Abstract
The genus Burkholderia sensu lato is composed of a diverse and metabolically versatile group of bacterial species. One characteristic thought to be unique for the genus Burkholderia is the presence of two forms each (with and without 2-hydroxylation) of the membrane lipids phosphatidylethanolamine (PE) and ornithine lipids (OLs). Here, we show that only Burkholderia sensu stricto strains constitutively form OLs, whereas all other analyzed strains belonging to the Burkholderia sensu lato group constitutively form the two forms of PE, but no OLs. We selected two model bacteria to study the function of OL in Burkholderia sensu lato: (1) Burkholderia cenocepacia wild-type which constitutively forms OLs and its mutant deficient in the formation of OLs and (2) Robbsia andropogonis (formerly Burkholderia andropogonis) which does not form OL constitutively, and a derived strain constitutively forming OLs. Both were characterized under free-living conditions and during pathogenic interactions with their respective hosts. The absence of OLs in B. cenocepacia slightly affected bacterial growth under specific abiotic stress conditions such as high temperature and low pH. B. cenocepacia lacking OLs caused lower mortality in Galleria mellonella larvae while R. andropogonis constitutively forming OLs triggers an increased formation of reactive oxygen species immediately after infection of maize leaves, suggesting that OLs can have an important role during the activation of the innate immune response of eukaryotes.
Highlights
One major function of amphiphilic lipids is to form the lipid bilayer of membranes which serve as semipermeable barriers and limit a cell
We show that only Burkholderia s.s. species which often correspond to pathogens of humans, plants or animals constitutively form ornithine lipids (OLs) and that these lipids are absent in the recently proposed genera Paraburkholderia, Caballeronia, Robbsia, Trinickia, and Mycetohabitans that are related to beneficial bacteria or that do not cause pathogenicity in humans
The absence of OLs is probably not caused by the absence of a copy of the olsB gene because we found that all analyzed species possessed a gene encoding a homolog of the N-acyltransferase OlsB (Bcal1281) responsible for the first step in OL synthesis in B. cenocepacia (González-Silva et al, 2011)
Summary
One major function of amphiphilic lipids is to form the lipid bilayer of membranes which serve as semipermeable barriers and limit a cell. Ornithine Lipids in Burkholderia which have been found only in bacteria and are apparently absent in eukaryotes or archaea Their basic structure is composed of a 3-hydroxylated fatty acid linked by an amide bond to the α-amino group of ornithine and a second fatty acid linked by an ester bond to the 3-hydroxyl group of the first fatty acid (Geiger et al, 2010; Sohlenkamp and Geiger, 2016). The presence of OLs or an increased accumulation of OLs have been related to resistance to abiotic stress conditions or to a function during interactions with eukaryotic hosts like an increased persistence (Kim et al, 2018)
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