Structural and Biological Diversity of Lipopolysaccharides from Burkholderia pseudomallei and Burkholderia thailandensis

Abstract

Burkholderia pseudomallei, the etiological agent of melioidosis, is a facultative intracellular pathogen. As B. pseudomallei is a gram-negative bacterium, its outer membrane contains lipopolysaccharide (LPS) molecules, which have been shown to have low-level immunological activities in vitro. In this study, the biological activities of B. pseudomallei LPS were compared to those of Burkholderia thailandensis LPS, and it was found that both murine and human macrophages produced levels of tumor necrosis factor alpha, interleukin-6 (IL-6), and IL-10 in response to B. pseudomallei LPS that were lower than those in response to B. thailandensis LPS in vitro. In order to elucidate the molecular mechanisms underlying the low-level immunological activities of B. pseudomallei LPS, its lipid A moiety was characterized using mass spectrometry. The major lipid A species identified in B. pseudomallei consists of a biphosphorylated disaccharide backbone, which is modified with 4-amino-4-deoxy-arabinose (Ara4N) at both phosphates and penta-acylated with fatty acids (FA) C 14:0 (3-OH), C 16:0 (3-OH), and either C 14:0 or C 14:0 (2-OH). In contrast, the major lipid A species identified in B. thailandensis was a mixture of tetra-and penta-acylated structures with differing amounts of Ara4N and FA C 14:0 (3-OH). Lipid A species acylated with FA C 14:0 (2-OH) were unique to B. pseudomallei and not found in B. thailandensis. Our data thus indicate that B. pseudomallei synthesizes lipid A species with long-chain FA C 14:0 (2-OH) and Ara4N-modified phosphate groups, allowing it to evade innate immune recognition.

Alteration of the Phenotypic and Pathogenic Patterns of Burkholderia pseudomallei that Persist in a Soil Environment

“…The C 14:0 2-OH FA has been documented to be a feature that distinguishes virulent B. pseudomallei strains from non-virulent Burkholderia thailandensis strains. 48 After incubation in soil environments, no significant difference in the proportion of C 14:0 2-OH FA in the total fatty acid composition was found among mouseand soil-derived strains in this study. We showed that there were differences in the composition of many FAs, including the LPS indicator (C 14:0 3-OH FA), and differences in biofilm formation and flagella between the mouse-and soil-derived strains.…”

Bilayer Properties of Lipid A from Various Gram-Negative Bacteria

“…Burkholderia pseudomallei is related to the outbreak of melioidosis, a contagious disease mainly found in tropical regions; recently, however, melioidosis has been spreading globally. The structure of B. pseudomallei lipid A has the same number of chains and length as B. cepacia, but 4-amino-4-deoxy-L-arabinose (Ara4N) is linked to the 1-phosphate group (12). In this study, lipid A from B. cepacia and B. pseudomallei are denoted as BC-A and BC-B, respectively.…”

“…S1). Four primary acyl chains are linked to sugar backbone in 2-, 3-, 2 0 -, and 3 0 -positions, and two secondary acyl chains are esterified to the hydroxyl groups of the 2 0 -, and 3 0 -primary acyl chains, i.e., C2 C 14 (3-OH), C3 C 14 (3-OH), C2 0 C 14 (3-OH) and a secondary ester-linked C 12 , and the C3 0 C 14 (3-OH) and a secondary ester-linked C 14 (17). In this study, E. coli lipid A is denoted as EC-A.…”

“…V. cholerae lipid A consists of the standard headgroup and six acyl chains. Four primary acyl chains are linked to the 2-, 3-, 2 0 -, and 3 0 -positions, and two secondary acyl chains are linked to the 2 0 -and 3 0 -primary acyl chains, i.e., C2 C 14 (3-OH); C3 C 12 (3-OH); C2 0 C 14 (3-OH) and a secondary ester-linked C 14 ; and C3 0 C 12 (3-OH) and a secondary ester-linked C 12 (Fig. S1), which is denoted as VC-A.…”

“…i.e., the C2 position contains a primary amide-linked C 14 (3-OH, meaning a hydroxyl group attached to the C 3 position) and a secondary ester-linked C 12 ; the C3 position contains a primary ester-linked C 12 (3-OH); the C-2 0 position contains a primary amide-linked C 14 (3-OH) and a secondary ester-linked C 12 (2-OH); and the C3 0 position contains a primary esterlinked C 12 (3-OH) and a secondary ester-linked C 12 . In hexa-acylated lipid A, a secondary acyl chain at the 2-primary acyl chain is missing.…”