Evolution of the Kdo2-lipid A biosynthesis in bacteria

Area of Science:

• Microbiology
• Evolutionary Biology
• Biochemistry

Background:

• Lipid A is the endotoxic component of lipopolysaccharide (LPS) in Gram-negative bacteria.
• It anchors LPS in the outer membrane and triggers host immune responses, potentially causing sepsis.
• The biosynthesis of Kdo2-lipid A, an LPS substructure, involves a nine-enzyme pathway.

Purpose of the Study:

• To investigate the evolutionary history of the Kdo2-lipid A biosynthetic pathway.
• To understand the distribution of genes encoding the nine enzymes across diverse bacterial species.

Main Methods:

• Comparative genomics analysis of genes encoding Kdo2-lipid A biosynthetic enzymes.
• Examination of gene distribution across various bacterial phyla, with a focus on Proteobacteria.

Main Results:

• Not all Gram-negative bacteria possess all nine enzymes for Kdo2-lipid A synthesis.
• Some bacteria lack these genes entirely, while others have only the initial four (LpxA, LpxC, LpxD, LpxB).
• Five enzymes originated from three independent gene duplications, particularly within Proteobacteria, leading to pathway optimization.

Conclusions:

• The nine-enzyme pathway, prevalent in Escherichia coli and related Proteobacteria, represents a highly derived and optimized form.
• Simpler pathways exist in other bacterial groups, producing Kdo2-lipid A variants.
• The Kdo2-lipid A pathway illustrates the remarkable genomic plasticity and adaptive evolution in bacteria, especially Proteobacteria.