Figure 1.
Genomic layout of the Burkholderia ITS.
Panel A shows diagram of bacterial rRNA operon in Burkholderia species, demonstrating the specific location of the 16S-23S ITS. Panel B shows low resolution genomic alignment generated from consensus sequences of known ITS sequences, to highlight 1) sequence similarity among ITS types and 2) regions of difference between ITS types. Sequence labels include ITS code followed by species designation as follows: Bp (B. pseudomallei), Bm (B. mallei), Bt (B. thailandensis), Bt-like (B. thailandensis-like, referring to the reference strain MSMB43) and Bok (B. oklahomensis). ITS sizes are described at the right. Black bars at the bottom highlight major regions of variability I, II, III and IV that contribute to ITS fragment length polymorphisms, which are further demonstrated in the sequence conservation plot. Note that peaks outside of regions I, II, III and IV correspond to rare frame-shift and single nucleotide mutations, and are primarily the result of alignment with B. oklahomensis, whose ITS sequence is most divergent. Dotted lines represent missing sequences.
Table 1.
The genomic locations of rrn operons are conserved in B. pseudomallei.
Table 2.
Burkholderia ITS coding scheme and average pair-wise similarities.
Figure 2.
Geographic distribution of B. pseudomallei ITS types.
ITS types are color coded. Pie chart sizes reflect the number of isolates characterized. Samples taken from sporadic melioidosis regions, as in Africa, Central and South America, frequently possessed ITS type G, shown in purple. Endemic melioidosis areas show a high degree of ITS diversity, but possessed very few isolates with the G allele (0.88% of Australian isolates and 0.68% of Thai isolates).
Figure 3.
Frequency distribution plot of B. pseudomallei ITS types in the primary regions of endemicity, Australia and Thailand.
ITS types C, E and CE were observed most frequently in these regions, while other ITS types were rarely observed. ITS type CE was observed 24% more often in Thailand as compared to Australia.
Figure 4.
ITS variable sequence block analysis overlaid onto a Burkholderia MLST phylogeny (modified from Gee et al. [37]).
The presence (+), absence (-) or partial absence (indicated by the Δ symbol) of variable ITS sequence blocks are described for major species-level Burkholderia clades, based on MLST sequence analysis. Because B. mallei is a clone of B. pseudomallei and possesses an identical ITS type, its clade was collapsed into that of B. pseudomallei.