Q.11

Sequence comparison of which of the following genes is used as a measure of

evolutionary divergence across bacterial species?

(A) pbpG

(B) slyD

(C) 16S rRNA

(D) 18S rRNA

16S rRNA gene sequence comparison serves as the standard measure for assessing evolutionary divergence across bacterial species.

Correct Answer

C) 16S rRNA
The 16S rRNA gene is the primary molecular marker for bacterial taxonomy and phylogeny due to its conserved regions for universal priming and variable regions reflecting evolutionary divergence. Sequence identity thresholds, such as >98.7% for species delineation, enable precise measurement of genetic distances across bacterial species.

Option Explanations

pbpG

pbpG encodes penicillin-binding protein 7 in bacteria like E. coli, involved in cell wall peptidoglycan maintenance rather than conserved phylogenetic markers. It shows high variability and is not used for broad evolutionary divergence studies across species.

slyD

slyD codes for a FK506-binding protein (FKBP) peptidyl-prolyl isomerase in E. coli and other bacteria, functioning in protein folding, metal chaperoning, and stress responses. Mutational analyses reveal phenotypes like growth defects but no role in standard bacterial phylogeny or divergence metrics.

16S rRNA

This ribosomal RNA gene (~1,500 bp) evolves slowly with nine variable regions amid conserved domains, ideal for PCR amplification and alignment in phylogenetic trees. It underpins bacterial classification, revealing divergence via pairwise sequence distances, though limited below species level due to stasis and HGT.

18S rRNA

18S rRNA is the eukaryotic small subunit ribosomal RNA counterpart, used for fungal or protist phylogeny, not bacteria which lack nuclei and use 16S rRNA. Its sequence diverges faster in eukaryotes, making it irrelevant for bacterial evolutionary comparisons.