The infectivity and host range of Orgyia anartoides nucleopolyhedrovirus

The painted apple moth (PAM), Teia anartoides (Walker) (Lepidoptera: Lymantriidae) made a recent incursion into New Zealand. A nucleopolyhedrovirus (NPV), Orgyia anartoides NPV (OranNPV), originally isolated from PAM in Australia, was tested for its pathogenicity to PAM and a range of non‐target insect species found in New Zealand, to evaluate its suitability as a microbial control for this insect invader. Dosage‐mortality tests showed that OranNPV was highly pathogenic to PAM larvae; mean LT₅₀ values for third instars ranged from 17.9 to 8.1 days for doses from 10² to 10⁵ polyhedral inclusion bodies/larva, respectively. The cause of death in infected insects was confirmed as OranNPV. Molecular analysis established that OranNPV can be identified by PCR and restriction digestion, and this process complemented microscopic examination of infected larvae. No lymantriid species occur in New Zealand; however, the virus had no significant effects on species from five other lepidopteran families (Noctuidae, Tortricidae, Geometridae, Nymphalidae and Plutellidae) or on adult honeybees. Thus, all indications from this initial investigation are that OranNPV would be an important tool in the control of PAM in a future incursion of this species into New Zealand.     

Studies on ultrastructure and host range of aChlorella attacking virus

Summary A tail-less polygonal virus with a prominent capsid of about 140–150 nm in diameter and about 14–15 nm in thickness has been isolated from a freshwater pond. It shows a marked host specificity in attacking only an endosymbioticChlorella sp. isolated fromParamecium bursaria (Ciliata). Viral replication starts in the algal cytoplasm and both autospores and old cells are lysed. The ecology of the virus in the freshwater habitat is discussed. Screening tests for further phycoviruses were not successful.     

Deletions in the transmembrane domain of a sindbis virus glycoprotein alter virus infectivity, stability, and host range

The alphaviruses are composed of two icosahedral protein shells, one nested within the other. A membrane bilayer derived from the host cell is sandwiched between the protein shells. The protein shells are attached to one another by protein domains which extend one of the proteins of the outer shell through the membrane bilayer to attach to the inner shell. We have examined the interaction of the membrane-spanning domain of one of the membrane glycoproteins with the membrane bilayer and with other virus proteins in an attempt to understand the role this domain plays in virus assembly and function. Through incremental deletions, we have reduced the length of a virus membrane protein transmembrane domain from its normal 26 amino acids to 8 amino acids. We examined the effect of these deletions on the assembly and function of virus particles. We found that progressive truncations in the transmembrane domain profoundly affected production of infectious virus in a cyclic fashion. We also found that membrane composition effects protein-protein and protein-membrane interactions during virus assembly.     

Observations on the relationship between morphological variation and host range in populations of cereal cyst-nematode

British pathotype 3 of cereal cyst-nematode differs morphologically from Heterodera avenae. Mature cysts have a distinct underbridge which is absent from pathotypes 1 and 2. A population of pathotype 3 produced cysts on cereal genotypes resistant to pathotypes 1 and 2. The relationship of this pathotype to other graminaceous cyst-nematodes is discussed.     

A simple procedure to determine the infectivity and host range of viruses infecting anaerobic and hyperthermophilic microorganisms

Plaque assay is the method traditionally used to isolate and purify lytic viruses, to determine the viral titer and host range. Whereas most bacterioviruses are either temperate or lytic, the majority of known archeoviruses are not lytic (i.e. they are temperate or chronic). In view of the widespread occurrence of such viruses in extreme environments, we designed an original method, called the inverted spot test, to determine the host range and infectivity of viruses isolated from anaerobic hyperthermophilic and sulfur-reducing microorganisms. Here, we used this approach to prove for the first time the infectivity of Pyrococcus abyssi virus 1 (PAV1) and to confirm the host range of Thermococcus prieurii virus 1 (TPV1), the only two viruses isolated so far from any of the described marine hyperthermophilic archaea (Euryarchaeota phylum, Thermococcales order).     

Bacteriophage isolated from non-target bacteria demonstrates broad host range infectivity against multidrug-resistant bacteria

Antibiotic resistance represents a global health challenge. The emergence of multidrug-resistant (MDR) bacteria such as uropathogenic Escherichia coli (UPEC) has attracted significant attention due to increased MDR properties, even against the last line of antibiotics. Bacteriophage, or simply phage, represents an alternative treatment to antibiotics. However, phage applications still face some challenges, such as host range specificity and development of phage resistant mutants. In this study, using both UPEC and non-UPEC hosts, five different phages were isolated from wastewater. We found that the inclusion of commensal Escherichia coli as target hosts during screening improved the capacity to select phage with desirable characteristics for phage therapy. Whole-genome sequencing revealed that four out of five phages adopt strictly lytic lifestyles and are taxonomically related to different phage families belonging to the Myoviridae and Podoviridae. In comparison to single phage treatment, the application of phage cocktails targeting different cell surface receptors significantly enhanced the suppression of UPEC hosts. The emergence of phage-resistant mutants after single phage treatment was attributed to mutational changes in outer membrane protein components, suggesting the potential receptors recognized by these phages. The findings highlight the use of commensal E. coli as target hosts to isolate broad host range phage with infectivity against MDR bacteria.     

Observations on the survival and infectivity of airborne rinderpest virus

The most frequent means of spread of rinderpest, a cause of major epizootics and of great economic losses among cattle in the tropics, remains undetermined. Studies on airborne virus in vitro demonstrated survival for at least 30 min at low RH and a somewhat inferior period of survival at high RH; viability was greatly reduced at 50–60% RH. The infectivity of 3 strains of airborne rinderpest virus for cattle was demonstrated by a technique employing direct inhalation of viral aerosols.     

Influence of methods of preparation on the infectivity, agglutination, activity, and ultrastructure of bloodstream trypanosomes

Contrary to the reports of others, the surface coat of Trypanosoma brucei brucei was not removed by extensive washing in the various media investigated; in fact, other than a deformed profile when washed in saline, ultrastructure was little affected by column separation and washing in any of these media. Washing in saline increased the agglutinability but reduced the activity and infectivity of the organisms. Washing in bicine-buffered saline-glucose did not impair activity or infectivity but increased agglutinability, albeit to a lesser extent than after washing in phosphate-buffered saline-glucose. The inclusion of 0.1% serum or plasma in the washing medium (phosphate-buffered saline-glucose or bicine-buffered saline-glucose) increased the activity of the T. b. brucei and did not increase agglutinability or impair infectivity. T. congolense and T. vivax were more susceptible to ionic strength changes than were T. b. brucei or T. lewisi, in that not only was their activity impaired, but they began to aggregate on standing in lower ionic strength buffers.     

Evidence that the structural conformation of envelope gp120 affects human immunodeficiency virus type 1 infectivity, host range, and syncytium-forming ability.

We investigated how amino acid changes within and outside the V3 loop of the envelope glycoprotein of human immunodeficiency virus type 1 influence the infectivity, host range, and syncytium-forming ability of the virus. Our studies show that on the genomic backgrounds of the human immunodeficiency virus type 1 strains SF2 and SF13, a reciprocal exchange of full-loop sequences does not alter the syncytium-forming ability of the viruses, indicating that a determinant(s) for this biological property maps outside the loop. However, specific amino acid substitutions, both within and outside the V3 loop, resulted in loss of infectivity, host range, and syncytium-forming potential of the virus. Furthermore, it appears that a functional interaction of the V3 loop with regions in the C2 domain of envelope gp120 plays a role in determining these biological properties. Structural studies of mutant glycoproteins show that the mutations introduced affect the proper association of gp120 with the transmembrane glycoprotein gp41. Our results suggest that mutations that alter the structure of the V3 loop can affect the overall conformation of gp120 and that, reciprocally, the structure of the V3 loop is influenced by the conformation of other regions of gp120. Since the changes in the replicative potential, host range, and fusogenic ability of the mutant viruses correlate well with the changes in gp120 conformation, as monitored by the association of gp120 with gp41, our results support a close relationship between envelope gp120 structural conformation and the biological phenotype of the virus.     

Parasite host range and the evolution of host resistance

Parasite host range plays a pivotal role in the evolution and ecology of hosts and the emergence of infectious disease. Although the factors that promote host range and the epidemiological consequences of variation in host range are relatively well characterized, the effect of parasite host range on host resistance evolution is less well understood. In this study, we tested the impact of parasite host range on host resistance evolution. To do so, we used the host bacterium Pseudomonas fluorescens SBW25 and a diverse suite of coevolved viral parasites (lytic bacteriophage Φ2) with variable host ranges (defined here as the number of host genotypes that can be infected) as our experimental model organisms. Our results show that resistance evolution to coevolved phages occurred at a much lower rate than to ancestral phage (approximately 50% vs. 100%), but the host range of coevolved phages did not influence the likelihood of resistance evolution. We also show that the host range of both single parasites and populations of parasites does not affect the breadth of the resulting resistance range in a naïve host but that hosts that evolve resistance to single parasites are more likely to resist other (genetically) more closely related parasites as a correlated response. These findings have important implications for our understanding of resistance evolution in natural populations of bacteria and viruses and other host–parasite combinations with similar underlying infection genetics, as well as the development of phage therapy.     

Observations on the ultrastructure of the flagella and periplast in the Cryptophyceae

The flagella in Cryptomonas ovata Ehrenberg and two other un-named strains of Cryptomonas both bear stiff hairs with fine distal filaments of the same type as those found in the Xanthophyceae, the Chrysophyceae sensu stricto, the Phaeophyceae, the Bacillariophyceae, the Eustigmatophyceae and the Oomycetes. On the longer of the two flagella the hairs are 2·5 µm long and in two opposite rows whereas on the shorter flagellum they measure only 1 µm, are arranged in a single row and are more closely spaced. The long flagellum also bears a characteristic lateral swelling with a tuft of hairs of the same type as on the remainder of the flagellum, at approximately the level at which it emerges from the gullet. The hairs on the flagella of Hemiselmis rufescens Parke are distributed in a similar manner to those in Cryptomonas but they are more flexible and the swelling and tuft of hairs appear to be absent from the long flagellum. Hairs are apparently absent from the short flagellum of Chroomonas sp. The periplast in Cryptomonas ovata shows a hexagonal pattern in surface view and in sections of all three Cryptomonas strains appears as a typical plasmalemma underlain by a discontinuous layer of electron-dense material with variable substructure. The distribution of flagellar hairs and the structure of the periplast appear to be characters unique to the Cryptophyceae and these features emphasise the isolated position of this class of algae.     

Effects of host desiccation on development, survival, and infectivity of entomopathogenic nematode Steinernema carpocapsae

This study investigates the effect of host desiccation on entomopathogenic nematode (EPN) development, emergence, infectivity, and cross-protection against secondary environmental stress. Galleria mellonella hosts infected with the EPN Steinernema carpocapsae A10 were allowed to dehydrate in an environmental chamber for up to 56 days at 23 degrees C achieving a weight loss of approximately 86% by day 44 post-infection. Host carcasses were rehydrated on water-saturated filter paper in White traps to collect emergent infective juveniles (IJ) at specific time intervals. Populations were counted with an apparent peak coinciding with desiccated hosts rehydrated at 24-day post-infection. Desiccation-stressed IJ populations from each time interval were tested for infectivity, and cross-resistance to secondary temperature and pH stresses and were found to have significant increases in both infectivity and protection from extremes of temperature and pH compared with controls. Total aqueous soluble protein profiles from control and desiccation-stressed IJs were analyzed using 10% SDS Laemmli gels. Several novel proteins were over-expressed in EPN from hosts subjected to desiccation suggesting the induction and expression of stress response genes.     

Parvovirus host range,cell tropism and evolution

The past few years have seen major advances in our understanding of the controls of evolution, host range and cell tropism of parvoviruses. Notable findings have included the identification of the transferrin receptor TfR as the cell surface receptor for canine parvovirus and feline panleukopenia virus, and also the finding that specific binding to the canine TfR led to the emergence of canine parvovirus as a new pathogen in dogs. The structures of the adeno-associated virus-2 and porcine parvovirus capsids, along with those of the minute virus of mice, have also advanced our understanding of parvovirus biology. Structure-function studies have shown that in several different parvoviruses the threefold spikes or peaks of the capsid control several aspects of cell tropism and host range, and that those are subject to selective pressures leading to viral evolution. The cell and tissue tropisms of different adeno-associated virus serotypes were demonstrated to be due, in part, to specific receptor binding.     

Observations on the ultrastructure of developing myocardium of rat embryos

Timed pregnancies were obtained in Sprague-Dawley rats and early ultrastructural differentiation of myocardium of embryos of 10, 11, 12, 13, and 14 days was investigated and compared with that of newborn. Ten-day myocardium is characterized by loosely packed cells; the cytoplasm is typified by a dearth of organelles. Both thick (myosin) and thin (actin) filaments become identifiable for the first time in the 10-day myocardium where the heart is pulsating but circulation is not established. These filaments are not visible in the embryos of 9-day-old myocardium. The formation of these filaments is observed to continue throughout the period covered in this investigation. Concomitant with the appearance of the myofilaments is the synthesis of Z band material. By the eleventh day of gestation and during the subsequent days there is a rapid proliferation and differentiation of most of the organelles. The myofilaments become organized into fully formed striated fibrils. Intercalated discs appear as. small wavy lines on the eleventh day and become plicated in later stages and serve as cell boundaries and points of attachment for myofilaments and fibrils. There is a perceptible change in the number and morphology of mitochondria from the tenth to eleventh day and later stages of development when the heart becomes functional. Similarly, there is a rapid proliferation and differentiation of granular endoplasmic reticulum and Golgi bodies. Large quantities of free ribosomes are dispersed in the cytoplasm of 10-day myocardium; however, in later stages there is a progressive reduction in the distribution of these particles. An intimate association of ribosomes and polysomes with the developing myofibrils is discernible. The T -system and sarcoplasmic reticulum begin to appear in II-day myocardium. The embryonic myocardium displays intense mitotic activity throughout its development and a unique feature of embryonic myocardial cells is the simultaneous occurrence of myofilament synthesis and mitotic activity within the same cells.