<italic>Borrelia burgdorferi</italic> genes, <italic>bb0639</italic>‐<italic>0642</italic>, encode a putative putrescine/spermidine transport system, PotABCD, that is spermidine specific and essential for cell survival.

Summary: Polyamines are an essential class of metabolites found throughout all kingdoms in life. <italic>Borrelia burgdorferi</italic> harbors no enzymes to synthesize or degrade polyamines yet does contain a polyamine uptake system, <italic>potABCD</italic>. In this report, we describe the initial characterization of this putative transport system. After several unsuccessful attempts to inactivate <italic>potABCD</italic>, we placed the operon under the control of an inducible LacI promoter expression system. Analyses of this construct confirmed that <italic>potABCD</italic> was required for <italic>in vitro</italic> survival. Additionally, we demonstrated that the <italic>potABCD</italic> operon were upregulated <italic>in vitro</italic> by low osmolarity. Previously, we had shown that low osmolarity triggers the activation of the Rrp2/RpoN/RpoS regulatory cascade, which regulates genes essential for the transmission of spirochetes from ticks to mammalian hosts. Interestingly, induction of the <italic>pot</italic> operon was only affected in an <italic>rpoS</italic> mutant but not in a <italic>rpoN</italic> mutant, suggesting that the genes were RpoS dependent and RpoN independent. Furthermore, <italic>potABCD</italic> was upregulated during tick feeding concomitant with the initiation of spirochete replication. Finally, uptake experiments determined the specificity of <italic>B. burgdorferi</italic>'s PotABCD for spermidine. [ABSTRACT FROM AUTHOR]