## 3 A Brief Overview of AHL Systems in _Burkholderia_
### Burkholderia pseudomallei _Group_
#### 3.2.2. Burkholderia pseudomallei  
The _B. pseudomallei_ genome has been identified as having three _luxI/R_ pair homologs, namely _bpsI1/R1_, _bpsI2/R2_, and _bpsI3/R3_, and two orphan or solo _luxR_ regulator homologs, designated as _bpsR4_ and _bpsR5_. With the exception of _bpsR5_, which is present on chromosome 1, most of the QS genes are present on chromosome 2 [61].  
The major AHL produced by BpsI1 is C8-HSL(_N_-octanoyll-L-homoserine lactone), whereas BpsI2 and BpsI3 are associated predominantly with _N_-3-hydroxy-octanoyll homoserine lactone (OHC8-HSL) and _N_-3-hydroxy-decanoyll homoserine lactone (OHC10-HSL) respectively [62]. _bpsI1_ is divergently transcribed to _bpsR1_, representing the M1 topology, and is separated by an intergenic region which contains an ORF homologous to _rsaM_. _bpsI2_ is transcribed in the same direction as _bpsR2_, representing the M3 topology, and is separated by two to seven genes, one of which is a _rsaM_ homolog. _bpsI3_ is also transcribed in the same direction as _bpsR3_ but is not separated by any of the intergenic ORFs and represents the R1 topology.  
The local topological patterns and location of QS genes in members of the _B. pseudomallei_ group are shown in Table 5.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Species** & **QS system** & **ID** & **Gene topology** & **Chr.** & **Major AHL** & **Comments** \\ \hline \multirow{6}{*}{_B. mallei_} & _bmaR3/bmaI3_ & R1 & & Chr2 & OCH8 & _B. mallei_ ATCC 23344 \\ \cline{2-7}  & _bmaR1/-/bmaI1_ & M1 & & Chr2 & C8 & Present in all _B. mallei_ strains \\ \cline{2-7}  & _bmaR3/-/bmaI3_ & X3 & Chr2 & OCH8 & _B. [PERSON]_ NCTC 10229 and _[PERSON]. [PERSON]_ \\ \cline{2-7}  & _bpsR3/bpsI3_ & R1 & Chr2 & OHC10 & Present in all _B. pseudomallei_ strains \\ \cline{2-7}  & _bpsR1/-/bpsI1_ & M1 & Chr2 & C8 & Present in all _B. pseudomallei_ strains \\ \cline{2-7}  & _bpsR2/-/bpsI2_ & M3 & Chr2 & OHC8 & Present in all _B. pseudomallei_ strains \\ \cline{2-7}  & _bpsR2/-/bpsI2_ & M3 & Chr2 & OHC8 & Present in all _B. pseudomallei_ strains \\ \cline{2-7}  & _bpsdomallei_ & & & & Present in some strains such as \\ \cline{2-7}  & _-/-_ & X3 & Chr2 & Chr2 & _B. pseudomallei_ 1026b, \\ \cline{2-7}  & _-/-_ & & & & _B. pseudomallei_ MSHR346, \\ \cline{2-7}  & _bpsl/bpsR_ & R2 & & & _B. pseudomallei_ 112 _etc._ \\ \hline \hline \end{tabular}
\end{table}
Table 5: QS topologies in the _Burkholderia pseudomallei_ group.  
The location of the QS genes within the circular chromosome 2 also shows similarities between genomes even though the conservation is stronger in _B. pseudomallei_ than in _B. mallei_ (Figure 5).  
QS regulation of _B. pseudomallei_ is rather complex and hierarchical. BpsR1 regulates _bpsI1_ in the presence of a cognate AHL in a positive feedback loop. BpsR5 also partially activates _bpsR1. bpsI2_ is constitutively expressed and its expression is enhanced by each of the BpsR--especially by BpsR1 and BpsR3--in the presence of 3-oxo-C8 HSL. _bpsI3_ is also constitutively expressed but its expression is repressed in the presence of any BpsR protein, although the repression is less in the case of BpsR3 [61] (Figure 6).