Letteratura scientifica selezionata sul tema "Host-parasite relationships"

The nocardiae are bacteria belonging to the aerobic actinomycetes. They are an important part of the normal soil microflora worldwide. The type species, Nocardia asteroides, and N. brasiliensis, N. farcinica, N. otitidiscaviarum, N. nova, and N. transvalensis cause a variety of diseases in both normal and immunocompromised humans and animals. The mechanisms of pathogenesis are complex, not fully understood, and include the capacity to evade or neutralize the myriad microbicidal activities of the host. The relative virulence of N. asteroides correlates with the ability to inhibit phagosome-lysosome fusion in phagocytes; to neutralize phagosomal acidification; to detoxify the microbicidal products of oxidative metabolism; to modify phagocyte function; to grow within phagocytic cells; and to attach to, penetrate, and grow within host cells. Both activated macrophages and immunologically specific T lymphocytes constitute the major mechanisms for host resistance to nocardial infection, whereas B lymphocytes and humoral immunity do not appear to be as important in protecting the host. Thus, the nocardiae are facultative intracellular pathogens that can persist within the host, probably in a cryptic form (L-form), for life. Silent invasion of brain cells by some Nocardia strains can induce neurodegeneration in experimental animals; however, the role of nocardiae in neurodegenerative diseases in humans needs to be investigated.

The ability of Leiophron uniformis (Gahan) to parasitize 4 Lygus spp. was determined. While L. uniformis readily attacked Lygus hesperus (Knight), L. lineolaris (Palisot de Beauvois), L. elisus Van Duzee, and L. desertinus Knight, only 6.7% of the L. lineolaris attacked were parasitized compared to 84-87% parasitization of the other species. Two factors were found to cause the low rate of parasitism of L. lineolaris. L. uniformis oviposited in (accepted) few of the L. lineolaris nymphs attacked and most eggs found were encapsulated by the host. Nymphs less than 48-hr old were readily parasitized because they were accepted by the wasps and the hosts encapsulated few of the parasitoid eggs. As nymphal age increased, parasitism dropped rapidly as the acceptance of the host decreased and the host's encapsulation ability increased. Different strains of L. lineolaris were found to differ greatly in their susceptibility to parasitism, their ability to encapsulate, and their acceptance by the parasitoids. A host strain from Arizona was very resistant to parasitism, whereas a strain from Delaware (NJLBR) that had been in culture for 7 years was easily parasitized. The NJLBR strain had no encapsulating ability and it was readily accepted by L. uniformis. A recently established host strain from Delaware (DELBR) encapsulated 23-27% of the parasitoid eggs while an Arizona strain (FILBR) encapsulated 66-76% of the eggs. The DELBR nymphs were accepted in 42-43% of the attacks while the FILBR nymphs were accepted in only 5-14% of the attacks. Delaware and California parasitoid strains did not differ in their acceptance of L. lineolaris or in their ability to resist encapsulation. Rearing L. uniformis for only 1 generation on L. lineolaris did not precondition the wasps to accept that species as a host in preference to L. hesperus. L. uniformis, which had been reared on L. lineolaris for 5 or more generations, did accept that host 2.5 times as often as wasps reared on L. hesperus. The parasitoids did not known any increase in resistance to encapsulation even after they had been reared on L. lineolaris for 11 generations.

Pomatoschistus microps at Salthouse Point, Burry Inlet, Wales return to the estuary and spawn during June, the 1-group adults then disappear and presumably die but the developing juveniles become heavily parasitized with overdispersed, innocuous, encysted digenean metacercariae namely Cryptocotyle jejuna and C.lingua in subcutaneous muscle, C.concava (Heterophydae), in the body cavity, Labratrema minimus (Bucephalidae), in the liver, Timoniella imbutiforme and T.praeterita (Acanthostoidae) in subcutaneous muscle. Host weight, condition and other growth parameters do not appear to be affected by these parasites. However, declining rates of heterophyid infections after August suggest that host defence responses or hyperparasitism may kill some parasites. Gobies leave the estuary after November and, as suggested by increasing C.lingua and L.minimus infections, may migrate to overwinter near West Cross, Swansea Bay. Sixteen allozyme loci were resolved in these fish, using gel electrophoresis based on a sample of 575 fish. Five of these loci are polymorphic namely LDH, IDH, PGM-1, PGM-2 and PGI. The mean heterozygosity per locus is 0.06 - 0.004 and individual heterozygosity is not usually correlated with host growth parameters but is usually negatively correlated with parasite burden. The relationship is statistically significant, however, only with C.jejuna in September, the sole parasite species which elicits an intense melanized host defence response namely 'black spot' disease. The possible reasons for this are discussed in detail. In Pomatoschistus minutus at Oldbury, Severn Estuary, very lightly parasitized with the larvae of Ligula intestinalis (Cestoda: Pseudophyllidea) and Hysterothylacium sp. (Nematoda: Anisakidae), five of seventeen loci are polymorphic. The mean heterozygosity per locus is 0.03 - 0.014. The results provide equivocal support for the parasite version of the Red Queen hypothesis which predicts that the most heavily parasitized populations will have the highest mean heterozygosity and, within populations, individuals with least parasites will have highest heterozygosity.

The BacA protein plays a key role in the symbiosis of Sinorhizobium meliloti with the leguminous plant alfalfa (Medicago sativa) and is proposed to be the transmembrane subunit of an ATP‐binding cassette (ABC) transporter. BacA homologues are also present in Brucella species, enteric bacteria (known as SbmA) and Mycobacterium tuberculosis. The S. meliloti‐alfalfa symbiosis, although beneficial to both partners, can also be viewed as a chronic infection. The M. tuberculosis BacA protein is important for M. tuberculosis for the maintenance of a chronic infection. In order to study the M. tuberculosis BacA protein a codon optimised M. tuberculosis bacA gene was synthesised and cloned into vectors for expression in an S. meliloti ΔbacA mutant. Evidence is presented that M. tuberculosis BacA sensitises an S. meliloti ΔbacA mutant towards the glycopeptide bleomycin and the truncated proline rich peptide Bac71‐16, and further that a functional ATPase domain is essential to perform BacA mediated peptide transport. The M. tuberculosis BacA protein protected an S. meliloti ΔbacA mutant from being killed by host defensins. In addition, it was determined that M. tuberculosis BacA‐mediated protection of the legume symbiont S. meliloti against legume defensins as well as mouse alveolar lavages and human ‐defensin 2 is dependent on an ATPase domain which is present in the M. tuberculosis BacA protein. M. tuberculosis encounters ‐defensins during mammalian infections in the host’s lungs and my data show that BacA is likely to be important in conferring immunity to these peptides. The mechanism of persistent infection by M. tuberculosis is therefore very reminiscent of the Sinorhizobium ‐ legume interaction. Also Salmonella enterica is able to cause asymptomatic infections and about 5% of these develop a chronic carrier state and are able to spread the pathogen. In enteric bacterial species SbmA is in close proximity to the putative lipoprotein YaiW. In this study it was determined that YaiW is exposed on the cell surface and that it is involved in the protection of E. coli and potentially Salmonella spp. against a cysteine rich host peptide. YaiW is potentially involved in swarming motility. It was also determined that an alfalfa plant infection model can distinguish between Salmonella strains forming acute and chronic infections. Staphylococcus aureus is one of the major hospital acquired and opportunistic pathogens. Asymptomatic carriers, infected with multi‐drug resistant strains (MRSA) pose a threat to immunocompromised individuals. Here, novel compounds and ways from a variety of sources have been tested for their potential antimicrobial activity against a range of multi‐drug resistant clinical S. aureus isolates. This project significantly advanced the molecular understanding of asymptomatic bacteria‐host infections and helped to understand and establish novel ways to treat infections with multi‐drug resistant clinical pathogens.

This study has investigated the nature of host derived cues used by parous female C. impunctatus in the location of blood meal hosts. Olfaction has been shown to be a vital part of the process. The responses of antennal receptors of females to a variety of host-derived volatile compounds were assessed using the EAG technique. High antennal sensitivity to olfactory cues was indicated by low thresholds for response and, taking into account the volatility of the compounds, a clear hierarchy of response was obtained in which octenol was the most stimulatory, followed by phenolics, lactic acid and finally ketones. Of particular note with regard to phenolic compounds was the finding that 3-derivatives (3-n-propylphenol & 3-methylphenol) were more stimulatory than their 4-derivatives (eg 4-methylphenol). Behavioural assays conducted within a Y-tube olfactometer showed that attraction to olfactory cues was dose dependent. Supra optimal doses which caused receptor saturation (as demonstrated in the EAG assay), also induced marked changes in behaviour with responses being either no different to random expectation, or the compound appearing to be repellent. Wind tunnel assays corroborated these findings for octenol and acetone when used in conjunction with 0.01% CO₂. Upwind flight was found to be maximal, and significantly different from responses to the CO₂ standard, at concentrations within the tunnel of 1.33x10^-8 g 1^-1 and 1.5x10^-6 g 1^-1, respectively. These concentrations are approximately those released by a bovid host for octenol and 1/1000x for acetone. Females exhibited a linear dose dependent response to increases in the concentration of CO₂ in the wind tunnel up to 0.09% whether gas was released as a plume or as a lightly turbulent cloud. However, at cloud concentrations above this, CNS mediated habituation is suggested to have arrested upwind flight.

This thesis examines a broad spectrum of physiological and silvicultural features of the highly valued woody angiosperm hemi-parasite Santalurn album L. (Indian sandalwood) in relation to its culture in plantations in northern Western Australia. Topics covered include allometry of host and Santalum when grown as single plant pairings in both field and pot culture, nutritional interactions between Santalum and beneficial and non-beneficial hosts, deleterious influences of parasitism on plantation productivity and heartwood induction in young trees. In Western Australia sandalwood is grown in the nursery for 8 months before establishment in the field and during this time a pot host is introduced. Survival of Santalurn after field establishment and its subsequent growth were significantly affected by the time of introduction of the pot host, Alternanthera nana. Increasing the period of the Santalum : Alternanthera association in the nursery to 109 days prior to field establishment markedly increased early growth of Salztalum plantations. Introduction at 134 days prior to field establishment was detrimental to the parasite as the Alternanthera was too vigorous for the small Santalum seedlings. Santalurn plants had a lower root : shoot ratio lower when cultured with Alternanthera in the nursery prior to field establishment compared with seedlings grown without Alternanthera. Alterrzantlzera survival in the field was high when it had been grown with Santalum for 12 weeks or more in the nursery prior to field establishment. After 1 1 weeks in the field a strong negative linear relationship was shown between Santalunz root : shoot ratio and Alternarzthera dry weight, and a positive linear relationship between Salztalum DW and Alternanthera DW. In Western Australia Santalu~n is established in the field with an intermediate host which nourishes the parasite for 3-5 years before Santalum becomes dependent on its long-term host and the intermediate host dies. The relationship between Santalum and several species tested as intermediate hosts was examined by pairing Santalum seedlings with intermediate host seedlings in 25 litre pots over a 10 month period. Growth of Santalum in pot culture with three N2-fixing woody intermediate hosts (Sesbania forrnosa, Acacia traclzycarpa and A. ampliceps), the woody non N2-fixing Eucalyptus camaldulensis or without a host varied considerably between host treatments. Santalum growth was greater and root : shoot ratio lower for seedlings grown with N2-fixing hosts compared with seedlings grown with E. carnaldulensis or with no host. The root : shoot ratio of unattached Santalum increased exponentially over time, whereas for all other treatments it remained relatively constant. An assessment of the value of the hosts, termed host use efficiency, was computed as Santalum shoot DW / host shoot DW. The host use efficiency of A. trachycalpa was greater than that of the other hosts. The xylem sap of hosts and Sarztalum, and ethanolic extracts of endophytic tissue of haustoria of Santalzkm were analysed for amino acids, organic acids and sugars to determine which solutes were available in the host and which were extracted by the Santalum haustoria from different hosts. There were similarities between Santalum and legume hosts in concentration and composition of xylem sap amino acids, and in the amino acid spectra of the corresponding Santalum endophytic tissue, whereas there were low N levels in xylem sap of E. camaldulensis and dissimilarities between its amino acid composition and that of Santalum. This indicated substantial direct intake of xylem N by Santalum from legume hosts but little N from the xylem sap of E. canzaldulensis. There were high concentrations of asparagine, glutamate, aspartate and y-amino glutamate in the xylem sap of the legume hosts, while in the non-legume the most common amino acids were glutamate, aspartate, glutamine and arginine. Proline, the predominant amino acid in the xylem sap of Santalum acurninatum growing in natural vegetation (Tennakoon et al. 1997) was not detected or present in very low concentrations in Santalurn album under these conditions. in the non-legume. Xylem sap of hosts contained variable amounts of sugars (sucrose, glucose and fructose) and organic acids (fumaric, citric and malic acid), whereas that of the parasitic Santalum was dominated by fructose and malic acid. Dissimilarities in the proportional amounts of xylem-borne sugars and organic acids were particularly evident for the E. camaldulensis : Santalum partnership. Diurnal profiles of photosynthesis and transpiration of Santalum were closely similar to those for corresponding hosts, whereas the midday leaf water potential of Santalum was consistently more negative than that of corresponding hosts. Net photosynthesis and water use efficiency was lower, but transpiration rates were similar to that of corresponding hosts. Nitrogen concentrations of foliage of Santalum were higher than their hosts, and higher when on legume hosts than on E. camaldulensis, or without a host. Nitrogen concentrations of Santalum foliage was strongly correlated with net photosynthesis and water use efficiency of Santalum. 813C values of shoot dry matter of Santalum were poorly correlated with instantaneous water use efficiency of Santalum. Tissue water relations of Santalum were similar to that of water-stress tolerant species. S. formosa proved the best host followed by Acacia ampliceps and A. traclzycarpa based on dry matter gains of Santalum. Estimates of heterotrophic gain of C of Santalum when grown in association with the legume hosts over a nine week period indicate 57.9% of C was derived from A. ampliceps, 45.5% from A. trachycarpa and 34.6% fiom S. fomosa. Abundance of haustorial attachments on roots of hosts was poorly correlated to Santalum shoot DW. Root nodules of legume hosts were parasitised by a small proportion of Santalum haustoria. Sodium and phosphorus concentrations of foliage of Santalum were generally higher than that of corresponding hosts. Net gains of calcium, potassium, phosphorus and sodium in Santalum was greatest when grown in association with hosts richest in the corresponding element. Net losses or only small gains of calcium, potassium, phosphorus and sodium were recorded when Santalum was grown with E. camaldulensis or without a host suggesting that Santalum has limited ability for uptake of those minerals through its own root system. To understand the effect of hosts on the productivity of a Santalum plantation a young plantation of Santalum with three host species Cathormion umbellatum, Sesbania formosa and Acacia anuera was selected to study the relationship between host quality and distance of hosts from Santalunz on Santalum health. The selected plantation showed marked decline in health and vigour of both Santalum and hosts between years 3 and 5. Parameters of the host plants were assessed to select the best predictor of Santalunz crown health. The height and diameter growth increment of Santalum between years 3 and 5 was strongly correlated to Santalum crown health. Santaluin crown health and growth increased as host quality increased, and the distance of host fiom Santalum decreased. An index, which combined host quality and the distance of the host from that of Santalum, was a better predictor of Santalum crown health than host distance or quality alone. The age at which heartwood is initiated in Santalum album under plantation conditions in Western Australia in unknown, but in natural stands in India it occurs between 10-13 years of age (Rai 1990). A field experiment was conducted to determine the efficacy of stem injections of paraquat andlor ethrel in initiating heartwood formation in five year old Santalum trees in a plantation. Trees injected with paraquat alone had a significantly greater extension of induced heartwood, both radially and vertically, than those trees injected with ethrel alone or distilled water. Eight months after treatment with paraquat or ethrel or a combination of these chemicals induced heartwood was formed, which had high lipid, and low starch and polysaccharide concentrations compared to the sapwood. Induced heartwood from both chemical treatments and their combinations contained total volatile oil and santalol oil (alpha and beta santalol) concentrations that were equal to or greater than that of naturally formed heartwood and greater than that of sapwood. Moisture content, and concentrations of K and Mg, and in some treatments Ca of induced heartwood were significantly lower than that of sapwood. The thesis concludes with a synthesis of the findings and suggestions for future research, with special reference to mid-rotation aspects of Santaltrm plantation silviculture.

Hemisarcoptes (Acari: Hamisarcoptidae) is a parasite of scale insects (Diaspididae), tenacious pests of vascular plants. Hemisarcoptes also has a stenoxenic phoretic (dispersal) relationship with Chilocorus (Coleoptera: Coccinellidae). Chilocorus feeds on diaspidids, transports mites as they feed, and has been applied to the control of scales, with limited success. U.S.-Israeli cooperation focused on this mite-beetle interaction so that a two-component system could be applied to the control of scale insects effectively. Life history patterns of Hemisarcoptes were investigated in response to host plant type and physical parameters. Field and lab data indicated that mites attack all host stages of scales tested, but preferred adult females. Scale species and host plant species influenced the bionomics of Hemisarcoptes. Beetle diet also influenced survival of phoretic mites. Mites use a ventral sucker plate to extract material from Chilocorus, that is essential for development. Seven alkaloids were found in the hemolymph of Chilocorus and three were characterized. Examination of the subelytral surface of Chilocorus indicated that microsetae play a role in the number and distribution of mites a beetle transports. While Hemisarcoptes can be innoculatd into agroecosystems using various indigenous or imported Chilocorus species, the following are preferred: C. bipustulatus, C. cacti, C. distigma, C. fraternus, C. orbus, and C. tristis.