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.
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.
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.
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.