Hydroxylated ornithine lipids increase stress tolerance in Rhizobium tropici CIAT899

Abstract

SummaryOrnithine lipids (OLs) are widespread among Gramnegative bacteria. Their basic structure consists of a 3-hydroxy fatty acyl group attached in amide linkage to the a-amino group of ornithine and a second fatty acyl group ester-linked to the 3-hydroxy position of the first fatty acid. OLs can be hydroxylated within the secondary fatty acyl moiety and this modification has been related to increased stress tolerance. Rhizobium tropici, a nodule-forming a-proteobacterium known for its stress tolerance, forms four different OLs. Studies of the function of these OLs have been hampered due to lack of knowledge about their biosynthesis. Here we describe that OL biosynthesis increases under acid stress and that OLs are enriched in the outer membrane. Using a functional expression screen, the OL hydroxylase OlsE was identified, which in combination with the OL hydroxylase OlsC is responsible for the synthesis of modified OLs in R. tropici. Unlike described OL hydroxylations, the OlsE-catalysed hydroxylation occurs within the ornithine moiety. Mutants deficient in OlsE or OlsC and double mutants deficient in OlsC/OlsE were characterized. R. tropici mutants deficient in OlsCmediated OL hydroxylation are more susceptible to acid and temperature stress. All three mutants lacking OL hydroxylases are affected during symbiosis.

OlsG (Sinac_1600) Is an Ornithine Lipid N-Methyltransferase from the Planctomycete Singulisphaera acidiphila

“…Three OL hydroxylases introducing hydroxyl groups at the 2-position of the ester-bound fatty acid (OlsC), at the 2-position of the amide-bound fatty acid (OlsD), or within the ornithine head group (OlsE) have been described in recent years (6 -9). Evidence points at a role for some of these OL hydroxylations in the bacterial response to abiotic stress conditions, such as high temperature or acidity (9). Furthermore, Agrobacterium tumefaciens and Rhizobium tropici mutants deficient in OL formation or OL hydroxylation were affected in host-symbiont/host-pathogen interactions (9,10).…”

“…Evidence points at a role for some of these OL hydroxylations in the bacterial response to abiotic stress conditions, such as high temperature or acidity (9). Furthermore, Agrobacterium tumefaciens and Rhizobium tropici mutants deficient in OL formation or OL hydroxylation were affected in host-symbiont/host-pathogen interactions (9,10).…”

Accumulation of Novel Glycolipids and Ornithine Lipids in Mesorhizobium loti under Phosphate Deprivation

“…Three genes are known to be responsible for hydroxylation of OL. OlsC and OlsE are found in Rhizobium and Agrobacterium hydroxylating the C-2 position of the ester-linked fatty acid and the ornithine head group, respectively (4,16). A recently discovered hydroxylase, OlsD, forms OL-OH with the OH-group linked to the amide-bound fatty acid (15).…”

“…Deuterated solvents were purchased from Deutero GmbH (Kastellaun, Germany). Prior to NMR analysis, MGlcD was per-O-acetylated with acetic anhydride in pyridine (1:2) and further purified as described previously (16 13 C assignment were obtained normally from two-dimensional 1 H, 13 C-heteronuclear multiple bond correlation (HMBC) and 1 H, 13 C-HSQC-TOCSY. Absolute configuration of ornithine in ornithine lipids.…”

“…There are several modifications of OL with respect to hydroxylation of different positions in the molecule. The inserted hydroxy group can be found at one of the two fatty acids and/or the ornithine head group (4,15,16). The position of the hydroxy group of the ester-linked fatty acid was resolved with gas chromatographymass spectrometry (GC-MS) at C-2 (16), while there are no structural details available on the positions of the hydroxy groups inserted at the amide-bound fatty acid or at the head group.…”