Barthelonids represent a deep-branching Metamonad clade with mitochondrion-related organelles generating no ATP

Abstract

23Running head: Phylogeny and putative MRO functions in a new metamonad clade. 25Abstract 28 We here report the phylogenetic position of barthelonids, small anaerobic flagellates 29 previously examined using light microscopy alone. Barthelona spp. were isolated from 30 geographically distinct regions and we established five laboratory strains. Transcriptomic data 31 generated from one Barthelona strain (PAP020) was used for large-scale, multi-gene 32 phylogenetic (phylogenomic) analyses. Our analyses robustly placed strain PAP020 at the 33 base of the Fornicata clade, indicating that barthelonids represent a deep-branching 34 Metamonad clade. Considering the anaerobic/microaerophilic nature of barthelonids and 35 preliminary electron microscopy observations on strain PAP020, we suspected that 36 barthelonids possess functionally and structurally reduced mitochondria (i.e. mitochondrion-37 related organelles or MROs). The metabolic pathways localized in the MRO of strain PAP020 38 were predicted based on its transcriptomic data and compared with those in the MROs of 39 fornicates. Strain PAP020 is most likely incapable of generating ATP in the MRO, as no 40 mitochondrial/MRO enzymes involved in substrate-level phosphorylation were detected. 41 Instead, we detected the putative cytosolic ATP-generating enzyme (acetyl-CoA synthetase), 42 suggesting that strain PAP020 depends on ATP generated in the cytosol. We propose two 43 separate losses of substrate-level phosphorylation from the MRO in the clade containing 44 barthelonids and (other) fornicates.45 46

Anaeramoebae are a divergent lineage of eukaryotes that shed light on the transition from anaerobic mitochondria to hydrogenosomes

“…caviae, 64 and Barthelona sp. 7 For each of the 155 proteins, we used the Arabidopsis thaliana or Homo sapiens homolog as a query against the predicted proteins of each Anaeramoeba species (e-value cut-off = 10e-10) using BLASTP 43 and retained up to five hits. Those potential homologs were then used as queries for a reciprocal BLAST search against a dataset containing the initial set of identified orthologs, but also their known deep paralogs (i.e., corresponding to duplications predating the last eukaryotic common ancestor, such as EF1-L and EF1-a).…”

Barthelonids represent a deep-branching metamonad clade with mitochondrion-related organelles predicted to generate no ATP

“…The assembled transcriptomes of strain PAP020 and phylogenetic alignments analysed in this study are available from the Dryad Digital Repository: https://doi.org/10.5061/dryad. 3tx95x6bn [57].…”

Reduced Mitochondria Provide an Essential Function for the Cytosolic Methionine Cycle

“…Leger et al 4 predicted GCS and SHMT in the MROs of all free-living fornicates and noted that glycine degradation correlates with their free-living lifestyle for an unclear reason. Moreover, GCS and SHMT were predicted to be localized in the MRO of other free-living Metamonada, such as Barthelona sp., Anaeramoeba flamelloides, and A. Ignava 29,76 and a number of other free-living, but also endobiotic, anaerobic or microaerophilic protists from the lineages of Archamoebae, breviates, heteroloboseans, ciliates, gregarines, Brevimastigomonas motovehiculus, and Blastocystis sp. [77][78][79][80][81][82][83][84][85][86] Our data provide a potential reason for maintaining GCS and SHMT in these organelles, namely the production of 1C-charged folate species to supply cytosolic 1C metabolism, and particularly the reaction in the methionine cycle catalyzed by methionine synthase.…”