Antibiotic- and metal-resistant endophytes inhabit Armeria maritima hyperaccumulator

Abstract

Background and aims: Recent research has recognized the presence of metal-resistant bacteria in plants and their role in phytoremediation intensification. However, information on the antibiotic resistance profile of those bacteria remains scarce. This study, describes the first isolation of endophytic bacteria from green parts of Armeria maritima growing on mine-tailing soil in southern Poland, and presents the resistance profile of these microorganisms. Methods: Bacteria were isolated from internal tissues of Armeria maritima and characterized. Minimal Inhibitory Concentration (MIC) of metals was determined by the plate dilution method using (CH3COO)2Pb and ZnSO4 supplemented medium; antibiotic susceptibility was determined by disk diffusion method according to EUCAST version 11.0; the whole genome sequencing was performed using the MiSeq platform (Illumina). The physicochemical properties of soil were evaluated according to European Standards. Results: Toxic metal-resistant bacteria were isolated from the green parts of Armeria maritima. The endophytes were identified as Pseudomonas spp. The annotated bacterial genomes carried genes encoding numerous metal ion transporters, metal reducing enzymes and efflux pump components. The bacteria were resistant to streptomycin, fosfomycin and ß-lactams. Moreover, genome analysis revealed the presence of MacAB-TolC efflux pump genes conferring resistance to macrolides, the multidrug efflux pumps AcrAB-TolC and MexAB-OprM. Conclusion: Armeria maritima is inhabited by endophytic bacteria identified as Pseudomonas species that are resistant to metals and to antibiotics. Under the One Health concept the contamination of soil and plants with ARB and ARGs should be monitored and limited and a regulatory framework for safety use of bacterial bioinoculants should be established.