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Publication ahead of print
Journal
Apidologie
DOI http://dx.doi.org/10.1051/apido/2010045
Published online 06 August 2010

© INRA/DIB-AGIB/EDP Sciences, 2010

1. INTRODUCTION

The microsporidia species Nosema apis and N. ceranae cause a destructive disease of honey bees, Apis mellifera L., worldwide (Bailey, 1991; Higes et al., 2006; Huang et al., 2007). Nosema affects adults only, infecting epithelial cells lining the midgut. Nosema often escapes notice due to its frequent lack of outward symptoms. The organism can cause digestive disorders, shorten bee life spans, reduce pollen collection, induce queen supercedure, decrease colony population, reduce honey production, and cause greater colony mortality in the winter. Efforts to control Nosema include removing older combs and treating hives with fumagillan. Observations indicate that Nosema is distributed by mailing and transportation of honey bees (Jay, 1966) and infective beekeeping materials (Klee et al., 2007) combined with migratory beekeeping practices (Giersch et al., 2009). Environmental reservoirs and non-honey bee vectors of Nosema spores may contribute to its epidemiology. For example, the range of the migratory bee-eating bird Merops apiaster includes Western Asia, and its regurgitated pellets have been shown to contain infective Nosema spores (Higes et al., 2008a). In 1913, Fantham and Porter demonstrated that N. apis is capable of infecting other insect species, though some of their results have been called into question through subsequent experiments (Bailey, 1991).

Recently an illness of A. mellifera, called “Colony Collapse Disorder” (CCD) or “Colony Loss” has been causing large-scale losses of honey bees in the United States (Chen et al., 2007) and in Europe (Topolska et al., 2008; Higes et al., 2008b). A possible contributor to CCD may be N. ceranae, a species of Nosema from Apis cerana that has been recently found in A. mellifera (Higes et al., 2006; Topolska et al., 2008; Vejsnaes et al., 2010; Paxton, 2010). Recent studies by Chauzat et al. (2007), Williams et al. (2008), Klee et al. (2007), Martín-Hernández et al. (2007), Paxton et al. (2007), Higes et al. (2009), Tapaszti et al. (2009), and Giersch et al. (2009) have revealed that N. ceranae is widespread in Africa, Europe, Australia, and North America. To date, N. ceranae has not been observed in Turkey. A previous study by Aydin et al. (2005) identified the presence of N.apis in honey bees from Turkey. However, this study did not attempt to distinguish N. apis from N. ceranae using molecular diagnostic methods.

The objectives of this study were to detect N. ceranae and N. apis from Turkish honey bees using PCR and to determine the genetic relationship of N. ceranae from Turkey relative to N. ceranae from other countries.

2. MATERIALS AND METHODS

2.1. Sample collection

Samples were collected by one of the authors (M.K.) from beekeepers in 2005 and 2006 from 20 provinces in Turkey (Tab. I). Five to 20 worker honey bees were placed in a plastic liquid scintillation vial containing 70% ethanol.

thumbnail Figure 1

PCR products of N. ceranae and N. apis: Lane 1: N. ceranae positive sample; Lane 2: N. apis (269 bp) and N. ceranae (250 bp) control; Lane 3: 50 bp DNA ladder.

2.2. DNA extraction

The Puregene DNA extraction kit (Gentra, Minneapolis, MN) was used to obtain DNA from honey bee abdomens using a procedure similar to Magnus and Szalanski (2010). Abdomens from two bees from each sample were allowed to air dry before adding the samples to cell lysis buffer. Extracted DNA was resuspended in 50 ul of Tris: EDTA buffer (pH 8.0), and stored at –20 °C until PCR.

2.3. PCR amplification

Polymerase chain reaction specific for the rRNA marker for N. ceranae and N. apis was conducted using the primers N. ceranae F and N. ceranae R and N. apis sense and antisense per Chen et al. (2008, 2009). These primers were used together for a multiplex PCR reaction and resulted in a 250 bp amplicon of the small subunit (16S) ribosomal RNA gene for N. ceranae and a 269 bp amplicon for N. apis (Fig. 1). Positive controls consisted of N. ceranae from honey bees collected from Nebraska, USA, and N. apis from honey bees collected from Beaverlodge, Alberta, Canada. In addition, a negative control was included for most PCR runs. For PCR 2 μL of DNA template was used for the 50 μL multiplex PCR. Concentration of reagents, other than PCR primers, is provided in Szalanski and McKern (2007). The PCR thermocycler profile consisted of 40 cycles of a 94 °C for 45 s, 58 °C for 45 s, and 72 °C for 60 s, with a final extension of 5 min at 72 °C. Amplicons were run on a 2% agarose gel electrophoresis, and products were visualized under UV.

Table I

Prevalence of N. ceranae and N. apis in different regions of Turkey.

2.4. DNA sequencing

Three positive N. ceranae PCR samples were subjected to DNA sequencing. For these samples a 208 bp region of the 16S gene was subjected to PCR using the primers Nosema F/Nosema R (Chen et al., 2008) using the thermocycler profile outlined above. Once PCR products were purified using Microcon-PCR Filter Units (Millipore, Bedford, MA), they were sent to the University of Arkansas Medical Sciences DNA Sequencing Core Facility (Little Rock, AR) for direct sequencing in both directions. CLUSTAL W (Thompson et al., 1994) and Bioedit v5.0.7 software (Hall, 1999) were used to align DNA sequences.

A BLAST search (http://blast.ncbi.nlm.nih.gov) was used to compare genetic variation of the 208 bp amplicons from Turkey with those available on GenBank. Genealogy of N. ceranae 16S genotypes from our lab and from GenBank was determined using the method of Templeton et al. (1992), which represent the evolutionary steps between genotypes, using TCS v 1.21 (Clement et al., 2000).

3. RESULTS

From the 84 samples subjected to PCR analysis, N. ceranae was amplified one time in each from samples from the provinces of Artvin, Hatay, and Muğla (Tab. I, Fig. 2). Nosema apis was detected one time each from the provinces of Sivas, Izmir, Bitlis and Gaziantep (Tab. I, Fig. 2). These positive samples were from beekeepers located at widely dispersed geographical regions in Turkey, including the Aegean, Mediterranean, South East Anatolia, Central Anatolia, and the Black Sea. The only region we found to have A. mellifera positive for both N. apis and N. ceranae infection was the Aegean region.

thumbnail Figure 2

Map of Turkey showing provinces from which A. mellifera were collected and tested for N. ceranae and N. apis. The number of samples screened is provided along with the numbers positive for N. ceranae and N. apis, respectively, in parentheses.

Table II

Mitochondrial DNA haplotypes of Nosema ceranae using a 208 bp region of the rDNA 16S gene.

From the three positive N. ceranae samples from Turkey, no intraspecific DNA sequence variation was observed among the 208 bp 16S sequences. Using the N. ceranae 16S DNA sequences available on GenBank, a total of 6 different genotypes, designated as genotypes G1-G6, were found using the same 208 bp region used in this study (Tab. II, Fig. 3). A BLAST search revealed that the N. ceranae DNA 208 bp sequence from Turkey, designated as genotype 2 (G2), was identical to N. ceranae DNA sequences from the United States, Europe, and Australia. TCS spanning network of the N. ceranae genotypes revealed that genotype G2 was the basal type, which was one base pair different with other genotypes, except for G3 and G6 (Fig. 3). Genotype G2 can be considered as the basal ancestral genotype because it is located at the base of the genealogy. Genotype G3 was the most distantly related to G2, with three base pair differences, and only occurred in Australia (GenBank accession number FJ789791).

thumbnail Figure 3

Genealogical relationships among 16S genotypes of Nosema ceranae estimated by TCS (Clement et al. 2000). A unit branch represents one mutation and small ovals indicate genotypes that were not observed.

4. DISCUSSION

This study demonstrated that both N. apis and N. ceranae are present in honey bees from the Republic of Turkey. N. ceranae was observed in geographically distant regions of Turkey, including the Aegean, Mediterranean and Black Sea. Aydin et al. (2005) found Nosema sp. from six regions in Turkey, with the majority occurring in Marmara and the Black Sea. We did not find N. apis or N. ceranae in Marmara, Central Anatolia, or East Anatolia, but we did find it in Southeast Anatolia, a region where Nosema sp. was not detected by Aydin et al. (2005).

Our finding of three positive N. ceranae samples out of 84 (3.6%) is on the low end of the spectrum, relative to the frequency of N. ceranae (65.6%) in samples from France in 2002–2005 (Chauzat et al., 2007), Minnesota in the United States (40%), three Canadian provinces (19.6%) (Williams et al., 2008), and in Australia in 2008 (4.5–33.7%) (Giersch et al., 2009). This number is provided for comparison only and should be interpreted with caution. The goal of our study was only to detect the presence or absence of N. ceranae and N. apis in Turkey. Our sample size of 2 bees per colony is insufficient to provide a statistically significant measurement of Nosema prevalence.

Some of the Turkish provinces are overrepresented as compared to others, but the samples are representative of a wide number of subclimates and are from locations spanning the entire country. Samples used for our N.apis, N. ceranae PCR study were previously used for a population genetics study of A. mellifera in Turkey (Solorzano et al., 2009). The N. ceranae positive honey bee samples belonged to mtDNA COI-COII ‘C’ lineage mitotypes, C11 (Artvin), and C12 (Hatay and Muğla), and the N. apis positive samples belonged to the mitotypes C12 (Izmir and Bitlis), C13 (Sivas) and C19 (Gaziantep). To our knowledge, no other studies on molecular detection of N. ceranae or N. apis have documented the genetic lineage or mitotype of the host bees, so the relationship of N. ceranae infection and different host lineages is unknown. All of the three provinces (Artvin, Hatay, and Muğla) where N. cerenae were detected also showed high rates of colony losses in 2006/2007 (Giray et al., 2010). For Artvin province, 50% of 2505 colonies maintained by 44 beekeepers were lost, while 39.4% of 7628 colonies maintained by 36 beekeepers in Hatay province were lost, and 22.7% of 6516 colonies maintained by 36 beekeepers were lost in Muğla province. Though the cause of the colony losses cannot be conclusively attributed to N. ceranae infection, there exists a potentially significant relationship between its presence and the occurrence of the losses. Similar colony loss reports that may be attributed to N. ceranae have been documented in Poland (Topolska et al., 2008) and Denmark (Vejsnaes et al., 2010).

The high level of genetic similarity of 16S rDNA sequences of N. ceranae from Turkey relative to those found elsewhere complicates efforts to determine a geographic origin for N. ceranae, as well as efforts to identify strains with varying degrees of virulence. DNA sequencing analysis of a larger region of 16S rDNA, or the use of additional genetic markers may provide additional insight. It is perhaps not surprising that N. ceranae should be found in Turkey, as it is close to the native range of the original host of N. ceranae, the Asiatic honey bee A. cerana F., which is found from Western Afghanistan to Japan (Dietz, 1992). The minor variation found between strains of N. ceranae encourages shifts in future emphases on research from finding differences in parasitic virulence perhaps to evaluating different N. ceranae genes for variation and to finding differences in honey bee lineage susceptibility, and examining climatic and environmental variables involved in N. ceranae prevalence and transmission. It may be that certain bee lineages are more or less able to cope with N. ceranae infection, or simply that an increase in their genetic diversity through breeding programs or interbreeding with feral “survivor” populations will provide them with more mechanisms to adapt. In addition, the potential role of climatic and environmental variables should not be ignored.

Acknowledgments

The authors would like to express their gratitude to the Ministry of Agriculture and Rural Affairs of Turkey, beekeepers and colleagues for their assistance in the collection of honey bee specimens in Turkey and Ray Fisher at the University of Arkansas for Adobe Illustrator assistance. This research was supported in part by the University of Arkansas, Arkansas Agricultural Experiment Station, TUBITAK and the Middle East Technical University, Ankara, Turkey.

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All Tables

Table I

Prevalence of N. ceranae and N. apis in different regions of Turkey.

Table II

Mitochondrial DNA haplotypes of Nosema ceranae using a 208 bp region of the rDNA 16S gene.

All Figures

thumbnail Figure 1

PCR products of N. ceranae and N. apis: Lane 1: N. ceranae positive sample; Lane 2: N. apis (269 bp) and N. ceranae (250 bp) control; Lane 3: 50 bp DNA ladder.

In the text
thumbnail Figure 2

Map of Turkey showing provinces from which A. mellifera were collected and tested for N. ceranae and N. apis. The number of samples screened is provided along with the numbers positive for N. ceranae and N. apis, respectively, in parentheses.

In the text
thumbnail Figure 3

Genealogical relationships among 16S genotypes of Nosema ceranae estimated by TCS (Clement et al. 2000). A unit branch represents one mutation and small ovals indicate genotypes that were not observed.

In the text