Abstract
Recent research has suggested that polyamines (putrescine, spermidine, and spermine) in the intestinal tract impact the health of animals either negatively or positively. The concentration of polyamines in the intestinal tract results from the balance of uptake and export of the intestinal bacteria. However, the mechanism of polyamine export from bacterial cells to the intestinal lumen is still unclear. In Escherichia coli, PotE was previously identified as a transporter responsible for putrescine excretion in an acidic growth environment. We observed putrescine concentration in the culture supernatant was increased from 0 to 50 μm during growth of E. coli under neutral conditions. Screening for the unidentified putrescine exporter was performed using a gene knock-out collection of E. coli, and deletion of sapBCDF significantly decreased putrescine levels in the culture supernatant. Complementation of the deletion mutant with the sapBCDF genes restored putrescine levels in the culture supernatant. Additionally, the ΔsapBCDF strain did not facilitate uptake of putrescine from the culture supernatant. Quantification of stable isotope-labeled putrescine derived from stable isotope-labeled arginine supplemented in the medium revealed that SapBCDF exported putrescine from E. coli cells to the culture supernatant. It was previously reported that SapABCDF of Salmonella enterica sv. typhimurium and Haemophilus influenzae conferred resistance toantimicrobial peptides; however, the E. coli ΔsapBCDF strain did not affect resistance to antimicrobial peptide LL-37. These results strongly suggest that the natural function of the SapBCDF proteins is the export of putrescine.
Highlights
Recent research has suggested that polyamines in the intestinal tract impact the health of animals either negatively or positively
We previously reported that polyamines in the intestinal tract are derived from the gut microbiota [7], and it has been recently reported that polyamines in the intestinal tract impact the health of animals either negatively (8 –10) or positively [11,12,13]
The screening indicated that the putrescine concentration of the culture supernatant of E. coli ⌬sapF strain (JW1283) was the lowest (18.6 M) of the tested strains, and the second lowest putrescine concentration of the culture supernatant was 25.5 M observed in ⌬sapD strain (JW1284)
Summary
Recent research has suggested that polyamines (putrescine, spermidine, and spermine) in the intestinal tract impact the health of animals either negatively or positively. In Escherichia coli, PotE was previously identified as a transporter responsible for putrescine excretion in an acidic growth environment. Quantification of stable isotope-labeled putrescine derived from stable isotope-labeled arginine supplemented in the medium revealed that SapBCDF exported putrescine from E. coli cells to the culture supernatant. Typhimurium and Haemophilus influenzae conferred resistance to antimicrobial peptides; the E. coli ⌬sapBCDF strain did not affect resistance to antimicrobial peptide LL-37 These results strongly suggest that the natural function of the SapBCDF proteins is the export of putrescine. SpeF converts ornithine to putrescine with consumption of a proton, and PotE exports putrescine with uptake of ornithine [18]. Through this process, E. coli adapts to the acidic environment. We performed a genome-wide screening for novel putrescine exporters of E. coli and demonstrated biochemically that the sapBCDF operon contributes to putrescine export from the cell to the environment
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