Screening for Indian isolates of predacious fungi for use in biological control against nematode parasites of ruminants

Genetic manipulations in helminth parasites

Screening of vaccine or drug target in parasitic helminth is hindered by lack of robust tool for functional studies of parasite protein which account for the availability of only a few anti-helminthic vaccines, diagnostic assay and slower pace of development of an anthelmintic drug. With the piling up of parasite transcriptomic and genomic data, in silico screening for possible vaccine/drug target could be validated by functional characterization of proteins by RNA interference or CRISPR/Cas9. These reverse genetic engineering tools have opened up a better avenue and opportunity for screening parasitic proteins in vitro as well as in vivo. RNA interference provides a technique for silencing targeted mRNA transcript for understanding a gene function in helminth as evidence by work in Caenorhabditis elegans. Recent genetic engineering tool, CRISPR/Cas9 allows knock-out/deletion of the desired gene in parasitic helminths and the other provision it provides in terms of gene knock-in/insertion in parasite genome is still to be explored in future. This manuscript discussed the work that has been carried out on RNAi and CRISPR/Cas9 for functional studies of helminth parasitic proteins.

Isolation of nematophagous fungi from soil samples collected from three different agro-ecologies of Ethiopia

Background

Several species of nematophagous fungi exist in nature that can capture and kill nematodes as natural predators of soil-dwelling worms. These are important in agriculture and animal husbandry as biological control agents. The diversity of nematophagous fungi found from soil had not been studied in Ethiopia.

Objective

This study aimed to isolate Nematophagous Fungi from Soil Samples Collected From three Different Agro-Ecologies of Ethiopia.

Methods

Cross-sectional study was conducted and samples were collected from three different agro-climatic zones of Ethiopia; Debre-Berhan (highland), Bishoftu (mid-altitude), and Awash (lowland). Twenty-seven soil samples were randomly taken from each of the three different agro-ecological climates (9 from each agro-ecological climatic zone). For each study site, samples were collected from the soil of decomposed animal feces/dung, agricultural/farmlands, and forest lands in triplicates.

Results

The present study disclosed that nematophagous fungi were widespread from the study area. A total of 33 species of nematophagous fungi belonging to four genera, Arthrobotryes, Paecilomyces, Monacrosporium, and Harposporium were identified. Arthrobotrys were the most commonly isolated genera followed by Paecilomyces. The six identified species were Arthrobotrys oligospora, Paecilomyces lilacinus, Arthrobotryes dactyloides, Monacosporum eudermatum, Harposporium helicoides, and Monacosporum cionopagum.

Conclusion

This study indicated that Arthrobothryes oligospora was the most common species in Bishoftu and Awash whereas. In Debre-Berhan, Paecilomyces lilacinus was the most prevalent species. Monacosporum cionapagum was not isolated from dung soil and agricultural soil whereas Harposporium helicoides and Arthrobothryes dactyloides were not found from dung and forest soil respectively.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02572-4.

Morphological variability, molecular phylogeny, and biological characteristics of the nematophagous fungus Duddingtonia flagrans

This study aims to investigate the molecular phylogenetic analysis, morphological variability, nematode-capturing ability, and other biological properties of Chinese Duddingtonia flagrans isolates. We isolated 13 isolates of D. flagrans and found features that have never been reported before, such as two to three septa incluing club-shaped conidia. Meanwhile, we conducted molecular phylogenetic analysis of the seven isolates and tested the radical growth of the isolates under different pH values, temperatures, and media. The capturing ability against infective larvae (L3) of Cooperia spp. in yak was detected in vitro. Finally, one isolate was selected for scanning electron microscopy (SEM) to investigate the trap formation process. The fungal sequence was obtained and submitted to GenBank (Accession no. KY288614.1, KU881774.1, KP257593.1, KY419119.1, MF488979.1, MF488980.1, and MF488981.1), and the tested isolates were identified as D. flagrans. Except for three isolates, the radial growth of the other isolates on 2% corn meal agar and 2% water agar exhibited faster growth than on other media. The fungus could not grow at 10 and 40°C but grew within 11 to 30°C. Moreover, it did not grow at pH 1-3 and 13-14, but instead at pH 4-12. In the in vitro experimental, L3s were reduced by 94.36%, 88.15%, and 91.04% for SDH035, DH055, and F088, respectively. SEM results showed that at 8 hr post addition of nematodes, some of the latter were captured. In the later stages of the interaction of the fungus with nematodes, a large number of chlamydospores were produced, especially on the predation trap. Results of the present study provided information about the molecular phylogenetic analysis, morphological variability, nematode-capturing ability, and other biological properties of Chinese Arthrobotrys flagrans isolates before administering them for biocontrol.

Isolation and characterization of the nematophagous fungus Arthrobotrys conoides

The spread of organic farming and the development of resistance to anthelmintics by parasites, especially in small ruminants, have necessitated the search for alternative methods of nematode control. Biological control using nematophagous fungi is one option; however, few studies have been conducted with native strains. The present study was divided into two phases. In the first phase, we aimed to isolate, identify, and assess the in vitro predatory activity of nematophagous fungi that had been isolated on Trichostrongylidae third-instar larvae. In the second phase, the isolate with superior predatory activity in vitro was molecularly characterized, and its morphological plasticity was observed using scanning electron microscopy (SEM) on Haemonchus third-instar larvae. Of the 56 soil samples from different regions of Paraná State, Brazil, 57 fungal strains were recovered, of which four exhibited predatory activity. Two pure isolates were obtained: the CED and LIN strains. After demonstrating 96.35 % predatory activity for the CED strain, this strain was selected and characterized using molecular criteria by sequencing the rDNA internal transcribed spacer and was identified as Arthrobotrys conoides (GenBank ID: JN191309). Morphological patterns in this strain during the interaction between the fungus and the nematode were revealed by SEM, in which two extensions of the infection bulb that was used to pierce the nematode's cuticle were clearly visible.

Fungus–benzimidazole interactions: a prerequisite to deploying egg-parasitic fungi Paecilomyces lilacinus and Verticillium chlamydosporium as biocontrol agents against fascioliasis and amphistomiasis in ruminant livestock

In vitro trials investigating the effects of albendazole and triclabendazole anthelmintics on the growth profiles of the egg-parasitic fungi Paecilomyces lilacinus and Verticillium chlamydosporium were undertaken. In addition, in vivo trials were conducted in goats fed on millet grain cultures of each fungus and administered albendazole and triclabendazole anthelmintics. In vitro growth revealed V. chlamydosporium to be more sensitive to albendazole compared to P. lilacinus. In contrast, triclabendazole had the least inhibitory effect on in vitro growth of both P. lilacinus and V. chlamydosporium. Similar to albendazole, growth of P. lilacinus was more vigorous at 0.5 ppm concentration of triclabendazole. Efforts to re-isolate these egg-parasitic fungi from faeces of goats fed on fungal millet grain cultures before and following single intraruminal administration of albendazole and triclabendazole showed that P. lilacinus was not able to be re-isolated from the faeces at any sampling period. In contrast, V. chlamydosporium was able to be re-isolated from the faeces at all of the sampling periods except for the samples taken at 8–18 h and 18–24 h after administration of albendazole and triclabendazole, respectively. Lack of fungal activity at these times coincided with peak plasma availability of anthelmintics and suggests faecal levels of drugs were also high at these times and impacted negatively on fungal viability.

Screening for Indian isolates of egg-parasitic fungi for use in biological control of fascioliasis and amphistomiasis in ruminant livestock

Wild isolates of the egg-parasitic fungiPaecilomyces lilacinusandVerticillium chlamydosporium, obtained from the organic environment of Durg, Chhattisgarh, India, were subjected to screening forin vitrogrowth using different media types, range of incubation temperature and pH, and their predatory activity to the eggs ofFasciola giganticaandGigantocotyle explanatum. Maximum growth ofP. lilacinuswas obtained in corn-meal agar compared to any other media types. The preferred medium for growth ofV. chlamydosporiumwas corn-meal agar, followed by potato-dextrose agar. After initial growth for 16 h of incubation, no growth was observed in water agar for both the fungi. Six different temperatures – 4°C, 10°C, 18°C, 26°C, 34°C and 40°C – were used to observe growth profiles of the fungi in corn-meal agar medium. While no and very little growth ofP. lilacinusandV. chlamydosporiumwas observed at 4°C and 10°C, respectively, growth profiles of both the fungi were optimal at 26–40°C. A range of pH (pH 4–8) supported growth of bothP. lilacinusandV. chlamydosporium. Full-grown plates of the fungi baited with viable eggs ofF. giganticaandG. explanatumrevealed thatV. chlamydosporiumwas more vigorous in its egg-parasitic ability compared toP. lilacinus. Distortion of the eggs started on day 2–3 of egg baiting in culture plates ofV. chlamydosporium, with complete distortion by day 7. On the contrary,P. lilacinusexhibited very limited egg-parasitic ability and some of the baited eggs even showed development of miracidia.

Formulation of a strategy for the application of Duddingtonia flagrans to control caprine parasitic gastroenteritis

Experiments on the influence of egg density and varying quantities of chlamydospores on the nematode-trapping ability of Duddingtonia flagrans, influence of D. flagrans on the larval translation of gastrointestinal nematodes, doses of chlamydospores required for the effective control of gastrointestinal nematodosis and the epidemiology of nematode parasites were conducted in goats, which generated baseline data required for strategic application of the biocontrol agent. The nematode-trapping ability of D. flagrans, measured by numerical enumeration of infective third-stage larvae developed in the faecal culture, revealed that the efficacy is dependent on both nematode egg and chlamydospore density. Pasture plot studies revealed that D. flagrans, if deposited at the same time as nematode eggs, prevents translation of third-stage larvae of caprine nematodes from the faecal pats onto the grass blades. Feeding of 1 × 106 chlamydospores per kg body weight and above to goats virtually eliminated larvae from the pasture. Application of as few as 1 × 104 and 1 × 105 chlamydospores per kg body weight had a profound impact on larval recovery. The effect persisted as long as the chlamydospores were fed. Monthly faecal worm egg counts of adult goats maintained under a semi-intensive management system on the Chhattisgarh plain and pasture larval burden revealed that June to August were the months of high risk for nematodosis. Haemonchus was the dominant species recorded throughout the year. The present data can best be utilized by formulating a strategic control measure when the larval challenge to the animal is maximum (June to August), so as to prevent establishment of patent infection. The observations reinforced the strategy to be adopted for nematode parasite control in goats by applying the biocontrol option at the onset of the monsoon.

The nematode-trapping efficacy of two chlamydospore-forming fungi against Haemonchus contortus in sheep

An in vitro study was carried out to determine efficacy of Indian isolates of the nematode-trapping fungi Arthrobotrys musiformis and Duddingtonia flagrans to capture infective larvae of Haemonchus contortus. These fungi have previously been screened and selected for their survival in the gastrointestinal tract of sheep without losing growth and nematode capturing potential. Following the feeding of chlamydospores of these two fungi alone or in combination in sheep experimentally infected with Haemonchus contortus, coprocultures were set up to enumerate the infective third stage larvae. The number of larvae captured from faeces of fungus-fed sheep was significantly higher compared with fungus-unfed controls irrespective of the fungus used. The fungal combination produced no antagonistic effect and thus can be used as efficiently as the fungi alone in the biological control of animal parasitic nematodes.

The predatory capability of Arthrobotrys cladodes var. macroides in the control of Haemonchus contortus infective larvae

One hundred compost samples were examined for the presence of nematophagous fungi on the sheep farms of Mazanderan, province, Iran. Arthrobotrys cladodes var. macroides (IRAN 677C=CBS 143565) was isolated from 3% of the samples examined. Nematophagous activity of this fungus which was shown for the first time in this study, revealed the addition of 1000, 8000, 20000 and 100000 conidia per gram of feces of sheep reduced significantly (P<0.001) the number of Haemonchus contortus infective larvae in the feces by 41.71%, 63, 27%, 73.49% and 94.96%, respectively. These results show that A. cladodes var. macroides is a promising candidate for biological control of H. contortus.

Top dressing of feed with desiccated chlamydospores of Duddingtonia flagrans for biological control of the pre-parasitic stages of ovine Haemonchus contortus

Feeding trials were conducted with stall-fed sheep parasitized with Haemonchus contortus. For 10 days they were offered 250 g of a concentrate feed that had been top-dressed with desiccated chlamydospores of Duddingtonia flagrans at 1 x 10(5), 5 x 10(5), 1 x 10(6) or 2 x 10(6) chlamydospores/kg body weight. Pooled faeces from each group on day 7 of spore feeding were spread on different pasture plots. On day 28 after the start of spore feeding, further pooled faeces from each group were spread on the same plots. The larval burdens on the plots were monitored for 2 months and the larval harvest from in vitro faecal cultures were monitored regularly. The application of 1 x 10(6) or more spores/kg body weight virtually eliminated larvae from both the pasture and the faecal cultures. The application of as few as 1 x 10(5) spores/kg body weight had a profound impact on larval recovery. The effect persisted while the spores were being fed but not for more than 4 days following discontinuation of spore feeding. Top dressing supplementary feed with dried chlamydospores offers a potential way of using D. flagrans for biological control of the pre-parasitic stages of H. contortus.