Trichomonas vaginalis and Mycoplasma hominis: new tales of two old friends.

Trichomonas vaginalis is an anaerobic protist, responsible for the most prevalent non-viral sexually transmitted infection in humans. One of the most intriguing aspects of T. vaginalis pathobiology is the complex relationship with intracellular microbial symbionts: a group of dsRNA viruses belonging to family of Totiviridae (T. vaginalis virus), and eubacteria belonging to the Mycoplasma genus, in particular Mycoplasma hominis. Both microorganisms seem to strongly influence the lifestyle of T. vaginalis, suggesting a role of the symbiosis in the high variability of clinical presentation and sequelae during trichomoniasis. In the last few years many aspects of this unique symbiotic relationship have been investigated: M. hominis resides and replicates in the protozoan cell, and T. vaginalis is able to pass the bacterial infection to both mycoplasma-free protozoan isolates and human epithelial cells; M. hominis synergistically upregulates the proinflammatory response of human monocytes to T. vaginalis. Furthermore, the influence of M. hominis over T. vaginalis metabolism and physiology has been characterized. The identification of a novel species belonging to the class of Mollicutes (Candidatus Mycoplasma girerdii) exclusively associated to T. vaginalis opens new perspectives in the research of the complex series of events taking place in the multifaceted world of the vaginal microbiota, both under normal and pathological conditions.

Physiological traits of endornavirus-infected and endornavirus-free common bean (Phaseolus vulgaris) cv Black Turtle Soup.

This study evaluated the physiological traits of eight lines of common bean (Phaseolus vulgaris) cv. Black Turtle Soup, four of which were double-infected with Phaseolus vulgaris endornavirus 1 and Phaseolus vulgaris endornavirus 2, and four of which were endornavirus-free. Plants from all eight lines were morphologically similar and did not show statistically significant differences in plant height, wet weight, number of days to flowering and pod formation, pods per plant, pod thickness, seed size, number of seeds per pod, and anthocyanin content. However, the endornavirus-infected lines had faster seed germination, longer radicle, lower chlorophyll content, higher carotene content, longer pods, and higher weight of 100 seeds, all of which were statistically significant. The endornaviruses were not associated with visible pathogenic effects.

New insights about ORF1 coding regions support the proposition of a new genus comprising arthropod viruses in the family Totiviridae.

Analyzing the positions of 2A-like polypeptide cleavage sites in all available genomes of arthropod totiviruses we propose the limits of all ORF1 coding sequences and observed that two proteins previously predicted in infectious myonecrosis virus genome are unique in the arthropod totiviruses group. A putative protein cleavage site upstream the major capsid protein was also identified only in these genomes. In addition, protein models generated using ab initio and threading approaches revealed conserved structures possibly related to formation of viral protrusions and RNA packaging, clarifying the mechanisms involved in the extracellular transmission. These data appoints that the group formed by arthropod totiviruses are sufficient distinctive to be clustered in new genus belonging to the Totiviridae family, in agreement with previous phylogenetic analysis.

Kinetics of ribosomal pausing during programmed -1 translational frameshifting.

In the Saccharomyces cerevisiae double-stranded RNA virus, programmed -1 ribosomal frameshifting is responsible for translation of the second open reading frame of the essential viral RNA. A typical slippery site and downstream pseudoknot are necessary for this frameshifting event, and previous work has demonstrated that ribosomes pause over the slippery site. The translational intermediate associated with a ribosome paused at this position is detected, and, using in vitro translation and quantitative heelprinting, the rates of synthesis, the ribosomal pause time, the proportion of ribosomes paused at the slippery site, and the fraction of paused ribosomes that frameshift are estimated. About 10% of ribosomes pause at the slippery site in vitro, and some 60% of these continue in the -1 frame. Ribosomes that continue in the -1 frame pause about 10 times longer than it takes to complete a peptide bond in vitro. Altering the rate of translational initiation alters the rate of frameshifting in vivo. Our in vitro and in vivo experiments can best be interpreted to mean that there are three methods by which ribosomes pass the frameshift site, only one of which results in frameshifting.

Site-specific binding of polymerase-containing particles of the Giardia lamblia double-stranded RNA virus to the viral plus-strand RNA.

The non-segmented, double-stranded RNA genome of the Giardia lamblia virus (GLV) contains two genes encoding the major capsid protein (gag) and a fusion of gag with the viral RNA-dependent RNA polymerase (pol). Computer analysis of the viral RNA genome revealed three putative stem-loop structures that were predicted to mediate replication, transcription and packaging of the GLV genomic RNA by binding to the pol domain of the virus-encoded fusion protein. To provide evidence of these postulated RNA/protein interactions, gel retardation assays were employed to examine the potential binding capacity of various viral RNA genome-related sequences to native GLV protein(s). Viral proteins were obtained by disrupting purified GLV particles under low-ionic-strength conditions. The resulting viral protein particles maintained their RNA polymerase activity in the presence of GLV genomic RNA and thus appeared to be suitable tools for the analyses of GLV-protein-mediated binding reactions. A 72-nt short single-stranded in vitro transcript containing a putative stem-loop structure predicted to participate in the packaging of GLV (+)-strand RNA bound specifically to the disrupted virus particles. RNAs containing modified motifs of this stem-loop structure failed to bind to the GLV capsid.