Nucleotide Parasitism by Simkania negevensis ( Chlamydiae )

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 (SnNTT1 to SnNTT4), 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 SnNTT1 functions as an ATP/ADP antiporter, SnNTT2 as a guanine nucleotide/ATP/H ؉ symporter driven by the membrane potential, and SnNTT3 as a nucleotide triphosphate antiporter. In addition, SnNTT3 is able to transport dCTP, which has not been shown for a prokaryotic transport protein before. No substrate could be identified for SnNTT4. 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.Nucleotide transport proteins (NTTs) are commonly linked to the term "energy parasitism" (55) because they enable obligate intracellular bacteria to harvest ATP and other highenergy compounds from eukaryotic host cells. Among bacteria, NTT proteins catalyzing ATP/ADP exchange have been found in Chlamydiae and Rickettsiales, comprising major intracellular pathogens of humans (15,45,48,62,64,67), and recently also in the obligate intracellular veterinary pathogen Lawsonsia intracellularis belonging to the Deltaproteobacteria (63), in the plant pathogen "Candidatus Liberibacter asiaticus" belonging to the Rhizobiales (75), and in the obligate intracellular amoeba symbiont "Candidatus Amoebophilus asiaticus" belonging to the Bacteroidetes (65). In addition to ATP/ADP translocases, some obligate intracellular bacteria encode nucleotide transport isoforms for the import of nucleotides other than ATP or the cofactor NAD ϩ (7,22,26,27), thereby compensating for their inability to synthesize these metabolites de novo (22,33,66,76). Nucleotide transporters are thus important proteins for host cell interaction of obligate intracellular bacteria. Interestingly, nucleotide transport proteins were also found in eukaryotes: in plant and algal plastids (5,48,54,68,79) and in the microsporidian parasite Encephalitozoon cuniculi (73).In Chlamydiae, ATP uptake activity was first described for the avian pathogen Chlamydophila psittaci (28). Nearly 2 decades later, two nucleotide transport proteins of the human pathogen Chlamydia trachomatis were identified on the molecular level; one transporter catalyzes ATP/ADP exchange, and the second transporter mediates net uptake of RN...

Simkania negevensis, an insight into the biology and clinical importance of a novel member of the Chlamydiales order

“…In S. negevensis, entry in the citrate cycle can occur: (a) through acetyl-CoA produced from pyruvate following glycolysis and (b) through the transformation of asparagine in fumarate (Collingro et al, 2011;Omsland et al, 2014). Moreover, Waddliaceae, Parachlamydiaceae and Simkaniaceae are able to synthetize NAD þ from nicotinamide (Bertelli et al, 2010;Omsland et al, 2014) and S. negevensis can, additionally, use asparagine as a source of NADþ (Collingro et al, 2011;Knab et al, 2011;Omsland et al, 2014). Finally, an in vitro experiment by Kahane et al suggests that S. negevensis is able to grow in a glucose free medium; indeed the number of infectious forming units was similar using a Roswell Park Memorial Institute (RPMI) media depleted in glucose and supplemented with 1% glucose .…”

“…Four isoforms of nucleotides transporters have been identified in S. negevensis: SnSTT1, an ADP/ATP antiporter; SnSTT2, a guanine/ATP/ H þ symporter; SnSTT3 a global nucleotide triphosphate antiporter, also able to transport deoxy-CTP (dCTP). The function of the last transporter, SnSTT4, is unknown (Knab et al, 2011). The ability to transport dCTP is unique among prokaryotes and might represent a selective metabolic advantage for S. negevensis, favoring its relative growth in environments rich in cytosine.…”

“…§ § (Collingro et al, 2011;Rusconi & Greub, 2013). jjjj (Bertelli et al, 2010;Carlson et al, 2006;Collingro et al, 2011;Horn et al, 2004;Knab et al, 2011;Omsland et al, 2014).…”

The Endosymbiont Amoebophilus asiaticus Encodes an S -Adenosylmethionine Carrier That Compensates for Its Missing Methylation Cycle

“…In these organisms, essential metabolic pathways are often truncated or missing completely, and hence, import of intermediates or products is of high physiological importance. In the past years, several carrier proteins that mediate the provision of diverse metabolically relevant molecules and thus compensate for the reduced biosynthetic activity in intracellular bacteria have been identified (15,16,(23)(24)(25)(26)(27)(28)(29)43). Analysis of the genome of A. asiaticus revealed that its size is comparable to those of other intracellular bacteria; however, it encodes an unusually small number of proteins involved in metabolic processes (32).…”

“…A reduced genome size accompanied by the loss of biosynthetic pathways and the recruitment of carriers for compensation for missing or truncated metabolic pathways is a characteristic common feature of Chlamydiales and Rickettsiales (21,22): specific nucleotide transporters were shown to allow energy parasitism and complementation of missing purine and pyrimidine nucleotide or cofactor biosynthesis pathways (23)(24)(25)(26)(27)(28)(29). Deciphering of more and more genomes demonstrated that many intracellular bacteria are biosynthetically highly impaired.…”