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Category: Bacterial Pathogenesis
Phase Variation in Legionella pneumophila Serogroup 1, Subgroup OLDA, Strain RC1 Influences Lipid A Structure, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555817985/9781555812300_Chap14-1.gif /docserver/preview/fulltext/10.1128/9781555817985/9781555812300_Chap14-2.gifAbstract:
A change in the lipopolysaccharide (LPS) upon phase variation in Legionella pneumophila serogroup 1, subgroup OLDA, wild-type strain RC1 was detected with the aid of LPS-specific monoclonal antibody MAb 2625. Chromosomal insertion and excision of a 30-kb instable genetic element of possibly phage origin was identified as the molecular mechanism for phase variation. The core of the LPS is a nonasaccharide that lacks heptose and phosphate, contains abundant 6-deoxy sugars, and is highly O- and N-acetylated. The MAb 2625 epitope is present in wild-type RC1 cells and is lost in the spontaneous mutant 811 upon phase variation. Lipid A was prepared by mild acid hydrolysis (0.1 M NaOAc-HOAc buffer, pH 4.4,100№C, 4 h) of LPS each of wild-type RC1 and phase-variant 811 followed by centrifugation and lyophilization of the pellet. LPS biosynthesis pathways involved in assembly of lipid A were also affected by phase variation, which resulted in a specifically altered lipid A structure with a modified profile of fatty acids of a particular type. Phase variation may affect a regulatory factor, which influences LPS biosynthesis, virulence, and serum resistance.
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Parts of negative ion mode MALDI-TOF mass spectra of tetraacyl lipid A from L. pneumophila serogroup 1, subgroup OLDA, wild-type RC1 (top panel) and phase-variant 811 (bottom panel). Tetraacyl monophos-phoryl lipid A was prepared by de-O-acylation with hydrazine; one of the phosphate groups (most likely at position 1) was split, probably due to overheating during work-up of the reaction mixture with acetone. The m/z value for [M-H]− ions, the calculated chemical molecular mass (in parentheses), and the deduced chain length (the total number of carbons) of the 3−hydroxylated fatty acids at positions 2 and 2′ are given for each major ion peak of tetraacyl lipid A with one residue each of 14:0(3-OH) and 14:0(2,3-di-OH) at positions 3 and 3′. The mass spectra were acquired in reflector configuration with 2,5-dihydroxybenzoic acid as matrix.
Parts of negative ion mode MALDI-TOF mass spectra of tetraacyl lipid A from L. pneumophila serogroup 1, subgroup OLDA, wild-type RC1 (top panel) and phase-variant 811 (bottom panel). Tetraacyl monophos-phoryl lipid A was prepared by de-O-acylation with hydrazine; one of the phosphate groups (most likely at position 1) was split, probably due to overheating during work-up of the reaction mixture with acetone. The m/z value for [M-H]− ions, the calculated chemical molecular mass (in parentheses), and the deduced chain length (the total number of carbons) of the 3−hydroxylated fatty acids at positions 2 and 2′ are given for each major ion peak of tetraacyl lipid A with one residue each of 14:0(3-OH) and 14:0(2,3-di-OH) at positions 3 and 3′. The mass spectra were acquired in reflector configuration with 2,5-dihydroxybenzoic acid as matrix.
Proposed structure of the major lipid A from L. pneumophila serogroup 1, subgroup OLD A, wild-type RC1, and phase-variant 811. The position of the fatty acids is shown according to published data ( 11 ). The chain length of the 3-hydroxylated fatty acids at positions 2 and 2′ is indicated as the total number of carbons n = 20 at both GlcN3N residues in wild-type RC1. In the avirulent phase variant 811, the chain length of the 3-hydroxylated fatty acids at positions 2 and 2′ is n = 16 at one and n = 18 at the other GlcN3N residue.
Proposed structure of the major lipid A from L. pneumophila serogroup 1, subgroup OLD A, wild-type RC1, and phase-variant 811. The position of the fatty acids is shown according to published data ( 11 ). The chain length of the 3-hydroxylated fatty acids at positions 2 and 2′ is indicated as the total number of carbons n = 20 at both GlcN3N residues in wild-type RC1. In the avirulent phase variant 811, the chain length of the 3-hydroxylated fatty acids at positions 2 and 2′ is n = 16 at one and n = 18 at the other GlcN3N residue.
Fatty acid composition of lipid A from wild-type RC1 and phase-variant 811 a
Fatty acid composition of lipid A from wild-type RC1 and phase-variant 811 a