biosynthetic intermediate lyso-ornithine lipid.
Ornithine lipids and their structural modifications: ..
To study if OL biosynthesis and/or modification are under control of PhoB the genome sequence of A. tumefaciens C58 was searched for the presence of putative Pho boxes. A PSSM was constructed using Pho box sequences reported previously for S. meliloti 1021 (). Escherichia coli sequences were excluded for matrix construction. Sequences used for matrix construction are listed in . The program Info-Gibbs () was used for matrix construction. One motif per sequence was expected and the desired matrix size was fixed to 18 bp. As background model the regions upstream of A. tumefaciens C58 genes were employed. The resulting matrix has a maximum score for putative Pho boxes of 12.4, and the threshold used for the search was set to 7. The program Matrix-scan () was used to search the A. tumefaciens C58 genome for the presence of Pho boxes. The Markov order used was 0. Again the upstream regions of genes from A. tumefaciens C58 were employed as the background model. The search was performed scanning the upstream regions of predicted genes in 18 bp windows and comparing them with the PSSM. This search was performed for both strands. The list of genes presenting putative upstream Pho boxes was analysed for the presence of OL biosynthesis genes olsB, olsE and genes coding for glycosyltransferases ().
(2012), Ornithine lipids and their structural modifications: from ..
Agrobacterium tumefaciens wild-type A208 and mutants deficient in OL biosynthesis were grown in Sherwood minimal medium with high (1.3 mM) or low phosphate (20 μM) concentrations. Under high phosphate conditions the phospholipids PC, PG, PE, dimethyl PE and CL were detected in the wild-type (). In addition, as observed earlier in cells grown on complex medium the two OLs S1 and S2 were detected. Under low phosphate conditions all phospholipids were reduced and both OLs increased to a total of about 45–50% in the wild-type. In addition, several new lipids were observed in the phosphate-deplete grown cells. In addition to DGTS several unknown lipids were detected. As and had observed the formation of glycolipids in R. sphaeroides and M. loti under low phosphate conditions we considered it a possibility that the unknown lipids were glycolipids. Naphthol staining of membrane lipids separated by TLC confirmed the presence of at least four different glycolipids. In contrast to S. meliloti and R. sphaeroides no sulfolipid was detected under phosphate starvation conditions which is consistent with the absence of genes coding for homologues involved in their biosynthesis in the A. tumefaciens genome. In the olsB-deficient mutant unable to form OLs increased amounts of DGTS can be detected in addition to increased amounts of the unknown lipids ().