Serratiochelins A and B from Serratia marcescensshow xenosiderophoric characteristics towards Acinetobacter baumanniiand Mycobacterium tuberculosis

Abstract

Purpose:To evaluate the xenosiderophoric properties of siderophores produced by Serratia marcescens towards Acinetobacter baumannii, Staphylococcus aureus and Mycobacterium tuberculosis. Methods:A non-pigmented strain of S. marcescens was isolated from soil after cultivation in ironlimited LB medium. The isolate was identified using both biochemical and 16S rDNA molecular phylogenetic analyses. The bacterial secondary metabolites were extracted after solid state fermentation in sterile rice medium. The extract was separated using chromatography, and the resulting compounds were analyzed by mass spectrometry and nuclear magnetic resonance spectroscopy. The iron-chelating, growth-promoting and cytotoxic activities of the compounds were determined using standard protocols. Results:Two siderophore compounds (serratiochelins A and B) were isolated from the fermentation extract of S. marcescens. Characteristic of siderophores, serratiochelins A and B exhibited varying degrees of iron-chelating activities. The compounds displayed xenosiderophoric properties by supporting the growth of A. baumannii and M. tuberculosis in iron-limited media. In addition, the siderophores displayed cytotoxic activity against human cells, with serratiochelin A showing the higher activity with IC50 of 3.20 and 6.26 µM against THP-1 and HEK-293 cells, respectively. Conclusion:This study demonstrates the isolation of serratiochelins A and B from a soil-derived nonpigmented strain of S. marcescens. The siderophores support the growth of A. baumannii and M. tuberculosis, and thus, have prospects for development as sideromycins against these multidrug resistant (MDR) organisms.