Evolution of Fe/S cluster biogenesis in the anaerobic parasite Blastocystis

Abstract

Iron/sulfur cluster (ISC)-containing proteins are essential components of cells. In most eukaryotes, Fe/S clusters are synthesized by the mitochondrial ISC machinery, the cytosolic iron/sulfur assembly system, and, in photosynthetic species, a plastid sulfurmobilization (SUF) system. Here we show that the anaerobic human protozoan parasite Blastocystis, in addition to possessing ISC and iron/sulfur assembly systems, expresses a fused version of the SufC and SufB proteins of prokaryotes that it has acquired by lateral transfer from an archaeon related to the Methanomicrobiales, an important lineage represented in the human gastrointestinal tract microbiome. Although components of the Blastocystis ISC system function within its anaerobic mitochondrion-related organelles and can functionally replace homologues in Trypanosoma brucei, its SufCB protein has similar biochemical properties to its prokaryotic homologues, functions within the parasite's cytosol, and is up-regulated under oxygen stress. Blastocystis is unique among eukaryotic pathogens in having adapted to its parasitic lifestyle by acquiring a SUF system from nonpathogenic Archaea to synthesize Fe/S clusters under oxygen stress.iron/sulfur cluster biosynthesis | lateral gene transfer | parasite evolution | sulfur-mobilization machinery | oxygen stress adaptation

Evolution of the Cytosolic Iron-Sulfur Cluster Assembly Machinery in Blastocystis Species and Other Microbial Eukaryotes

“…This work, along with a previous study (17), demonstrated that key components of the ISC and CIA systems are encoded by genes in the Blastocystis sp. NandII genome and that they localize in this organism's MROs and cytosol, respectively.…”

“…In a previous study, we showed that three different Fe/S cluster biosynthetic machineries were likely present in the anaerobic parasite Blastocystis (17). We localized and functionally characterized the mitochondrial Fe/S cluster (ISC) machinery and the cytosolic SUF machinery, but only limited data regarding the presence of the CIA machinery were available.…”

“…For the immunolocalization experiments using transmission electron microscopy, Blastocystis NandII cells were fixed and manipulated using the protocols described previously (17). The prepared grids were incubated in sodium borohydride (1 mg/ml) for 10 min, followed by a 10-min incubation in glycine buffer (30 mM glycine in 0.1 M borate buffer, pH 9.6).…”

“…Blastocystis cells were pelleted at 800 ϫ g for 10 min and then washed twice in 1ϫ Locke's solution before being suspended in 0.15 M NaCl. Cells were disrupted using ultrasonication (for 30 s at 30-s intervals, 6 cycles) (17,19) on ice. Following disruption, protease inhibitor cocktail (10 l; Sigma) was added to the sample, and the mixture was then centrifuged at 10,000 ϫ g for 10 min at 4°C.…”

“…Instead, their ge-nomes encode NIF system components that were acquired by lateral gene transfer (LGT) from epsilonproteobacteria and that localize both in the cytosol and in their organelles (14)(15)(16). Another example is found in Blastocystis, an obligate anaerobic parasite that encodes a functional fused version of the SufC and SufB proteins, SufCB, that was also acquired by LGT, in this case, from a methanoarchaeal lineage, and that functions in the cytosol of the organism (17). The presence of both this SUF protein and components of the CIA Fe/S cluster biosynthetic pathway in Blastocystis (18) raises questions regarding their respective cytosolic roles.…”