Viral and parasitic cell ratios per free-living microbe across ecosystems

ABSTRACTIt is generally assumed that viruses outnumber cells on Earth by at least tenfold1–4. Virus-to-microbe ratios (VMR) are largely based on fluorescently-labelled viral-like particles (VLPs) counts. However, these exclude cell-infecting lytic and lysogenic viruses and potentially include many false positives, e.g. DNA-containing membrane vesicles, genetransfer agents or inert particles. Here, we develop a metagenome-based VMR estimate (mVRM) accounting for all viral stages (virion-lytic-lysogenic) using normalised counts of viral DNA-polymerases and cellular universal single-copy genes as proxies for individuals. To properly estimate mVMR in aquatic ecosystems, we generated metagenomes from co-occurring cellular and viral fractions (>50 kDa-200 μm size range) in freshwater, seawater and 6-14-32% salt solar-saltern ponds. Viruses outnumbered cells in non-blooming freshwater and marine plankton by around twofold. However, mVMR in 133 uniformly-analysed metagenomes from diverse ecosystems showed that free-living cells largely exceeded viruses and epibiont DPANN archaea and/or CPR bacteria in compact environments (sediments, soils, microbial mats, host-associated microbiomes). Along the Piggyback-the-winner model5 lines, lysogenic genes significantly correlated with cell, but not necessarily biotope, density. While viruses likely are the most diverse biological entities on Earth6,7, our results suggest that cells are the most abundant and that cellular parasites may exert population-size control in some high-density ecosystems.

Leishmania major Telomerase TERT Protein Has a Nuclear/Mitochondrial Eclipsed Distribution That Is Affected by Oxidative Stress

In its canonical role the reverse transcriptase telomerase recovers the telomeric repeats that are lost during DNA replication. Other locations and activities have been recently described for the telomerase protein subunit TERT in mammalian cells. In the present work, using biochemistry, molecular biology, and electron microscopy techniques, we found that in the human parasiteLeishmania major, TERT (and telomerase activity) shared locations between the nuclear, mitochondrial, and cytoplasmic compartments. Also, some telomerase activity and TERT protein could be found in ∼100-nm nanovesicles. In the mitochondrial compartment, TERT appears to be mainly associated with the kinetoplast DNA. WhenLeishmaniacells were exposed to H2O2, TERT changed its relative abundance and activity between the nuclear and mitochondrial compartments, with the majority of activity residing in the mitochondrion. Finally, overexpression of TERT inLeishmaniatransfected cells not only increased the parasitic cell growth rate but also increased their resistance to oxidative stress.

A Parasitic Phase-Specific Adhesin of Coccidioides immitis Contributes to the Virulence of This Respiratory Fungal Pathogen

ABSTRACT We report the isolation of a Coccidioides immitis gene (SOWgp) which encodes an immunodominant, spherule outer wall glycoprotein that is presented as a component of a parasitic phase-specific, membranous layer at the cell surface. The open reading frame of the gene from C. immitis isolate C735 translates a 422-amino-acid (aa) polypeptide that contains 6 copies of a 41- to 47-residue tandem repeat enriched in proline (20.4 mol%) and aspartate (19.7%). Two additional isolates of C. immitis produce SOWgps of different molecular sizes (328 and 375 aa) and show a corresponding difference in the number of tandem repeats (four and five, respectively). The accurate molecular sizes of these proline-rich antigens, as determined by surface-enhanced laser desorption/ionization mass spectrometry, are comparable to the predicted sizes from the translated protein sequences rather than the estimated sizes based on gel-electrophoretic separation. The results of Northern hybridization confirmed that SOWgp expression is parasitic phase specific, and immunoblot studies showed that elevated levels of production of this antigen occurred during early spherule development. The recombinant polypeptide (rSOWp) was shown to bind to mammalian extracellular matrix (ECM) proteins in an in vitro assay (laminin > fibronectin > collagen type IV), suggesting that the parasitic cell surface antigen may function as an adhesin. Deletion of the SOWgp gene by using a targeted gene replacement strategy resulted in partial loss of the ability of intact spherules to bind to ECM proteins and a significant reduction in virulence of the mutant strain. The wild-type gene was restored in the mutant by homologous recombination, and the revertant strain was shown to be as virulent as the parental isolate in our murine model of coccidioidomycosis. The parasitic cell surface glycoprotein encoded by the SOWgp gene appears to function as an adhesin and contributes to the virulence of C. immitis.

Cloning and Expression of the Gene Which Encodes a Tube Precipitin Antigen and Wall-Associated β-Glucosidase ofCoccidioides immitis

ABSTRACT We report the structure and expression of the Coccidioides immitis BGL2 gene which encodes a previously characterized 120-kDa glycoprotein of this fungal respiratory pathogen. The glycoprotein is recognized by immunoglobulin M tube precipitin (TP) antibody present in sera of patients with coccidioidomycosis, a reaction which has been used for serodiagnosis of early coccidioidal infection. The deduced amino acid sequence of BGL2 shows 12 potential N glycosylation sites and numerous serine-threonine-rich regions which could function as sites for O glycosylation. In addition, the protein sequence includes a domain which is characteristic of family 3 glycosyl hydrolases. Earlier biochemical studies of the purified 120-kDa TP antigen revealed that it functions as a β-glucosidase (EC 3.2.1.21 ). Its amino acid sequence shows high homology to several other reported fungal β-glucosidases which are members of the family 3 glycosyl hydrolases. Results of previous studies have also suggested that the 120-kDa β-glucosidase participates in wall modification during differentiation of the parasitic cells (spherules) ofC. immitis. In this study we showed that expression of the BGL2 gene is elevated during isotropic growth of spherules and the peak of wall-associated BGL2 enzyme activity correlates with this same phase of parasitic cell differentiation. These data support our hypothesis that the 120-kDa β-glucosidase plays a morphogenetic role in the parasitic cycle of C. immitis.