Ultrastructural, Cytochemical, and Comparative Genomic Evidence of Peroxisomes in Three Genera of Pathogenic Free-Living Amoebae, Including the First Morphological Data for the Presence of This Organelle in Heteroloboseans

Abstract

<jats:title>Abstract</jats:title> <jats:p>Peroxisomes perform various metabolic processes that are primarily related to the elimination of reactive oxygen species and oxidative lipid metabolism. These organelles are present in all major eukaryotic lineages, nevertheless, information regarding the presence of peroxisomes in opportunistic parasitic protozoa is scarce and in many cases it is still unknown whether these organisms have peroxisomes at all. Here, we performed ultrastructural, cytochemical and bioinformatic studies to investigate the presence of peroxisomes in three genera of free-living amoebae from two different taxonomic groups that are known to cause fatal infections in humans. By transmission electron microscopy, round structures with a granular content limited by a single membrane were observed in Acanthamoeba castellanii, Acanthamoeba griffini, Acanthamoeba polyphaga, Acanthamoeba royreba, Balamuthia mandrillaris (Amoebozoa) and Naegleria fowleri (Heterolobosea). Further confirmation for the presence of peroxisomes was obtained by treating trophozoites in situ with diaminobenzidine and hydrogen peroxide, which showed positive reaction products for the presence of catalase. We then performed comparative genomic analyses to identify predicted peroxin homologues in these organisms. Our results demonstrate that a complete set of peroxins -which are essential for peroxisome biogenesis, proliferation and protein import- are present in all of these amoebae. Likewise, our in silico analyses allowed us to identify a complete set of peroxins in Naegleria lovaniensis and three novel peroxin homologues in Naegleria gruberi. Thus, our results indicate that peroxisomes are present in these three genera of free-living amoebae and that they have a similar peroxin complement despite belonging to different evolutionary lineages.</jats:p>

Giardia intestinalis and its endomembrane system*

“…Certainly, future studies are necessary to show this organelle's participation in the protozoan metabolism. Recent studies have shown the presence of peroxisomes in the anaerobic protists Manstigamoeba balamuthi (Le et al, 2020) and Acanthamoeba , Balamuthis , and Naegleria (Gonzáles‐Robles et al, 2020).…”

Acanthamoeba castellanii exhibits intron retention during encystment

“…in several species of Acanthamoeba and other free-living amoebae and are also involved in protein import, which could be affected during encystment (González-Robles et al 2020).…”

Application of the omics sciences to the study of Naegleria fowleri, Acanthamoeba spp., and Balamuthia mandrillaris: current status and future projections

“…Another comparative genomics approach was performed between FLAs to identify the presence of peroxin orthologs, thus confirming the presence of peroxisomes in A. castellanii , A. griffini , A. polyphaga , A. royreba , and other amoebas such as B. mandrillaris , N. fowleri , and N. lovaniensis . This information that was very scarce in the field of research in opportunistic FLAs [ 28 ]. The importance of these organelles is related to their crucial role in various anabolic and catabolic pathways, changing their function depending on the organism that owns them [ 3 ].…”