(A) G+C content

(B) 23S rRNA sequences

(C) tRNA sequences

(D) 16S rRNA sequences

Phylum Proteobacteria divides into α-, β-, γ-, δ-, and ε-classes based on genetic analysis for bacterial taxonomy. The correct answer is (D) 16S rRNA sequences.​

Correct Answer

Phylum Proteobacteria subdivides into α-, β-, γ-, δ-, and ε-proteobacteria based on (D) 16S rRNA sequences. Carl Woese established this system in the 1980s using 16S ribosomal RNA gene sequences to reveal evolutionary relationships among Gram-negative bacteria.​

Option Analysis

• (A) G+C content: Incorrect; G+C base composition defines some bacterial groups but fails to capture Proteobacteria’s phylogenetic diversity across classes.​

• (B) 23S rRNA sequences: Incorrect; while useful for phylogeny, 16S rRNA serves as the standard due to its conserved and variable regions ideal for universal bacterial classification.​

• (C) tRNA sequences: Incorrect; tRNA offers limited resolution for higher-level taxonomy compared to rRNA’s robust phylogenetic signal.​

• (D) 16S rRNA sequences: Correct; this marker gene’s sequence homology groups Proteobacteria into classes reflecting shared ancestry, aiding identification in microbiology and biotechnology.​

Class Overview

Proteobacteria, the largest bacterial phylum, includes diverse microbes from soil symbionts to pathogens, relevant to microbial fermentation and genetics.

• Alphaproteobacteria: Nitrogen-fixing Rhizobium, photosynthetic purple nonsulfur bacteria.​

• Betaproteobacteria: Nitrifiers like Nitrosomonas, human microbiota members.​

• Gammaproteobacteria: E. coli, Vibrio cholerae; dominant in ocean and gut microbiomes.​

• Deltaproteobacteria: Sulfate-reducers, predatory Bdellovibrio.​

• Epsilonproteobacteria: Helicobacter pylori, Campylobacter; gastric pathogens.​

This classification supports biochemical assays and molecular biology in biotechnology research.