Final answer:
The 16S rRNA is the most useful for bacterial identification as its sequences are highly conserved across various bacterial species, providing a reliable marker for identification and classification. The 18S and 28S rRNA are factors in eukaryotes, and the 5S rRNA is not information-rich enough for bacterial identification.
Step-by-step explanation:
Identification of Bacteria Using rRNA
The 16S rRNA is most useful for bacterial identification. The 16S rRNA gene is found in the small subunit of prokaryotic ribosomes, and its sequences are highly conserved among different species of bacteria, making it an excellent marker for identifying and classifying bacteria. This is because the 16S rRNA has regions that are highly conserved mixed with regions that vary among different bacterial species, allowing for both the establishment of bacterial phylogeny and the identification of bacterial species. In contrast, the 18S and 28S rRNA are found in eukaryotes, and the 5S rRNA is too short to provide sufficient information for bacterial identification.
It is important to note that the 16S rRNA gene's usefulness extends to studies related to evolutionary relationships among bacteria and is often used in phylogenetic studies. A classic example is the determination of bacterial species from historical samples, which can provide valuable insights into epidemics from the past by comparing the 16S rRNA sequence to modern strains, as mentioned with bacterium pestis from the 14th century.