Evolution of the Kdo2-lipid A biosynthesis in bacteria

<p>Abstract</p> <p>Background</p> <p>Lipid A is the highly immunoreactive endotoxic center of lipopolysaccharide (LPS). It anchors the LPS into the outer membrane of most Gram-negative bacteria. Lipid A can be recognized by animal cells, triggers defense-related responses, and causes Gram-negative sepsis. The biosynthesis of Kdo₂-lipid A, the LPS substructure, involves with nine enzymatic steps.</p> <p>Results</p> <p>In order to elucidate the evolutionary pathway of Kdo₂-lipid A biosynthesis, we examined the distribution of genes encoding the nine enzymes across bacteria. We found that not all Gram-negative bacteria have all nine enzymes. Some Gram-negative bacteria have no genes encoding these enzymes and others have genes only for the first four enzymes (LpxA, LpxC, LpxD, and LpxB). Among the nine enzymes, five appeared to have arisen from three independent gene duplication events. Two of such events happened within the Proteobacteria lineage, followed by functional specialization of the duplicated genes and pathway optimization in these bacteria.</p> <p>Conclusions</p> <p>The nine-enzyme pathway, which was established based on the studies mainly in <it>Escherichia coli </it>K12, appears to be the most derived and optimized form. It is found only in <it>E. coli </it>and related Proteobacteria. Simpler and probably less efficient pathways are found in other bacterial groups, with Kdo₂-lipid A variants as the likely end products. The Kdo₂-lipid A biosynthetic pathway exemplifies extremely plastic evolution of bacterial genomes, especially those of Proteobacteria, and how these mainly pathogenic bacteria have adapted to their environment.</p

Quantitative Demonstration of Cell Surface Involvement in a Plant-Animal Symbiosis: Lectin Inhibition of Reassociation

The freshwater hydra, Hydra viridis is normally associated with Chlorella-like, algal symbionts which inhabit the host\u27s digestive cells. Under experimental conditions bleached hydra will reassociate with algae harvested from green hydra, but not from our cultures of wild type Chlorella or strain NC64A which when originally isolated from Paramecium bursaria was symbiotically competent. Because of its demonstrated selectivity, the reassociation process is hypothesized to involve a recognition interface whose active participants are the algae cell wall and the digestive cell membrane. The data presented here confirm the hypothesis and suggest some potential molecular characteristics of the interacting partners. Concanavalin A (Con A), a plant lectin, used widely for similar studies in other systems totally inhibits reassociation; Wheat Germ Agglutinin (WGA), ricin and Lens culinaris lectin do so to a lesser degree. These results are consistent with the hypothesis that glycoproteins on the cells\u27 peripheries are involved in cell-cell recognition in this system

RECOGNITION OF SYMBIOTIC ALGAE BY HYDRA VIRIDIS. A QUANTITATIVE STUDY OF THE UPTAKE OF LIVING ALGAE BY APOSYMBIOTIC H. VIRIDIS

Volume: 145Start Page: 565End Page: 57

METABOLIC RELATIONSHIPS BETWEEN GREEN HYDRA AND ITS SYMBIOTIC ALGAE

Volume: 153Start Page: 228End Page: 23

Evolution of the Kdo\u3csub\u3e2\u3c/sub\u3e-lipid A Biosynthesis in Bacteria

Background: Lipid A is the highly immunoreactive endotoxic center of lipopolysaccharide (LPS). It anchors the LPS into the outer membrane of most Gram-negative bacteria. Lipid A can be recognized by animal cells, triggers defense-related responses, and causes Gram-negative sepsis. The biosynthesis of Kdo2-lipid A, the LPS substructure, involves with nine enzymatic steps. Results: In order to elucidate the evolutionary pathway of Kdo2-lipid A biosynthesis, we examined the distribution of genes encoding the nine enzymes across bacteria. We found that not all Gram-negative bacteria have all nine enzymes. Some Gram-negative bacteria have no genes encoding these enzymes and others have genes only for the first four enzymes (LpxA, LpxC, LpxD, and LpxB). Among the nine enzymes, five appeared to have arisen from three independent gene duplication events. Two of such events happened within the Proteobacteria lineage, followed by functional specialization of the duplicated genes and pathway optimization in these bacteria. Conclusions: The nine-enzyme pathway, which was established based on the studies mainly in Escherichia coli K12, appears to be the most derived and optimized form. It is found only in E. coli and related Proteobacteria. Simpler and probably less efficient pathways are found in other bacterial groups, with Kdo2-lipid A variants as the likely end products. The Kdo2-lipid A biosynthetic pathway exemplifies extremely plastic evolution of bacterial genomes, especially those of Proteobacteria, and how these mainly pathogenic bacteria have adapted to their environment