Production and efficiency of protozoa

Despite the chronic and debilitative nature of the infection they cause, several species of microsporidia and neogregarines offer a good potential as microbial control agents, particularly against insect pests of high economic thresholds. Techniques for mass production of protozoa have usually involved per os, inoculation or injection of the protozoa into their usual or alternate hosts. The spores are harvested subsequently from heavily infected host tissues by grinding, filtration, and differential centrifugation. Although fresh spores are used in most field tests, the spores of many species can be stored with high survival either frozen or in water at low temperatures (0–4°C) for up to several months. Sunlight or ultraviolet (UV) radiation is a serious factor limiting spore persistence. However, the protozoa do not appear to be significantly limiting spore persistence. However, the protozoa do not appears to be significantly more susceptible to UV radiation than other insect pathogens and persistence can be prolonged with UV protectants. Most field tests with protozoa have involved the application of spores in sprays and have usually resulted in a high degree of infection in the target host species. The potential for control of few species has been improved by formulation of spores in to baits, and the potential of other species will likely increase if suitable bait formulation can be devised in the future. One species, Nosema locustae, formulated as a bait, has been successfully used to control grasshoppers on rangelands. Limited laboratory and field studies have also suggested that increased short-term control might be obtained if candidate protozoan species can be combined with certain insecticides. While recent and increased efforts have been devoted to assess the potential of protozoa as microbial control agents, potential hazards to nontarget organism have been investigated for only three species. Their close relation taxonomically to protozoa pathogenic for mammals will necessitate careful evaluation of the safety of candidate control species for nontarget organisms.     

New perspectives on protozoa

The interest of the British research community in protozoa has in the past emphasized the parasitic organisms-especially those causing diseases of economic importance in Africa. The last 20 years have witnessed dramatic changes in protozoology, and the purpose of this meeting was to indicate the nature and significance of these changes.
Three areas were discussed. The first was our present understanding of protozoan diversity and the evolution of protozoa (by David Patterson), the second (by Bland Finlay) presented some novel and ecological important symbiotic relationships between protozoa and other microorganisms), and finally Graham Coombs discussed the problems still being posed by parasitic protozoa and the application of new technologies to those problems.     

Polypeptides of hydrogenosome-enriched fractions from rumen ciliate protozoa and trichomonads: Immunological studies

Abstract The evolution of hydrogenosomes, energy-generating organelles of rumen ciliate protozoa and the flagellate trichomonads has been the subject of much speculation. Polypeptides of the hydrogenosome-enriched fractions from the rumen ciliates, Dasytricha ruminantium, Isostricha spp., Polyplastron multivesiculatum and Eudiplodinium maggii were separated by SDS-PAGE and compared to analogous polypeptide preparations from Tritrichomonas foetus . Immunoblotting with antisera specific to the hydrogenosomes of T. foetus identified common immunoreactive polypeptides present at estimated molecular masses of 28, 35, 38, 44, 48, 58, 100 and 120 kDa. That at 120 kDa corresponds to a single subunit of the purified pyruvate: ferredoxin oxidoreductase from the hydrogenosome of Trichomonas vaginalis .     

Frontiers in research on parasitic protozoa

Frontiers in research on parasitic protozoa was the theme of the Autumn Symposium of the British Section of the Society of Protozoologists, held 2 September 2002, in London, UK.     

Control of non-vector-borne protozoa

In conclusion it can be stated that bovine trichomoniasis and the various types of coccidioses can be fairly well controlled by the presently available methods. The problem of drug resistance in coccidiosis slightly decreased, following the introduction of the ionophorous coccidiostats but did not disappear. The search for new anticoccidial compounds has to be continued. Their finding is becoming increasingly difficult and expensive because new drugs are expected to have not only an anticoccidial activity but to have also a growth-promoting effect, and because safety regulations are becoming increasingly tougher. Due to public opinion against residues and a tendency towards more natural management systems, interest in immunological control measures has significantly increased in recent years. In spite of some effort no commercially expolitable vaccine has been brought forward so far. Modern methods like monoclonal antibody and recombinant DNA techniques are gradually being introduced into parasitological research and there is some hope that efforts will eventually succeed in producing safe and cheap vaccines. In the case of toxoplasmosis and sarcocystosis, much more basic research on the epizootiology and economic importance is needed before control measures can be recommended at a larger scale. There are some indications that the development of a vaccine at least against Toxoplasma-induced abortion in sheep is feasible.     

DNA of ciliated protozoa

DNA was isolated from macronuclei and micronuclei of the ciliated protozoan, Stylonychia mytilus under conditions that minimize the possibility of DNA degradation. Macronuclear DNA has an S value of 10 to 11 in sucrose gradients. Macronuclear DNA has an average molecular weight of 1.15×10⁶ daltons and a range of molecular weights of 1.0×10⁶ to 1.95×10⁶ daltons. The average length of macronuclear DNA, measured by electron microscopy, is 0.80 microns and the range is 0.2 to 2.2 microns. Almost all micronuclear DNA pieces are too long to be measured by electron microscopy. The shortest piece of micronuclear DNA found was 15.0 microns in length.     

N-Glycosylation in trypanosomatid protozoa

Trypanosomatid protozoa are parasites of considerable medicaland economic importance in developing countries. The pathwayleading to N-glycosylation in these micro-organisms is characterizedby the following features: (i) dolichols are composed of only10–13 isoprene units; (ii) oligosaccharides transferredin N-glycosylation have the compositions Man_{(6, 7, 9)}GlcNAc₂,depending on the species; (iii) trypanosomatids are unable tosynthesize dolichol-P-Glc and, in addition, some species lackcertain dolichol-P-Man-dependent mannosyltransferases; (iv)the oligosaccharyl-transferase does not require the presenceof glucose units in the oligosaccharide in order to catalysean efficient transfer reaction; (v) trypanosomatids have a glucosidaseII-like enzyme, but lack glucosidase I; (vi) glucosidase IIis required for deglucosylation of oligosaccharides glucosylatedby the UDP-Glc: glycoprotein glucosyltransferase, an activityfirst detected in those parasites; (vii) the structures of polymannose-typecompounds in these protozoa have no significant differenceswith those of their mammallan counterparts except for the presence,in certain species, of oligosaccharides having galactofuranoseunits linked to external mannose residues; (viii) biantennarycomplex-type oligosaccharides having in some cases terminal     

Viruses of parasitic protozoa

Associations are increasingly recognized between parasitic protozoa and smaller organisms such as bacteria (see Parasitology Today 1, 143), and viruses. Their revelation, originally by ultrastructural studies, may now be indicated by observations of 'rogue bands' on gel electrophoresis of parasite nucleic acids. The origins and roles of parasite 'parasites' are still uncertain, but, as Michael Miles suggests here, they may prove of particular importance as agents to introduce genes for important immunogens into non-pathogenic protozoa for vaccine delivery.