Bee-Killing Parasite Genome Sequenced
Honey bee colonies are in decline in many parts of the world, in part due to pressures from a diverse assemblage of parasites and pathogens. Scientists have sequenced the genome of a parasite that can kill honey bees. Nosema ceranae is one of many pathogens suspected of contributing to the current bee population decline, termed colony collapse disorder (CCD). In 2006, CCD began devastating commercial beekeeping operations, with some beekeepers reporting losses of up to 90 percent, according to the USDA. Researchers believe CCD may be the result of a combination of pathogens, parasites and stress factors, but the cause remains elusive. At stake are honey bees that play a valuable part in a $15 billion industry of crop farming in the United States.
The microsporidian Nosema is a fungus-related microbe that produces spores that bees consume when they forage. Infection spreads from their digestive tract to other tissues. Within weeks, colonies are either wiped out or lose much of their strength. Nosema apis was the leading cause of microsporidia infections among domestic bee colonies until recently when N. ceranae jumped from Asian honey bees to the European honey bees used commercially in the United States. Sequencing the genome should help scientists trace the parasite’s migration patterns, determine how it became dominant, and help resolve the spread of infection by enabling the development of diagnostic tests and treatments.
N. ceranae has an extremely reduced and AT-biased genome, yet one with substantial numbers of repetitive elements. The sequence identifies novel genes that appear to be conserved among microsporidia but undetected outside this phylum, which are of special interest as potential virulence factors for these obligate pathogens. A previously unrecognized motif is found upstream of many start codons and likely plays a role in gene regulation across the microsporidia. These and other comparisons provide insight into the architecture, regulation, and evolution of microsporidian genomes, and provide the first genetic tools for understanding how this pathogen interacts with honey bee hosts.
Genomic Analyses of the Microsporidian Nosema ceranae, an Emergent Pathogen of Honey Bees. PLoS Pathog 5(6): e1000466. doi:10.1371/journal.ppat.1000466
Recent steep declines in honey bee health have severely impacted the beekeeping industry, presenting new risks for agricultural commodities that depend on insect pollination. Honey bee declines could reflect increased pressures from parasites and pathogens. The incidence of the microsporidian pathogen Nosema ceranae has increased significantly in the past decade. Here we present a draft assembly (7.86 MB) of the N. ceranae genome derived from pyrosequence data, including initial gene models and genomic comparisons with other members of this highly derived fungal lineage. N. ceranae has a strongly AT-biased genome (74% A+T) and a diversity of repetitive elements, complicating the assembly. Of 2,614 predicted protein-coding sequences, we conservatively estimate that 1,366 have homologs in the microsporidian Encephalitozoon cuniculi, the most closely related published genome sequence. We identify genes conserved among microsporidia that lack clear homology outside this group, which are of special interest as potential virulence factors in this group of obligate parasites. A substantial fraction of the diminutive N. ceranae proteome consists of novel and transposable element proteins. For a majority of well-supported gene models, a conserved sense-strand motif can be found within 15 bases upstream of the start codon; a previously uncharacterized version of this motif is also present in E. cuniculi. These comparisons provide insight into the architecture, regulation, and evolution of microsporidian genomes, and will drive investigations into honey bee–Nosema interactions.
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Tags: bees, Biology, Emerging disease, Microbiology, Nosema, Science
This is a problem I’ve been following for some time, and hadn’t heard any recent updates. Thank you so much for writing about this! I live in Morocco, and some people here told me that if the colonies collapsed that there are still enough other “natural” pollinators around (wild bees, butterflies—which I wasn’t even aware were pollinators) that they didn’t think the crops would collapse…..I have my doubts about this, though! Has this disorder invaded Africa yet?