Q.66 Which one of the following is the most appropriate technique to determine the relatedness of two
bacterial species?
(A) DNA hybridization
(B) Doubling time measurement
(C) Biochemical characterization
(D) Plasmid profiling

Discover the most accurate method for assessing bacterial species relatedness, with DNA hybridization as the gold standard in microbial taxonomy.

DNA hybridization stands out as the most precise method to measure genetic similarity between bacterial species, widely used in taxonomy since the 1960s. This technique directly compares whole-genome DNA sequences to quantify relatedness, setting it apart from phenotypic approaches. For students preparing for exams in molecular biology or microbiology, understanding its superiority clarifies key concepts in bacterial classification.​

Correct Answer

(A) DNA hybridization

This option is correct because DNA-DNA hybridization (DDH) measures the degree of reassociation between denatured DNA strands from two bacteria, providing a quantitative genomic similarity value—typically, strains with over 70% hybridization belong to the same species. Modern variants like microarray-based DDH enhance throughput while maintaining accuracy for species delineation.​

Option Explanations

DNA Hybridization

DNA hybridization involves denaturing genomic DNA from two strains, allowing complementary strands to reanneal, and measuring reassociation stability via melting temperature or percentage similarity. It correlates closely with genome sequence identity (e.g., average nucleotide identity, ANI), making it the cornerstone for bacterial species definition.​

Doubling Time Measurement

Doubling time assesses growth rate under specific conditions but reflects physiological responses, not genetic relatedness—different species can have similar rates due to environmental adaptation.​

Biochemical Characterization

This phenotypic method tests metabolic traits like enzyme activity or substrate use (e.g., API strips) but often fails for closely related species with convergent evolution, lacking genomic precision.​

Plasmid Profiling

Plasmid profiling examines extrachromosomal DNA size and number via electrophoresis but varies due to horizontal transfer, making it unreliable for core genomic relatedness assessment.​

Why It Matters for Exams

In competitive exams like CSIR NET or university tests, DNA hybridization distinguishes genotypic from phenotypic methods, emphasizing its role in resolving ambiguities in 16S rRNA sequencing. Mastery of these options boosts scores in microbiology sections focused on bacterial taxonomy.