Contrasting patterns of evolutionary divergence within the Acinetobacter calcoaceticus pca operon

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Acinetobacter calcoaceticus utilizes protocatechuate and catechol through distinct metabolic pathways.
• The enzymes for protocatechuate catabolism are encoded by pca genes, while catechol dissimilation involves cat genes.
• Previous studies identified some pca and cat genes, but the complete organization and evolutionary relationship remained unclear.

Purpose of the Study:

• To elucidate the complete genetic organization of the pca operon in Acinetobacter calcoaceticus.
• To compare the nucleotide sequences of pca genes with their analogous cat genes.
• To investigate the evolutionary relationships and potential DNA exchange between pca and cat gene regions.

Main Methods:

• Nucleotide sequencing of pcaIJFB and pcaK genes.
• Comparative analysis of nucleotide sequences between pca and cat gene regions.
• Analysis of G+C content and codon usage patterns.

Main Results:

• The complete pca structural genes are organized in a single operon: pcaIJFBDKCHG.
• The pcaIJF region shares high sequence identity with the catIDJF region, indicating potential DNA exchange.
• The pcaD, pcaC, pcaH, and pcaG genes show substantial divergence from their cat counterparts.
• The pcaK gene has no known cat counterpart, and its sequence suggests a transmembrane transport function.

Conclusions:

• The pca genes in Acinetobacter calcoaceticus form a single, tightly clustered operon.
• Sequence conservation in the pcaIJF region may result from DNA sequence information exchange with the catIJF region.
• Divergence in other pca genes reflects evolutionary adaptation specific to Acinetobacter calcoaceticus.
• The novel pcaK gene likely encodes a transmembrane protein involved in substrate transport.