Summary auto-generated
This study demonstrates that inteins—protein sequences excised during maturation of the DNA gyrase A subunit (GyrA)—represent consistent taxonomic markers in mycobacteria. The researchers analyzed multiple isolates of five mycobacterial species using PCR amplification and DNA sequencing. Mycobacterium malmoense, M. marinum, M. ulcerans, and M. xenopi each showed uniform patterns: M. malmoense and most other species consistently contained or lacked GyrA inteins. However, M. kansasii displayed heterogeneity, with two genetically distinct subspecies differing in intein presence. Type I M. kansasii (all 13 isolates) possessed inteins, while type II (all 10 isolates) lacked them. This correlation with genetic subspecies classification suggests inteins mark significant taxonomic divisions. The GyrA inteins showed conserved structural features including insertion position, size (approximately 420 amino acids in most species), and splice junctions, indicating a specific evolutionary origin. The authors conclude that GyrA intein presence/absence is not random but defines mycobacterial taxa at species or subspecies levels, with potential applications in bacterial classification and identification.
Key findings
- GyrA inteins function as consistent taxonomic markers in mycobacteria, with presence or absence characteristic of specific species or subspecies
- M. kansasii comprises two genetically distinct subspecies that perfectly correlate with GyrA intein status: type I contains inteins while type II lacks them
- Other mycobacterial species (M. malmoense, M. marinum, M. ulcerans) show uniform intein patterns across all tested isolates, consistent with genetic homogeneity
- GyrA inteins share conserved features including insertion position following codon 130, similar amino acid composition, and C-terminal splice junctions across species
- M. xenopi possesses a unique shorter GyrA intein (198 amino acids) that lacks homing endonuclease activity and shows evidence of complex recombination
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Abstract
The A subunit of DNA gyrase in mycobacteria is frequently subjected to splicing events as its gene, gyrA, harbours an insertion encoding an intein. Investigation of a number of different isolates of Mycobacterium kansasii, Mycobacterium malmoense, Mycobacterium marinum, Mycobacterium ulcerans and Mycobacterium xenopi demonstrated that the presence of GyrA inteins is not random but a taxonomic character specific for a given taxon at a species or subspecies level.