Over the summer, an article was published which featured a handful of researchers from across the US and research spanning a decade on the bacterial communities associated with invasive ants and nematodes in Maine. At the time, we were invited to also contribute a “Backstory” article to the scientific journal iScience which described the journey and the ideas.
That story authored by myself and Ellie Groden (senior researcher on the journal article) has just been published, and can be found here. I’d like to thank Dr. Sheba Agarwal, who was the editor on the paper, helped us develop our Backstory, and also spoke to me about this and other work as a guest on the WeTalkScience podcast.
Next week kicks off the live events, including with question + answer, discussions, and special sessions being held in real time, for the Ecological Society of America’s annual conference, which is being held virtually this year. Prerecorded presentations are already available on demand.
Can a necromenic nematode serve as a biological Trojan horse for an invasive ant?
Session 1-PS7: Vital Connections in Ecology: Breakthroughs in Understanding Species Interactions
Poster and narration available on demand.
Live discussion: Monday, August 2, 2021, 9:30 AM – 10:30 AM Pacific Time
Background/Question/Methods The invasive European fire ant (Myrmica rubra) threatens native ant species and human health along the coast of Maine, United States. M. rubra mortality has been associated with infection by Pristionchus entomophagus, a necromenic nematode that is hypothesized to transfer pathogenic bacteria acquired from the environment to ant colonies. To investigate this hypothesis, we conducted a series of experiments on nematode-infected ants collected from Mount Desert Island. First, we isolated bacteria cultured from nematodes emerging from M. rubra cadavers and assessed the ability of the nematodes to acquire and transfer environmental bacteria to Galleria mellonella waxworm larvae. Second, we identified bacteria which were potentially transferred from nematodes to infected ant nests on MDI using bacterial community similarity and sequence tracking methods.
Results/Conclusions Multiple bacterial species, including Paenibacillus spp., were found in the nematodes’ digestive tract. Serratia marcescens, Serratia nematodiphila, and Pseudomonas fluorescens were collected from the hemolymph of nematode-infected G. mellonella larvae. Variability was observed in insect virulence in relation to the site origin of the nematodes. In vitro assays confirmed uptake of red fluorescence protein (RFP)-labeled Pseudomonas aeruginosa strain PA14 by nematodes. Bacteria were highly concentrated in the digestive tract of adult nematodes, some bacteria were observed in the digestive tract of juveniles with a more significant amount on their cuticle, and none on the cuticle of adults. RFP-labeled P. aeruginosa were not observed in hemolymph of G. mellonella larvae, indicating an apparent lack of bacterial transfer from juvenile nematodes to the insects despite larval mortality.
Host species was the primary factor affecting bacterial community profiles. Spiroplasma sp. and Serratia marcescens sequences were shared across ants, nematodes, and nematode-exposed G. mellonella larvae. Alternative to the idea of transferring bacteria from environment to host, we considered whether nematode-exposure might disorder or depauperate the endobiotic community of an insect host. While total bacterial diversity was not statistically lower in nematode-exposed G. mellonella larvae when compared to controls, 16 bacterial sequence variants were less abundant in nematode-exposed larvae, while three were increased, including Serratia, Pseudomonas, and Proteus. This study suggests that transfer of bacteria from nematodes to ants is feasible, although largely serendipitous, and may contribute to ant mortality in Maine. Hypothetically, the use of an engineered biological control, such as nematodes carrying specifically-seeded bacterial species, may be effective, especially if the pathogenic bacteria are naturally found in soil ecosystems and represent a low risk for biosafety control.
Poster Citation: Hotopp*, A., Silverbrand, S., Ishaq, S.L., Dumont, J., Michaud, A., MacRae, J., Stock, S.P., Groden, E. “Can a necromenic nematode serve as a biological Trojan horse for an invasive ant?” Ecological Society of America 2021. (virtual). Aug 2-6, 2021. (poster)
Ishaq, S.L., A. Hotopp2, S. Silverbrand2, J.E. Dumont, A. Michaud, J. MacRae, S. P. Stock, E. Groden. 2021. Assessment of pathogenic bacteria transfer from Pristionchus entomophagus (Nematoda: Diplogasteridae) to the invasive fire ant (Myrmica rubra) and its potential role in colony mortality in coastal Maine. iScience 24(6):102663. Article.
Talk #93066, “The effect of simulated warming ocean temperatures on the bacterial communities on the shells of healthy and epizootic shell diseased American Lobster (Homarus americanus)”
COS 87: Climate Change: Communities 1 Recorded talk available on demand.
The American lobster, Homarus americanus, is a vital species for the fishing industry along the North Atlantic coast of North America. However, populations in Southern New England have declined, most likely due to increasing ocean temperatures and prevalence of emerging disease. Our previous work suggested that temperature may not be the sole cause for epizootic shell disease (ESD). Here, we examined the shell bacterial communities and progression of ESD in non-shell diseased and diseased adult female lobsters under three simulated seasonal temperature cycles for a year.
Fifty-seven female lobsters were wild-caught from Maine’s management zones F and G, and were assessed for shell disease progression on a scale of 0 (no observable signs) to 3 (visible disease on >50% of the shell surface). ESD-negative lobsters (apparently healthy) and ESD-positive (diseased) lobsters were randomly dispersed into 3 systems, and within each system, healthy and diseased lobsters were placed into separate tanks. These systems were maintained at three temperature ranges comparable to the average seasonal ocean temperatures for Southern New England (SNE), Southern Maine (SME), and Northern Maine (NME) regions. Samples were collected at three timepoints, a baseline “summer” temperature where all tanks were the same temperature, a winter temperature four months later, and a summer temperature 10 months after that.
A total of 131 experimental samples, plus 10 controls, passed PCR amplification, amplicon quantification and purification, Illumina MiSeq ver. 4 sequencing, and quality-control filtering. Sequences were processed using the R software platform, using DADA2, phyloseq, vegan, and assorted other packages.
Results and conclusions
The bacterial richness on lobster shells at the baseline timepoint, when lobsters were wild-caught, was higher than the winter time point, 4 months later, or the summer time point, 10 months later, for the same lobsters after having been kept in tanks, regardless of their temperature or shell disease status. Similarly, the bacterial community membership (unweighted Jaccard similarity) was similar for all samples at baseline, but diverged for later time points.
Tank temperature significantly affected microbial community membership (unweighted Jaccard similarity), as well as the abundance of those community members (weighted Bray-Curtis dissimilarity).
Contrary to our expectations, ESD shell disease index did not progress over time or in warmer conditions, and we hypothesized that frequent tank water changes and shell moltings may have reduced the microbial load. Preliminary results indicate that shell stage and shell disease index were positively associated with increased bacterial richness on lobster shells.
Citation: Ishaq*, S.L., Lee, G., MacRae, J., Hamlin, H., Bouchard, D. “The effect of simulated warming ocean temperatures on the bacterial communities on the shells of healthy and epizootic shell diseased American Lobster (Homarus americanus).” Ecological Society of America 2021. (virtual). Aug 2-6, 2021. (accepted talk)
SS 17: “Microbiomes and Social Equity” (19205)
Prerecorded content available on demand.
Live discussion: Thursday, August 5th, 2021, 9:30 AM – 10:30 AM Pacific Time
Microbiomes — environmental, human and other organismal symbionts — are increasingly seen as critical physiological, developmental and ecological mediators within and among living things, and between the latter and our abiotic environments. Therefore, it is no surprise that microbial communities may be altered, depleted or disrupted by social and economic determinants. Social inequality entails concrete alterations and differentiation of microbial communities among social groups, by way of such factors as nutritional access, environmental pollutants or green space availability, often to the detriment of human and ecosystem health. This special session will be organized as a panel discussion with break-out groups in order to provide participants the opportunity to discuss the ways in which social inequity interacts with microbiomes, and how we might intervene as scientists and communities to promote favorable microbiomes while advancing social equality. We hope to generate research questions and actionable items.
Panel speakers: Michael Friedman, Naupaka Zimmerman, Justin Stewart, Monica Trujillo, Sue Ishaq, Sierra Jech, Jennifer Bhatnagar, and Ariangela Kozik ESA meeting program: https://www.esa.org/longbeach/
Citation: The Microbes and Social Equity Working group, “Special Session 17: “Microbiomes and Social Equity” (19205).”, Ecological Society of America 2021. (virtual). Aug 5, 2021.
A few weeks ago, I sat down with Sheba A-J, one of the producers of the WeTalkScience podcast, to talk about one of my recent publications in the research journal iScience, at which Sheba is also an editor. Listen to find out how lobsters are like humans, how I got involved on a project working with ants and nematodes, and how you can help make science a more welcoming place.
The full publication is:
Ishaq, S.L., A. Hotopp, S. Silverbrand, J.E. Dumont, A. Michaud, J. MacRae, S. P. Stock, E. Groden. 2021. Bacterial transfer from Pristionchus entomophagus nematodes to the invasive ant Myrmica rubra and the potential for colony mortality in coastal Maine. iScience 24(6):102663. Article.
A collaborative paper on bacterial transfer in insects and the possible ecological impacts of that in the wild has been published in iScience! This work began a decade ago in the labs of Dr. Ellie Groden, recently retired Professor of Entomology in the School of Biology and Ecology at the University of Maine, and later Dr. Patricia Stock, a Professor in the School of Animal and Comparative Biomedical Sciences at the University of Arizona, who were investigating colony collapse of European fire ants (Myrmica rubra) which are invasive to Maine. The ants have a nasty bite, and can dramatically disturb the local plant and insect wildlife in coastal Maine.
When these invasive ant colonies collapsed, Drs. Groden and Stock wanted to find out why, as a possible means of developing a biological control strategy. It was thought that particular nematodes would ingest soil bacteria, and transfer it to ants once the worms invaded ant tissues to complete parts of their life cycle. This particular worm infection doesn’t kill the ants, but perhaps the soil bacteria were. Ants were collected from different colony sites, and investigations on the nematode worms inhabiting the ants were conducted.
Most of the work for this project was completed several years ago, with the exception of DNA sequencing data from a bacterial transfer experiment. I was added to the project by my collaborator at UMaine, Dr. Jean MacRae, an Associate Professor in the Department of Civil and Environmental Engineering who introduced me to the research team and shared the 16S rRNA dataset to use in my AVS 590 data analysis class in spring 2020. That semester was when the pandemic hit, and forced the course to move to remote-only instruction in March. UMaine graduate students Alice Hotopp and Sam Silverbrand were taking the class and learning 16S analysis on this dataset, and I mentored them through the analysis all the way to manuscript writing despite the incredible challenges that spring threw our way.
At the completion of the course, we shared the draft manuscript with the rest of the research team, who mentioned that several undergraduate honor’s theses had been written about the earlier experiment, but never published in a scientific journal. The team spent summer 2020 combining the three papers into one massive draft. The pandemic slowed down manuscript review, understandably, but I’m pleased to say that it was accepted for publication! In addition, this collaboration has led to further collaborations in the Ishaq Lab, several presentations (listed below), and is Sam’s first scientific publication, congrats Sam!!
Alice Hotopp, A., Samantha Silverbrand, Suzanne L. Ishaq, Jean MacRae, S. Patricia Stock, Eleanor Groden. “Can a necromenic nematode serve as a biological Trojan horse for an invasive ant?” Ecological Society of America 2021 (virtual). Aug 2-6, 2021 (accepted poster).
Ishaq*, S.L., Hotopp, A., Silverbrand, S., MacRae, J., Stock, S.P., Groden, E. “Can a necromenic nematode serve as a biological Trojan horse for an invasive ant?” Entomological Society of America 2020 (virtual). Nov 15-25, 2020. (invited talk)
The necromenic nematode Pristionchus entomophagus has been frequently found in nests of the invasive European ant Myrmica rubra in coastal Maine, United States, and may contribute to ant mortality and collapse of colonies by transferring environmental bacteria. Paenibacillus and several other bacterial species were found in the digestive tracts of nematodes harvested from collapsed ant colonies. Serratia marcescens, Serratia nematodiphila, and Pseudomonas fluorescens were collected from the hemolymph of nematode-infected wax moth (Galleria mellonella) larvae.
Virulence against waxworms varied by site of origin of the nematodes. In adult nematodes, bacteria were highly concentrated in the digestive tract with none observed on the cuticle. In contrast juveniles had more on the cuticle than in the digestive tract. . Host species was the primary factor affecting bacterial community profiles, but Spiroplasma sp. and Serratia marcescens sequences were shared across ants, nematodes, and nematode-exposed G. mellonella larvae.