GENERAL MICROBIOLOGY - T.P. Pirog - 2004

7. SYSTEMATICS OF PROKARYOTES

7.6. MODERN TRENDS IN BACTERIAL SYSTEMATICS

7.6.1. Phenotypic systematics

Over the century-long history of MICROBIOLOGY AS A science, phenotypic bacterial systematics has gradually emerged. A combination of morphological, cultural, and physiological characteristics serves as the criterion for grouping organisms into taxa of various ranks. This approach forms The basis of modern bacterial manuals (Bergey's Manuals, 8th and 9th editions). Are these existing manuals satisfactory? Unfortunately, they are far from being always satisfactory, for several reasons:

1. One of the debatable issues in phenotypic systematics is what should form the basis of bacterial Classification: Cell Morphology or cellular METABOLISM? This raises a fundamental question: is there a correlation between morphological and physiological traits? Research into the phenotypic properties of Bacteria conducted in the 1970s by G.A. Zavarzin led to the Conclusion that no such correlation exists, and morphological and physiological commonality cannot be considered a universal law.

2. The manuals summarize qualitatively and quantitatively disparate information accumulated by microbiologists over 100 years, resulting in a lack of uniform classification criteria for different groups of microorganisms.

3. Establishing criteria for defining taxonomic ranks remains problematic in bacteriology. The same features may be diagnostic for a species in one case, and for a genus in another. In fact, systematic theory currently lacks a Quantitative evaluation of taxonomic rank.

4. Bacterial manuals traditionally rely on variable traits (for example, a trait being positive in 10–80% of a studied species). What causes such Variability? Either the strains under investigation were studied under inadequate conditions, non-standard Methods were used in the experiments, or mutant forms were included in the analysis. The ability of Plasmids to serve as an additional source of genetic material undoubtedly contributes to microbial variability. In this context, is it appropriate to use a trait like Antibiotic Resistance if it can be plasmid-encoded and is therefore unstable? Clearly, classification should rely on stable traits encoded by chromosomal genes.

5. THE CONCEPT OF the "type" taxon has become obsolete. The major pitfall in using type strains is that they do not necessarily represent the truly most typical elements of their taxa.