PstSCAB and SapBCDF are putrescine exporters in Proteus mirabilis

Proteus mirabilis is a cause of urinary tract infection. Putrescine, an aliphatic amine, acts as a messenger molecule during P. mirabilis urothelial invasion. Inhibition of putrescine-mediated cell-cell communication in P. mirabilis may be an effective method for control of urinary tract infection. PlaP is a primary putrescine importer in P. mirabilis PM7002. However, no putrescine exporters have been identified to date. In this study, we screened the putrescine exporter gene from P. mirabilis PM7002 transposon mutant library using a previously developed high-throughput putrescine quantification method and revealed that PstSCAB is a novel putrescine exporter. SapBCDF and PotE have been reported as a putrescine exporter and putrescine-ornithine antiporter, respectively, in Escherichia coli. Although P. mirabilis possesses the SapBCDF and PotE homologs, the effects of these homologs on the putrescine export are unclear. We investigated the contributions of SapBCDF and PotE homologs on putrescine export in P. mirabilis using gene deletion and found that SapBCDF is a putrescine exporter. P. mirabilis exhibits unique and highly coordinated multicellular migration called swarming. Putrescine mediates cell-cell communication during swarming. Therefore, we evaluated the effects of PstSCAB and SapBCDF on swarming. As a result, the swarming diameters of P. mirabilis ΔpstSCAB and ΔsapBCDF were significantly lower than that of the wild type. This revealed that PstSCAB and SapBCDF are putrescine exporters that mediate cell-cell communication during swarming. Inhibition of PstSCAB and SapBCDF is a possible target for treating P. mirabilis-related urinary tract infection.

Antibiotics are the primary treatment for bacterial urinary tract infections (UTIs). However, overuse of antibiotics promotes the emergence of antibiotic-resistant bacteria; therefore, it is desirable to develop drugs that specifically inhibit virulence without promoting the emergence of antibiotic resistance. Proteus mirabilis causes UTI and uniquely uses putrescine for cell-cell communication during urinary tract invasion. Inhibition of putrescine-mediated cell-cell communication in P. mirabilis impairs its invasion of urothelial cells. Therefore, proteins responsible for putrescine-mediated cell-cell communication are a potential target for treating P. mirabilis UTIs. However, the putrescine exporter of P. mirabilis has yet to be identified. Here, we identified two putrescine exporters of P. mirabilis, PstSCAB and SapBCDF. Furthermore, P. mirabilis ΔpstSCAB and ΔsapBCDF strains showed a lack of swarming activity. This study indicates PstSCAB and SapBCDF as potential targets for treating UTIs caused by P. mirabilis.