I gave a lecture on animal-fungal symbionts and parasites this week so was doing more reading of recent literature on insect-fungi associations. A couple of quick notes worth sharing.
Ophiocordyceps unilateralis was the parasite of the day last week and includes a description of an interesting recent paper looking at the consistency of the symptoms of zombie ants. The article also mentions Carl Zimmer’s post on the same paper in more detail.
You of course have seen the very cool electronic/online Cordyceps monograph at cordyceps.us from Joey Spatafora’s lab?
The genome of Cordyceps militaris was sequenced by researchers at the Chinese Academy of Sciences. They find a reduced copy numbers of many gene families suggesting to the authors that the specialized ecology of the fungus may have limited the need for expanded gene families. The do find expanded copy numbers of metalloproteases – a finding we have also seen in human and amphibian associated pathogens as well as by the authors who looked at the insect associated fungus Metarhizium. There is also a reduction in cutinases and genes related to degrading plant cell walls similar to findings in the human associated pathogens Coccidioides suggesting similar genomic routes to specializing on an animal host from a generalist. They also found that this fungus is heterothallic based on genomic identification of the MAT1-1 locus. There are several more interesting findings in the paper including expression profiling of fruiting body via RNA-Seq.
Zheng, P., Xia, Y., Xiao, G., Xiong, C., Hu, X., Zhang, S., Zheng, H., Huang, Y., Zhou, Y., Wang, S., Zhao, G., Liu, X., St Leger, R., & Wang, C. (2011). Genome sequence of the insect pathogenic fungus Cordyceps militaris, a valued traditional Chinese medicine Genome Biology, 12 (11) DOI: 10.1186/gb-2011-12-11-r116
A critical part of understanding and documenting the diversity is formal descriptions of species and their relatives. This can be a laborious task and is usually captured in the form of a monograph of a species where a group of species are described in careful detail along with the phylogenetic relationships of them. This has served as the basis for documentation of the the natural history and morphological descriptions of species. The information is typically presented in the form of a book that goes to a library or your shelf which can be pulled down and poured over when trying to determine traits for a group of organisms. Books are great but sharing images and the
Ryan Kepler, a PhD student at Oregon State, is writing a monograph about the ever so cool Cordyceps fungi which have intimate and quite manipulative relationship with insects. However, he’s doing it as an electronic monograph that he is publishing on the web. This is a great way to share this technical and visual information. By publishing it online he is making it searchable and so that it can be a living document that can be updated over time. He’s also willing to publish it as he goes along so the current version is a starting point, but will continue to mature as he completes his PhD thesis work and has input from other experts in the field. I really like that the is publishing it early on and truly embracing an open science approach to presenting his descriptions of the species and their relationships. This is akin to other efforts putting information about species on the web, from the Encyclopedia of Life to Mushroom observer, but I really like that this is a site dedicated to capturing the expert level information that Ryan is gathering as part of this thesis in a searchable and interactive form.
Cordyceps are an interesting group of fungi not only because of their insect association, but their variety of colors and morphologies. The ability to manipulate their insect hosts also suggests a wide variety of secondary metabolites are probably produced by these fungi to enable them to change behavior of infected individuals.
Will be great to see this resource mature and also additional monographs and species descriptions to embrace an online and freely available form. I suspect there could be a (tiny) market for better web software here for making this easier so that one doesn’t have to be or have an expert web development team to deploy these for individual projects.
Another result from the analysis of the recently published genome of the pea aphid, Acyrthosiphon pisum. Nancy Moran and Tyler Jarvik present a study of the origin of the carotenoid production gene in pea aphid. Animals typically cannot make carotenoids so they sought to discover how this is possible. They find that it is derived from a horizontal gene transfer event of a fungal gene into the aphid lineage. This gene is responsible for the red-green color polymorphism in the aphid. It appears the gene is derived from a ‘zygomycete’ or relative in the early branching lineage of the fungi. One gene, a carotenoid desaturase, is encoded in a 30kb genomic region that is missing in green aphids but present in the red morphs. The region is apparently maintained in the population by frequency dependent selection since each color has an advantage or disadvantage for evading detection by predators in different environments.
The reports of eukaryotic HGT event from fungi to animals is quite rare so this finding is surprising in that sense, but the authors argue that the important ecological role of carotenoids suggest we might see even more examples if we look harder.
Moran, N., & Jarvik, T. (2010). Lateral Transfer of Genes from Fungi Underlies Carotenoid Production in Aphids Science, 328 (5978), 624-627 DOI: 10.1126/science.1187113
Nature News has a cool story about peering into amber with X-rays from the European Synchrotron Radiation Facility. There are some great images of wasps and spiders that could be gleaned from the otherwise opaque amber. Could one also determine fungal spore characteristics from this sort of scan?
An early access to article in Science A Metagenomic Survey of Microbes in Honey Bee Colony Collapse Disorder (direct link since DOI is not updated yet) using the current favorite buzzword, metagenomics, of course, describes some early work to try and discover what is killing the honeybees. It is early access and non-free and ScienceExpress is not part of our subscription here so I’ve not actually had a chance to read it yet, but the gist of the reporting about it suggest that a virus is to blame. This is in line with what Joe DeRisi and collaborators found using their Virus chip based on some news reports earlier this year, but no scientific article yet to follow this up.
Some links to today’s SFChronicle article and an article “Stung” from the New Yorker in August that alluded to this Science article.
I read this blurb in the New Scientist about a PNAS paper (subscription required for next 6 months) on how hive beetles (Aethina tumida) are able to infest bee hives by throwing off the bees because they are producing isopentyl acetate which is thought to be produced and used by bees to signal an alarm. So the increased levels of the pheromone disorients the bees allowing beetles to continue infecting. European bees appear to be susceptible to this attack while the African bees have apparently evolved to better handle the beetle infestation. I’m not clear if the African bees have a different behavior or if they have different biochemical pathways/receptors to not be fooled by the cheap perfume of the invaders.
The fungus part here is that the beetles are carrying a hemiascomycete yeast, Kodamaea ohmeri in the Saccharomyces clade (see Suh and Blackwell 2005 for more details), which produces the isopentyl acetate pheromone. So it is a sort of auto-immune hive reaction where the defense mechanism is being short-circuited and harming the host.
Continue reading Would a Beetle by another name smell as sweet?
I don’t know if you’ve heard, but bee colonies are disappearing! Colony collapse disorder, as this phenomenon is better known, worries bee-keepers, agriculturalists and insect admirers all over: over 25% of the commerical bee colonies have disappeared since last fall. Normally, when a commerical hive collapses, honey is left behind in the box and wild bees set up shop on top of this free resource. But it seems that wild bees are also suffering, as honey filled boxes remain bee-less.
Researchers are scrambling to determine the cause of this bee die-off. Given the agricultural implications of losing one of nature’s best pollinators, time is of the essence. All sorts of hypotheses have been suggested, from pesticides or pathogens to solar flares and cell phones, but little evidence has been accumulated (mostly due to the fact that bee bodies are rarely found).
Fortunately, a recent breakthrough occured at UCSF. Joe DiRisi’s group found, in collaboration with other researchers, that Nosema ceranae (a microsporidian) had invaded several dead bees that had been found in the wild. There are several bee pathogens in the fungi (e.g. Ascosphera apis, whose genome was recently sequenced), but the discovery of Nosema infection is notable given that Nosema apis was the cause of widespread colony collapse disorder in Spain during the mid-nineties.
So is this pathogen the cause of the widespread colony die off? The jury is still out. But this represents some of the best evidence to date that fungi may be playing a role in this unfortunate event.
Not fungal, but cool science nonetheless (plus, ants are important in some fungal symbioses). Walter R. Tschinkel uses plaster to study ant nests (particularly the Florida harvester ant, Pogonomyrmex badius) and his recent article in Bioone provides us an interesting insight into any colony morphology. Check it out.
The Baylor sequencing center has published the genome of two honey bee pathogens. Recently Baylor and collaborators published a slew of honey bee genome papers and it is great that they have also chosen to follow up on the parasites as well.
The group published the genomes of the bacteria pathogen Paenibacillus larvae and fungal pathogen Ascosphaera apis. A. apis is in the Onygenales clade which also includes the fungal human pathogens Coccidioides, Histoplasma, and Blastomyces.
Currently the genome annotation is limited to the bacterial genome where many ab initio gene prediction programs exist and no annotation is provided for A. api. We should be able to apply gene prediction parameters trained from other Onygenales fungi to get a resonable annotation. Study of this pathogenic genome may also provide insight into the evolution of this clade of fungi which contains most of the primary fungal pathogens of humans.
Ants, fungi, and bacteria
I have to admit that I am fascinated by co-evolution of symbiotic and mutalistic systems. A review by Richard Robinson gives an overview. A great example is the mutalism between ants and fungi where the ants cultivate the fungi for food. There are more layers to the relationship as a fungal parasite (Escovopsis) attacks the cultivated fungi, and a bacteria. Several researchers have studied the coevolution of these studies including Ulrich Mueller and Cameron Currie. Currie and Mueller have published several great studies describing the patterns of coevolution and the nature of the cooperation.
Continue reading Tripartate symbioses with fungi