The Obligate Predatory Bdellovibrio bacteriovorus Possesses a Neutral Lipid A Containing α-D-Mannoses That Replace Phosphate Residues

Abstract

Bdellovibrio bacteriovorus are predatory bacteria that penetrate Gram-negative bacteria and grow intraperiplasmically at the expense of the prey. It was suggested that B. bacteriovorus partially degrade and reutilize lipopolysaccharide (LPS) of the host, thus synthesizing an outer membrane containing structural elements of the prey. According to this hypothesis a host-independent mutant should possess a chemically different LPS. Therefore, the lipopolysaccharides of B. bacteriovorus HD100 and its host-independent derivative B. bacteriovorus HI100 were isolated and characterized by SDS-polyacrylamide gel electrophoresis, immunoblotting, and mass spectrometry. LPS of both strains were identified as smooth-form LPS with different repeating units. The lipid As were isolated after mild acid hydrolysis and their structures were determined by chemical analysis, by mass spectrometric methods, and by NMR spectroscopy. Both lipid As were characterized by an unusual chemical structure, consisting of a ␤-(136)-linked 2,3-diamino-2,3-dideoxy-D-glucopyranose disaccharide carrying six fatty acids that were all hydroxylated. Instead of phosphate groups substituting position O-1 of the reducing and O-4 of the nonreducing end ␣-D-mannopyranose residues were found in these lipid As. Thus, they represent the first lipid As completely missing negatively charged groups. A reduced endotoxic activity as determined by cytokine induction from human macrophages was shown for this novel structure. Only minor differences with respect to fatty acids were detected between the lipid As of the hostdependent wild type strain HD100 and for its hostindependent derivative HI100. From the results of the detailed analysis it can be concluded that the wild type strain HD100 synthesizes an innate LPS.

The Structure of a Novel Neutral Lipid A from the Lipopolysaccharide of Bradyrhizobium elkanii Containing Three Mannose Units in the Backbone

“…The third mannose unit was a-(1!1)-linked to the reducing GlcpN3N residue. Such a lipid A structure has not yet been identified in rhizobial LPS, however, it resembles the lipid A isolated from Bdellovibrio bacteriovorus, [26] which contained two mannose residues that decorated the backbone at C-4' and C-1. Another example of mannose-containing lipid A is that derived from the phototrophic bacterium Rhodomicrobium vanniellii, in which the C-4' of the phosphate-free GlcpN disaccharide backbone was substituted by a mannose residue.…”

Occurrence of an Unusual Hopanoid-containing Lipid A Among Lipopolysaccharides from Bradyrhizobium Species

“…Mannose-containing lipid A samples were identified earlier in the predatory bacterium Bdellovibrio bacteriovorus, where mannose residues occupied positions C-1 and C-4Ј of the D-GlcpN3N-disaccharide (49), and in phototrophic bacterium Rhodomicrobium vannielli (50), in which the C-4Ј of the glucosaminyl disaccharide backbone was occupied by one mannose residue. Recently, we reported the presence of a neutral mannose-containing lipid A in LPS of B. elkanii USDA 76 (21).…”

Bacterial Lipopolysaccharides: An Overview of Their Structure, Biosynthesis and Immunological Activity

“…Moreover, phosphate groups can be substituted by further phosphate groups, producing a pyrophosphate, but also by other polar substituents, such as 4-amino-4-deoxy-L-arabinopyranose (arabinosamine, Arap4N) and 2-amino-ethanol groups (EtN), or by acid residues, such as galacturonic acid (GalpA). Phosphate groups can be absent as in the case of Bdellovibrio bacteriovorus LPS lipid A that is characterized by the replacement of phosphate groups with two mannose residues, generating a totally neutral lipid A [27]. Exceptionally, the lipid A of the marine bacterium Loktanella rosea has a very unusual structure, as the molecule is non-phosphorylated, both GlcpN residues are β-linked, and the GlcpN I forms with α-GalpA a unique mixed trehalose-like structure [28].…”