Nucleotide Parasitism by Simkania negevensis ( Chlamydiae )

Abstract

ABSTRACT Intracellular bacteria live in an environment rich in most essential metabolites but need special mechanisms to access these substrates. Nucleotide transport proteins (NTTs) catalyze the import of ATP and other nucleotides from the eukaryotic host into the bacterial cell and render de novo synthesis of these compounds dispensable. The draft genome sequence of Simkania negevensis strain Z, a chlamydial organism considered a newly emerging pathogen, revealed four genes encoding putative nucleotide transport proteins ( Sn NTT1 to Sn NTT4), all of which are transcribed during growth of S. negevensis in Acanthamoeba host cells, as confirmed by reverse transcription-PCR. Using heterologous expression in Escherichia coli , we could show that Sn NTT1 functions as an ATP/ADP antiporter, Sn NTT2 as a guanine nucleotide/ATP/H + symporter driven by the membrane potential, and Sn NTT3 as a nucleotide triphosphate antiporter. In addition, Sn NTT3 is able to transport dCTP, which has not been shown for a prokaryotic transport protein before. No substrate could be identified for Sn NTT4. Taking these data together, S. negevensis employs a set of nucleotide transport proteins to efficiently tap its host's energy and nucleotide pools. Although similar to other chlamydiae, these transporters show distinct and unique adaptations with respect to substrate specificities and mode of transport.