MicrobiologyBytes

I’ve written here before about how colony-collapse disorder (CCD) is affecting bees worldwide, but this new article from Trends in Microbiology is a good insight into the current state of knowledge:

Bees brought to their knees: microbes affecting honey bee health. Trends Microbiol. Oct 25 2011
The biology and health of the honey bee Apis mellifera has been of interest to human societies for centuries. Research on honey bee health is surging, in part due to new tools and the arrival of colony-collapse disorder (CCD), an unsolved decline in bees from parts of the United States, Europe, and Asia. Although a clear understanding of what causes CCD has yet to emerge, these efforts have led to new microbial discoveries and avenues to improve our understanding of bees and the challenges they face. Here we review the known honey bee microbes and highlight areas of both active and lagging research. Detailed studies of honey bee–pathogen dynamics will help efforts to keep this important pollinator healthy and will give general insights into both beneficial and harmful microbes confronting insect colonies.

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There are numerous threats facing honey bee populations and the recent losses of honey bee colonies in the United States, Canada, and Europe is alarming. In the U.S., annual honey bee colony losses increased from 17–20% to 32% during the winter of 2006/07 with some operations losing 90% of their hives. Average annual losses have remained high, averaging 32% from 2007–2010. One factor contributing to increased losses is Colony Collapse Disorder (CCD), an unexplained loss of honey bee colonies fitting a defined set of criteria. While factors such as pesticide exposure, transportation stress, genetic diversity, and nutrition affect colony health, the most significant CCD-associated variable characterized to date is increased pathogen incidence. Although greater pathogen incidence correlates with CCD, the cause is unknown in part due to insufficient knowledge of the pathogenic and commensal organisms associated with honey bees.

To gain a more complete understanding of the spectrum of infectious agents and potential threats found in commercially managed migratory honey bee colonies, researchers conducted a 10-month investigation. Analysis incorporated a suite of molecular tools (custom microarray, polymerase chain reaction (PCR), quantitative PCR (qPCR) and deep sequencing) enabling rapid detection of the presence (or absence) of all previously identified honey bee pathogens as well as facilitating the detection of novel pathogens. This study provides a comprehensive temporal characterization of honey bee pathogens and offers a baseline for understanding current and emerging threats to this critical component of U.S. agriculture.

Discovery and characterization of four new viruses will facilitate future monitoring of bee colones. Temporal characterization of these and other microbes offers a more complete view of the possible microbe-microbe and microbe-environment interactions. Further studies examining any subtle or combinatorial effects of these novel microbes are required to understand their role in colony health.

Temporal Analysis of the Honey Bee Microbiome Reveals Four Novel Viruses and Seasonal Prevalence of Known Viruses, Nosema, and Crithidia. (2011) PLoS ONE 6(6): e20656. doi:10.1371/journal.pone.0020656
Honey bees (Apis mellifera) play a critical role in global food production as pollinators of numerous crops. Recently, honey bee populations in the United States, Canada, and Europe have suffered an unexplained increase in annual losses due to a phenomenon known as Colony Collapse Disorder (CCD). Epidemiological analysis of CCD is confounded by a relative dearth of bee pathogen field studies. To identify what constitutes an abnormal pathophysiological condition in a honey bee colony, it is critical to have characterized the spectrum of exogenous infectious agents in healthy hives over time. We conducted a prospective study of a large scale migratory bee keeping operation using high-frequency sampling paired with comprehensive molecular detection methods, including a custom microarray, qPCR, and ultra deep sequencing. We established seasonal incidence and abundance of known viruses, Nosema sp., Crithidia mellificae, and bacteria. Ultra deep sequence analysis further identified four novel RNA viruses, two of which were the most abundant observed components of the honey bee microbiome (~10^11 viruses per honey bee). Our results demonstrate episodic viral incidence and distinct pathogen patterns between summer and winter time-points. Peak infection of common honey bee viruses and Nosema occurred in the summer, whereas levels of the trypanosomatid Crithidia mellificae and Lake Sinai virus 2, a novel virus, peaked in January.

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Bats, which are ‘keystone species’ in many ecosystems, play notable roles in plant pollination, forest regeneration and control of insect populations. Bats are important to human health as they are reservoirs or carriers for rabies and other viruses, parasites, and pathogenic fungi. Hibernation is believed to be an important adaptation in bats that may contribute to their exceptional longevity. The common little brown bat (Myotis lucifugus) hibernates, along with the endangered Indiana bat (Myotis sodalis), in many hibernacula in the Northeastern United States, including caves and mines in upstate New York. Hibernating bats can suffer significant mortality due to adverse environmental conditions such as freezing or flooding, as well as human activities including visitation and pesticide applications. No mass mortality was reported until recently from bat sites that had been surveyed for almost three decades by the New York State Department of Environmental Conservation. Recently, however little brown bats have been found to be dying in large numbers at many hibernation sites in upstate New York. This problem has spread to other States in the Northeastern USA.

Morphological and Molecular Characterizations of Psychrophilic Fungus Geomyces destructans from New York Bats with White Nose Syndrome (WNS). PLoS ONE 5(5): e10783. doi:10.1371/journal.pone.0010783
Massive die-offs of little brown bats (Myotis lucifugus) have been occurring since 2006 in hibernation sites around Albany, New York, and this problem has spread to other States in the Northeastern United States. White cottony fungal growth is seen on the snouts of affected animals, a prominent sign of White Nose Syndrome (WNS). A previous report described the involvement of the fungus Geomyces destructans in WNS, but an identical fungus was recently isolated in France from a bat that was evidently healthy. The fungus has been recovered sparsely despite plentiful availability of afflicted animals.
We have investigated 100 bat and environmental samples from eight affected sites in 2008. Our findings provide strong evidence for an etiologic role of G. destructans in bat WNS. (i) Direct smears from bat snouts, Periodic Acid Schiff-stained tissue sections from infected tissues, and scanning electron micrographs of bat tissues all showed fungal structures similar to those of G. destructans. (ii) G. destructans DNA was directly amplified from infected bat tissues, (iii) Isolations of G. destructans in cultures from infected bat tissues showed 100% DNA match with the fungus present in positive tissue samples. (iv) RAPD patterns for all G. destructans cultures isolated from two sites were indistinguishable. (v) The fungal isolates showed psychrophilic growth. (vi) We identified in vitro proteolytic activities suggestive of known fungal pathogenic traits in G. destructans.
Further studies are needed to understand whether G. destructans WNS is a symptom or a trigger for bat mass mortality. The availability of well-characterized G. destructans strains should promote an understanding of bat–fungus relationships, and should aid in the screening of biological and chemical control agents.

Related:

• Colony Collapse Disorder

As the premier managed pollinator, the western honey bee, Apis mellifera, contributes more than $14 billion to USA agriculture annually. Beginning in 2006, the American apiculture industry experienced catastrophic losses of unknown origin. The phenomenon, called colony collapse disorder (CCD), was identified by a set of distinctive characteristics, including the absence of dead bees in or near the colony and the presence of abundant brood, honey, and pollen despite vastly reduced numbers of adult workers.

To differentiate among possible explanations for CCD, a new study used whole-genome microarray analysis, comparing gut gene expression in adult worker bees from healthy and CCD colonies. Researchers assayed the gut because it is the principal site of pesticide detoxification and an integral component in the immune defense against pathogens in A. mellifera. Samples from colonies varying in CCD severity were collected on the U.S. east and west coasts in the winter of 2006–2007 and compared with healthy “historical” controls collected in 2004 and 2005.

No simple explanations for the cause of CCD emerge from the microarray analysis. Although gene transcript analysis did not clearly identify a specific cause for CCD, this study documents several patterns possibly suggestive of a causal mechanism. The reduced protein synthetic capabilities that would accompany ribosomal hijacking by multiple picorna-like viruses would leave bees unable to respond to additional stresses from pesticides, nutrition, or pathogens. Although any interpretation of the presence of these rRNA fragments is speculative, the reported interaction between bee picorna-like viruses and rRNA is suggestive of a possible root cause of CCD.

Changes in transcript abundance relating to colony collapse disorder in honey bees (Apis mellifera). PNAS USA August 24 2009 doi: 10.1073/pnas.0906970106
Colony collapse disorder (CCD) is a mysterious disappearance of honey bees that has beset beekeepers in the United States since late 2006. Pathogens and other environmental stresses, including pesticides, have been linked to CCD, but a causal relationship has not yet been demonstrated. Because the gut acts as a primary interface between the honey bee and its environment as a site of entry for pathogens and toxins, we used whole-genome microarrays to compare gene expression between guts of bees from CCD colonies originating on both the east and west coasts of the United States and guts of bees from healthy colonies sampled before the emergence of CCD. Considerable variation in gene expression was associated with the geographical origin of bees, but a consensus list of 65 transcripts was identified as potential markers for CCD status. Overall, elevated expression of pesticide response genes was not observed. Genes involved in immune response showed no clear trend in expression pattern despite the increased prevalence of viruses and other pathogens in CCD colonies. Microarray analysis revealed unusual ribosomal RNA fragments that were conspicuously more abundant in the guts of CCD bees. The presence of these fragments may be a possible consequence of picorna-like viral infection, including deformed wing virus and Israeli acute paralysis virus, and may be related to arrested translation. Ribosomal fragment abundance and presence of multiple viruses may prove to be useful diagnostic markers for colonies afflicted with CCD.

Related:

• Colony Collapse Disorder
• The great bee swindle – colony collapse disorder
• Bee-Killing Parasite Genome Sequenced
• Microbial diseases of bees

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.

Related:

• Colony Collapse Disorder
• The great bee swindle – colony collapse disorder
• To bee or not to bee