Borrelia burgdorferi undergoes an infectious cycle that requires adaptation to different hosts and markeddifferences in environment. B. burgdorferi copes with its different environments by regulating the expression ofproteins required for survival in specific settings. The B. burgdorferi oligopeptide permease (Opp) is one of onlya few transporters encoded by the B. burgdorferi genome. Opp proteins in other bacteria serve multipleenvironmental adaptation functions. B. burgdorferi appears to broaden the usage of this transporter by utilizingfive different substrate binding proteins (OppA proteins) that interact with the integral membrane componentsof the transporter. Expression of the OppA proteins is individually regulated and may play different roles inadaptation to host environments. Very little is known about the mechanisms used by B. burgdorferi to regulatethe expression of different OppA proteins. Here we show that the alternative sigma factors, RpoS and RpoN,regulate the expression of oppA5 but not that of other oppA genes. Using a reporter assay with Escherichia coliand gel shift binding assays, we also show that the B. burgdorferi BosR/Fur homologue interacts with the oppA4promoter and that another candidate transcription factor, EbfC, interacts with the oppA5 promoter. Bindingto the promoters was confirmed by gel shift assays. Expression of BosR/Fur in its different hosts does appearto parallel the expression of oppA4. A better understanding of the factors involved in gene regulation in B.burgdorferi will help to identify coregulated proteins that may cooperate to allow the organism to survive in aspecific environment.A