Beerntsen BT et al. (1989) J Parasitol "Brugia malayi and Brugia pahangi: inherent difference in immune activation in the mosquitoes Armigeres subalbatus and Aedes aegypti."

Beerntsen BT, Luckhart S, Christensen BM

[J Parasitol, 1989]

The inherent ability of Brugia malayi and Brugia pahangi (Nematoda) to establish successful relationships with the mosquitoes Armigeres subalbatus and Aedes aegypti Liverpool strain was evaluated. Brugia pahangi microfilariae (mff) avoided the immune response and developed normally in A. subalbatus exposed to the parasite by an infective bloodmeal, whereas nearly 85% of B. malayi were destroyed by the immune response. Because A. aegypti supports the development of both filarial worm species but destroys intrathoracically inoculated B. pahangi isolated from jird blood, blood-isolated B. malayi were inoculated into A. aegypti, and the immune response was compared with that observed against B. pahangi. The response against B. malayi was significantly more rapid and effective than the response against B. pahangi. Similar results were obtained when blood-isolated B. pahangi or B. malayi were inoculated into A. subalbatus. Microfilariae of both species were able to avoid immune destruction in A. aegypti if they were allowed to penetrate the Liverpool midgut in vitro prior to inoculation. Most B. pahangi that had first penetrated an Armigeres midgut prior to inoculation into A. subalbatus were able to avoid the immune response, but by day 3 postinoculation, less than 40% of the B. malayi, treated in the same manner, were able to escape the immune response. Genetic susceptibility of mosquitoes to infection by filarial worms and potential mechanisms of immune evasion/suppression are discussed regarding B. malayi and B. pahangi.

Beerntsen BT et al. (2007) J Med Entomol "Response of Armigeres subalbatus (Diptera: Culicidae) to intraperitoneally isolated Brugia spp. microfilariae."

Lowery RJ, Beerntsen BT

[J Med Entomol, 2007]

The relationship between mosquito and parasite involves a delicate balance that is influenced not only by the mosquito but also by parasite determinants. Using the biologically and morphologically similar parasites Brugia malayi and Brugia pahangi and the mosquito Armigeres subalbatus (Coquillett) (Diptera: Culicidae), it should be possible to dissect out the key elements involved in initiating or avoiding an immune response, known as melanotic encapsulation, because in this mosquito B. malayi microfilariae (mf) are melanized and destroyed, but B. pahangi mf develop normally into infective-stage larvae. Because of limitations in isolating sufficient mf from the circulation of an infected mammalian host, Brugia spp. mf that can be obtained in large numbers from the peritoneal cavity of an infected host were tested to ascertain the immune response of Ar. subalbatus to this source of mf. Results indicate that the immune response of Ar. subalbatus against intraperitoneal (i.p.) Brugia spp. mf mimics that which is observed when this mosquito is exposed to mf-infected animals, indicating that i.p. mf are similar to those mf that circulate naturally in the blood of the vertebrate host. Therefore, the i.p. mf should serve as an excellent source of material for genomic and proteomic studies designed to analyze the role of the parasite in influencing the immune response of the mosquito.

Marroquin LD et al. (2000) Genetics "Bacillus thuringiensis (Bt) toxin susceptibility and isolation of resistance mutants in the nematode Caenorhabditis elegans."

Elyassnia D, Feitelson JS, Griffitts JS, Marroquin LD, Aroian RV

[Genetics, 2000]

The protein toxins produced by Bacillus thuringiensis (Bt) are the most widely used natural insecticides in agriculture. Despite successful and extensive use of these toxins in transgenic crops, little is known about toxicity and resistance pathways in target insects since these organisms are not ideal for molecular genetic studies. To address this limitation and to investigate the potential use of these toxins to control parasitic nematodes, we are studying Bt toxin action and resistance in Caenorhabditis elegans. We demonstrate for the first time that a single Bt toxin can target a nematode. When fed Bt toxin, C. elegans hermaphrodites undergo extensive damage to the gut, a decrease in fertility, and death, consistent with toxin effects in insects. We have screened for and isolated 10 recessive mutants that resist the toxin's effects on the intestine, on fertility, and on viability. These mutants define five genes, indicating that more components are required for Bt toxicity than previously known. We find that a second, unrelated nematicidal Bt toxin may utilize a different toxicity pathway. Our data indicate that C. elegans can be used to undertake detailed molecular genetic analysis of Bt toxin pathways and that Bt toxins hold promise as nematicides.

Griffitts JS et al. (2005) Science "Glycolipids as receptors for Bacillus thuringiensis crystal toxin."

Haslam SM, Morris H, Garczynski SF, Griffitts JS, Adang MJ, Cremer PS, Aroian RV, Yang T, Mulloy B, Dell A

[Science, 2005]

The development of pest resistance threatens the effectiveness of Bacillus thuringiensis (Bt) toxins used in transgenic and organic farming. Here, we demonstrate that (i) the major mechanism for Bt toxin resistance in Caenorhabditis elegans entails a loss of glycolipid carbohydrates; (ii) Bt toxin directly and specifically binds glycolipids; and (iii) this binding is carbohydrate-dependent and relevant for toxin action in vivo. These carbohydrates contain the arthroseries core conserved in insects and nematodes but lacking in vertebrates. We present evidence that insect glycolipids are also receptors for Bt toxin.

Griffitts JS et al. (2001) Science "Bt toxin resistance from loss of a putative carbohydrate-modifying enzyme."

Whitacre JL, Aroian RV, Stevens DE, Griffitts JS

[Science, 2001]

The development of resistance is the main threat to the long-term use of toxins from Bacillus thuringiensis (Bt) in transgenic plants. Here we report the cloning of a Bt toxin resistance gene, Caenorhabditis elegans bre-5, which encodes a putative beta -1,3-galactosyltransferase. Lack of bre-5 in the intestine led to resistance to the Bt toxin Cry5B. Wild-type but not bre-5 mutant animals were found to uptake toxin into their gut cells, consistent with bre-5 mutants lacking toxin-binding sites on their apical gut. bre-5 mutants displayed resistance to Cry14A, a Bt toxin lethal to both nematodes and insects; this indicates that resistance by loss of carbohydrate modification is relevant to multiple Bt toxins.

Ammons DR et al. (2009) Curr Microbiol "An investigation of bacillus thuringiensis in rectal-collected fecal samples of cows."

Rampersad JN, Granados JC, Reyna A, Ammons DR, Samlal MS

[Curr Microbiol, 2009]

In order to better understand the range and role of Bacillus thuringiensis (Bt) and its toxins in nature, we have undertaken a study of Bt taken directly from the rectum of 117 cows from 37 farms on the Caribbean island of Trinidad. Thirty-seven fecal samples (32%) were found to contain at least one Bt. Generally only one or two isolates with a particular crystal morphology were isolated from any one sample, however, a few samples contained more, up to 11 isolates, suggesting post-ingestion amplification. Bioassays using larvae of Musca domestica, Caenorhabditis elegans and Tetrahymena pyriformis showed no observable toxicity in gross bioassays. Very small dot-like parasporal bodies, not generally characteristic of Bt, were isolated from 44% of the samples, which in many instances appeared unstable and whose relation to Bt Cry protein-containing parasporal bodies is unknown. In conclusion, we find little evidence for a host adapted strain of Bt in the cows examined, nor toxicity to organisms that might logically be associated with either the cow or its feces. The presence of a large number of isolates containing small dot-like parasporal bodies, possibly either poly-beta-hydroxybutyrate storage bodies or Cry proteins, was unexpected and merits further investigation.

Wan L et al. (2019) Environ Microbiol "Bacillus thuringiensis targets the host intestinal epithelial junctions for successful infection of Caenorhabditis elegans."

Sun M, Wan L, Bravo A, Lin J, Soberon M, Du H, Peng D

[Environ Microbiol, 2019]

Pathogenic bacteria use different strategies to infect their hosts, including the simultaneous production of pore forming toxins and several virulence factors that may synergize their pathogenic effects. However, how the pathogenic bacteria are able to break out the host intestinal barrier is poorly understood. The infectious cycle of Bacillus thuringiensis (Bt) bacterium in Caenorhabditis elegans is a powerful model system to study the early stages of the infection process. Bt produces Cry pore-forming toxins during the sporulation phase that are key virulence factors involved in its pathogenesis. In this study, we show that Bt disrupts the intestinal epithelial junctions of C. elegans at early stages of infection allowing Bt bacterium to complete its life cycle in the worm. We further confirmed that the vegetative Bt cells trigger a quorum sensing response that is activated by PlcR regulator, resulting in production of different virulence factors, such as the metalloproteinases ColB and Bmp1, that besides Cry toxins are necessary to disrupt the nematode epithelial junctions causing efficient bacterial host infection and death of the nematode. Our work provides new insights into the pathogenesis of Bt, and highlights the importance of breaking down host epithelial junctions for a successful infection. A similar mechanism could be used by other pathogen-host interactions since epithelial junctions are conserved structures from insects to mammals. This article is protected by copyright. All rights reserved.

Guo X et al. (1995) J Parasitol "Hemocyte alterations during melanotic encapsulation of Brugia malayi in the mosquito Armigeres subalbatus."

Christensen BM, Guo X, Zhao X, Beerntsen BT

[J Parasitol, 1995]

The involvement of hemocytes in melanotic encapsulation reactions against Brugia malayi was assessed in Armigeres subalbatus. Hemocyte populations, epitope changes, phenol oxidase (PO) activity, and the presence of an 84-kDa polypeptide were investigated in mosquitoes exposed to a B. malayi-infective bloodmeal (= immune-activated), in mosquitoes given a noninfective bloodmeal (= controls), in nonbloodfed mosquitoes (= naive), or in some combination of these. Total hemocyte populations in immune-activated mosquitoes significantly decreased at 24 hr postbloodmeal (PB) as compared with controls. At 48 and 72 hr PB, hemocyte population levels in immune-activated mosquitoes increased to control levels. Epitope changes, as indicated by wheat germ agglutinin (WGA) binding, also were observed. There was a significant increase in the percentage of hemocytes binding WGA in immune-activated mosquitoes at 24 hr PB as compared with controls. Furthermore, the activity of hemocyte PO, an enzyme involved in the melanotic encapsulation pathway, was significantly elevated at 12 hr PB in immune-activated mosquitoes as compared with controls. Analysis for the presence of an 84-kDa polypeptide in A. subalbatus indicates that a 2.0-kb message in total RNA hybridized to D6.12, an Aedes aegypti cDNA encoding an 84-kDa polypeptide that is associated with melanotic encapsulation responses. The hybridization of D6.12 to RNA was not greater in immune-activated as compared to control A. subalbatus, as has been observed in A. aegypti. Results indicate that these hemocyte changes correspond in time with the melanotic encapsulation reactions of A. subalbatus against filarial worms.

Zarate-Potes A et al. (2021) Dev Comp Immunol "The effects of nested miRNAs and their host genes on immune defense against Bacillus thuringiensis infection in Caenorhabditis elegans."

Nakad R, Schulenburg H, Dierking K, Haase D, Rosenstiel P, Andresen B, Yang W, Zarate-Potes A

[Dev Comp Immunol, 2021]

microRNAs (miRNAs) are small non-coding RNA-molecules that influence translation by binding to the target gene mRNA. Many miRNAs are found in nested arrangements within larger protein-coding host genes. miRNAs and host genes in a nested arrangement are often transcribed simultaneously, which may indicate that both have similar functions. miRNAs have been implicated in regulating defense responses against pathogen infection in C. elegans and in mammals. Here, we asked if miRNAs in nested arrangements and their host genes are involved in the C. elegans response against infection with Bacillus thuringiensis (Bt). We performed miRNA sequencing and subsequently focused on four nested miRNA-host gene arrangements for a functional genetic analysis. We identified mir-58.1 and mir-2 as negative regulators of C. elegans resistance to Bt infection. However, we did not find any miRNA/host gene pair in which both contribute to defense against Bt.

Hoss S et al. (2008) Ecotoxicol Environ Saf "Effects of transgenic corn and Cry1Ab protein on the nematode, Caenorhabditis elegans."

Nguyen HT, Arndt M, Tebbe CC, Hoss S, Baumgarte S, Jehle JA

[Ecotoxicol Environ Saf, 2008]

The effects of the insecticidal Cry1Ab protein from Bacillus thuringiensis (Bt) on the nematode, Caenorhabditis elegans, were studied with soil from experimental fields cultivated with transgenic Bt corn (MON810) and with trypsinized Cry1Ab protein expressed in Escherichia coli. The content of Cry1Ab protein was above the detection limit of an ELISA test in only half of the soil samples obtained from transgenic plots, ranging from 0.19 to 1.31ngg(-1) dry weight. In a laboratory bioassay, C. elegans was exposed to rhizosphere and bulk soil from fields with isogenic or transgenic corn or to solutions of Cry1Ab protein (0, 24, 41, 63, 118, and 200mgl(-1)) over a period of 96h, with growth and reproduction serving as the test parameters. Nematode reproduction and growth were significantly reduced in rhizosphere and bulk soil of Bt corn compared with soil from isogenic corn and were significantly correlated with concentrations of the Cry1Ab protein in the soil samples. Moreover, the toxicity of pure Cry1Ab protein to the reproduction and growth of C. elegans was concentration-dependent. As significant inhibition occurred at relatively high concentrations of the Cry1Ab protein (41mgl(-1)), the effects of the soil samples from Bt corn could not be assigned directly to the toxicity of the Cry1Ab protein. The results demonstrate that bioassays with the nematode, C. elegans, provide a promising tool for monitoring the potential effects of Bt toxins in aqueous medium and soils.