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

Abstract

cAll organisms require S-adenosylmethionine (SAM) as a methyl group donor and cofactor for various biologically important processes. However, certain obligate intracellular parasitic bacteria and also the amoeba symbiont Amoebophilus asiaticus have lost the capacity to synthesize this cofactor and hence rely on its uptake from host cells. Genome analyses revealed that A. asiaticus encodes a putative SAM transporter. The corresponding protein was functionally characterized in Escherichia coli: import studies demonstrated that it is specific for SAM and S-adenosylhomocysteine (SAH), the end product of methylation. SAM transport activity was shown to be highly dependent on the presence of a membrane potential, and by targeted analyses, we obtained direct evidence for a proton-driven SAM/SAH antiport mechanism. Sequence analyses suggest that SAM carriers from Rickettsiales might operate in a similar way, in contrast to chlamydial SAM transporters. SAM/SAH antiport is of high physiological importance, as it allows for compensation for the missing methylation cycle. The identification of a SAM transporter in A. asiaticus belonging to the Bacteroidetes phylum demonstrates that SAM transport is more widely spread than previously assumed and occurs in bacteria belonging to three different phyla (Proteobacteria, Chlamydiae, and Bacteroidetes).

WhollyRickettsia! Reconstructed Metabolic Profile of the Quintessential Bacterial Parasite of Eukaryotic Cells

“…Our observations are in line with the proposition that the acquisition of metabolite transport systems facilitates the degradation of apposite biosynthetic pathways in rickettsiae ( 13 ). Remarkably, the EamA transporters were found piggybacking on integrative conjugative elements that appear to seed Rickettsia genomes with genes associated with intracellular invasion and survival ( 60 ); lateral transfer of such elements has occurred with obligate intracellular members of the phylum Bacteroidetes ( 88 ).…”

“…SLC5sbd and SLC5sbd+HK (fusion protein with His kinase domain) transporters are not linked with specific metabolites because of their known broad range of substrates (e.g., sugars, amino acids, organo-cations such as choline, nucleosides, inositols, vitamins, urea, or anions). Asterisks indicate transporters previously shown to be associated with mobile genetic elements and/or predicted to be spread by lateral gene transfer across diverse intracellular bacteria ( 60 , 88 , 126 , 127 ). Transporter names and family identifications ( 123 ) are as follows: ABC, ATP-binding cassette (3.A.1); AAA, ATP:ADP antiporter (2.A.12); DMT, drug/metabolite transporter (2.A.7); VUT, vitamin uptake transporter (2.A.88); AEC (2.A.69); MFS, major facilitator superfamily (2.A.1); APC, amino acid polyamine organo-cation (2.A.3); DAACS, dicarboxylate/amino acid:cation (Na + or H + ) symporter (2.A.23); SSS, solute:sodium symporter (2.A.21).…”

Transcriptome Sequencing Reveals Novel Candidate Genes forCardinium hertigii-Caused Cytoplasmic Incompatibility and Host-Cell Interaction

“…Four moderately expressed putative nucleotide transport proteins were found in Cardinium : CAHE_0018, CAHE_0158, CAHE_0160, and CAHE_0789, all of which belong to the ATP:ADP antiporter family. c Eper1 also expresses a putative S -adenosylmethionine transporter (CAHE_0109, moderate expression), which shows 47% amino acid identity to the functionally characterized homolog from Amoebophilus asiaticus ( 40 ) and 93% amino acid identity to a homolog in c BtQ1 ( 29 ). The transport system Opp A-F (CAHE_0240 to _0242, _0244, and _0245) and the C 4 -dicarboxylate transporter DcuAB (CAHE_0645 and _0647) were moderately expressed, indicating a functional import system for oligopeptides, amino acids, and dicarboxylates.…”

Improved axenization method reveals complexity of symbiotic associations between bacteria and acanthamoebae

“…The role of the bacterial symbionts for the biology and ecology of acanthamoebae is, however, currently unknown. While many of them seem to tap their host's metabolism (Trentmann et al ., ; Haferkamp et al ., ), which is indicative for a parasitic lifestyle, a potential benefit for the host cannot be excluded and might explain their prevalence, even at small spatial scales.…”