Was the Last Bacterial Common Ancestor a Monoderm after All?

Area of Science:

• Microbiology
• Evolutionary Biology
• Genomics

Background:

• Understanding the cell wall of the last bacterial common ancestor (LBCA) is crucial for deciphering early life evolution.
• Phylogenomics has advanced bacterial phyla relationships but left questions about the outer membrane evolution in diderm (Gram-negative) bacteria.
• The transition between monoderm (Gram-positive) and diderm bacteria and associated peptidoglycan changes need clarification.

Purpose of the Study:

• To infer the cell-wall architecture of the LBCA using phylogenomic analysis and literature review.
• To investigate the evolution of the division and cell-wall synthesis (dcw) gene cluster.
• To determine the phylogenetic distribution of genes involved in the outer membrane biosynthesis of diderm bacteria.

Main Methods:

• Bayesian ancestral state reconstruction based on a phylogenomic tree of cultivated bacteria.
• Literature review of bacterial cell-wall characteristics.
• Homology- and model-based methods for analyzing the dcw gene cluster.
• Extensive similarity searches for outer membrane biosynthesis genes.

Main Results:

• Phylogenomic analyses suggest the LBCA possessed a monoderm cell-wall architecture.
• The appearance of the outer membrane in diderm bacteria may not have been a unique event, but rather a repeated evolutionary adaptation.
• The study identified the phylogenetic distribution of genes related to outer membrane biosynthesis.

Conclusions:

• The LBCA likely had a monoderm cell wall, implying multiple independent evolutions of the diderm structure.
• Selective pressures may have driven the repeated acquisition of the outer membrane.
• Future studies with broader phenotypic data may refine these conclusions.