and virulence. Bacillus species have antimicrobial effects against these pathogens through the pro duction of secondary metabolites with direct inhibitory effects. The current study aimed to explore the less-studied effect of siderophores from a novel Bacillus licheniformis G3 in the fight against Salmonella. Earlier research has shown that the Bacillus licheniformis G3 reduced the prevalence of Salmonella in salmonellosis-infected broiler birds. The genomic mining of the Bacillus licheniformis G3 revealed the presence of several siderophore gene clusters. The in vitro iron binding capacity of the Bacilli was confirmed by chrome azurol S assay, while E. coli and Salmonella enterica demonstrated poor binding capacity. Further, the preferential iron binding capacity of the cell-free supernatant (CFS) of the Bacilli strain was tested by incubating it with Salmonella enterica in a medium spiked with ferric salt. Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) analysis of the spent media revealed decreased iron concentration in the group supplemented with CFS, indicating reduced iron availability for Salmonella growth, possibly due to iron chelation by the CFS. These findings suggest the positive role of siderophores in combating Salmonella's iron-dependent pathogenicity. Further exploration of Bacilli-based siderophores in regulating host iron homeostasis against other enteric pathogens may unveil their pivotal role in conferring an advantage over pathogens.
