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SSU rRNA gene sequences for all unique Microsporidia detected in Bombus spp

Characterisation of microsporidian species and differentiation among genetic variants of the same species has typically relied on ribosomal RNA (rRNA) gene sequences.

We characterised the entire rRNA gene of a microsporidium from 11 isolates rep-resenting eight different European bumblebee (Bombus) species. We demonstrate that the microsporidium Nosema bombi infected allhosts that originated from a wide geographic area.

A total of 16 variable sites (all single nucleotid polymorphisms (SNPs)) were detected in the small subunit (SSU) rRNA gene and 42 (39 SNPs and 3 indels) in the large subunit (LSU) rRNA sequence. Direct sequencing of PCR-amplified DNA products of the internal transcribed spacer (ITS) region revealed identical sequences in all isolates.

In contrast, ITS fragment length determined by PAGE and sequencing of cloned amplicons gave better resolution of sequences and revealed multiple SNPs across isolates and two fragment sizes in each isolate (six short and seven long amplicon variants). Genetic variants were not unique to individual host species.

Moreover, two or more sequence variants were obtained from individual bumblebee hosts, suggesting the existence of multiple, variable copies of rRNA in the same microsporidium, and contrary to that expected for a class of multi-gene family under concerted evolution theory. Our data on within-genome rRNA variability call into question the usefulness of rRNA sequences to characterise intraspecific genetic variants in the Microsporidia and other groups of unicellular organisms.

The results have been published in Journal of Eukaryotic Microbiology 52(6), 505-513.

The results will be important for future studies of Microsporidia genetics as well as for population genetics of this important group of parasites.

Reported by

Queen's University of Belfast
School of Biol & Biochem., 97 Lisburn Road
72076 Belfast
United Kingdom
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