Gibbons et al. (2000) had isolated a gene

from Salmonella responsible for the introduction of a 2-hydroxyl group into a lipid-A-bound myristic acid residue. The hydroxylation reaction is catalyzed by the Fe2+/O2/α-ketoglutarate-dependent LpxO dioxygenase. Rojas-Jiménez et al. (2005) had identified a gene called olsC in R. tropici encoding an LpxO homolog responsible for the synthesis of hydroxylated OLs. Later, it was shown that OlsC is responsible for the introduction of a hydroxyl group in the C-2 position of the piggy-back fatty acid of OLs (Vences-Guzmán et al., 2011). A prediction indicates that OlsC of R. tropici CIAT899 is a water-soluble protein of 281 LY2109761 price amino acids (Rojas-Jiménez et al., 2005). Owing to its homology to LpxO from Salmonella, it can be expected that OlsC-dependent hydroxylation of the ester-linked fatty acid will also be Fe2+/O2/α-ketoglutarate dependent. Genes encoding OlsC homologs can be found in compound screening assay Agrobacterium vitis, Agrobacterium radiobacter, Ochrobactrum anthropi, Ochrobactrum intermedium, Aurantimonas manganoxydans, Fulvimarina pelagi, Roseomonas cervicalis, Chelativorans sp., Mycobacterium rhodesiae, and several Brucella species (Supporting

Information, Table S1). Interestingly, in the so-called classical Brucella such as Brucella ovis, Brucella suis, Brucella melitensis, or B. abortus, which are intracellular pathogens, the olsC gene is present only as pseudogene containing a frameshift mutation. As a consequence, the olsC gene is translated into two ORFs, making the gene olsC nonfunctional (Palacios-Chaves et al., 2011). In the genomes of several atypical Brucella strains such as Brucella microti, Brucella sp. BO1, or Brucella sp. BO2 which share several characteristics with the opportunistic soil pathogen Ochrobactrum, olsC genes lacking the frameshift can

be detected that are probably functional. This observation implies that organisms like Ochrobactrum, R. tropici, and nonclassical Brucella such as Brucella isolated from soil that present unless both (De et al., 2008;Scholz et al., 2008a, 2008b, 2009, 2010) an intracellular and a free-living lifestyle have preserved a functional copy of olsC, whereas the classical Brucella strains that are strictly intracellular pathogens present only a nonfunctional copy of olsC (Palacios-Chaves et al., 2011). A functional OlsC might confer a selective advantage in adverse abiotic stress conditions, but might not be of use or even have a negative impact when the bacteria are inside a host. Recently, Vences-Guzmán et al. (2011) reported a more detailed study of an olsC-deficient R. tropici mutant. Strains lacking the OL hydroxylase OlsC showed a growth defect at increased temperatures (37 and 42 °C) and under acid pH conditions (4.5 and 4.0).