Bergey’s Manual of Systematic Bacteriology groups bacteria into species according to phylogenetic relationships.

Question Breakdown

This GATE Life Sciences question tests bacterial taxonomy evolution. Early editions used phenotypic traits; modern Systematic Bacteriology (2nd/3rd ed.) employs 16S rRNA sequencing, DNA G+C content, and multi-locus sequence typing for evolutionary relatedness.

Option Analysis

(A) Nutritional requirement

Phenotypic trait used in Determinative Bacteriology (identification keys), not species delineation in Systematic edition.​

(B) Phylogenetic relationships

Correct. Modern classification: phyla → classes → orders → families → genera → species based on rRNA phylogeny, ANI (>95-96%), dDDH (>70%).​

(C) Pathogenic properties

Clinical grouping (e.g., Enterobacteriaceae); scatters pathogens across phylogenetic groups (Salmonella in Gammaproteobacteria).​

(D) Morphology

Early phenetic classification (shape, Gram stain); insufficient for species due to convergence (cocci in multiple phyla).​

Correct Choice

(B) Phylogenetic relationships

Bergey’s Manual groups bacteria species using phylogenetic relationships via 16S rRNA, replacing morphology-based systems for accurate taxonomy.​

Classification Evolution

1st ed. (1923-89): Phenetic (morphology, physiology)
9th ed. Determinative (1994): ID keys
2nd ed. Systematic (1984-2012): 5 volumes by phylum
3rd ed. (2023+): Digital, MLST integration

Volume organization:

• Vol 1: Archaeal domains

• Vol 2: Proteobacteria

• Vol 3: Firmicutes (Bacilli, Clostridia)

• Vol 4: Bacteroidetes, Spirochaetes

• Vol 5: Actinobacteria

Criteria Comparison

GATE Exam Relevance

Microbiology PYQ tests taxonomy paradigm shift. Key: Systematic = phylogeny (rRNA), Determinative = phenotype (biochemical tests). Species definition: 70% dDDH + 97% 16S similarity + phenotypic coherence.​