Heterogeneity in Bacillus cereus PCR Products Detected by ESI−FTICR Mass Spectrometry

Abstract
PCR amplification of a segment of the 16/23S rDNA interspace region (ISR) from Bacillus cereus 6464 produced a mixture of products. An 89-bp product was predicted on the basis of the reported sequence. The ESI−FTICR analysis revealed three double-stranded products, differing in size by a single nucleotide corresponding to two homoduplexes of 89 and 88 base pairs and a heteroduplex of 89 and 88 nucleotide strands. These were produced from a single preparation of genomic DNA and a single primer pair. ESI−FTICR analysis of the single strands identified a deletion of a T in the coding strand and a corresponding loss of an A in the noncoding strand of this product. The ESI−FTICR analysis indicated the presence of an unreported sequence variation between rRNA operons in this organism. This report illustrates that PCR products amplified from templates differing by a single nucleotide can be resolved and identified using ESI−FTICR at the 89-bp level. Furthermore, the ESI−FTICR mass measurements provided the identity of the deletion, which is indicative of interoperon variability.

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