27.1 Prоkаryоtic Diversity A Brief Histоry of Microbiology: Microbiology hаs а fascinating history that has unfolded over centuries, marked by groundbreaking discoveries and advancements in the understanding of the microscopic world. The journey of microbiology can be traced back to the 17th century when pioneers like Antonie van Leeuwenhoek, equipped with simple microscopes, first observed and documented microorganisms. His meticulous observations opened a new realm, revealing a hidden world of tiny life forms that were previously unseen. The 19th century witnessed a paradigm shift with the development of the germ theory of disease. Louis Pasteur, through his experiments, demonstrated that microorganisms were responsible for fermentation and spoilage. Robert Koch, building on Pasteur's work, formulated a set of postulates that linked specific microorganisms to particular diseases, laying the foundation for the germ theory. This groundbreaking concept revolutionized medicine and public health, paving the way for the development of vaccines and antimicrobial treatments. The 20th century brought further milestones, including the discovery of antibiotics like penicillin by Alexander Fleming. This ushered in the era of antimicrobial therapy, transforming the landscape of medicine. Advances in molecular biology and genetics during the latter half of the century provided deeper insights into the structure and function of microorganisms, unraveling the mysteries of their genetic codes and cellular processes. germ-theory_orig.jpg
Clаssifying prоkаryоtesEаrly classificatiоn characteristicsEarly taxonomies for classifying prokaryotes relied on readily observable or microscopically detectable differences between organisms or groups of organisms. Key characteristics initially used to classify prokaryotes were:1. photosynthetic ability2. cell wall structure3. motility4. unicellular or colony-forming or filamentous5. spore-forming ability6. pathogenicityMolecular approaches to classificationAs technologies have advanced, various approaches have been used to create taxonomies. For example, information from genomics can be combined with phenotypic and phylogenetic data to create more meaningful and well-informed classifications. Molecular approaches include the following:1. the analysis of the amino acid sequences of key proteins2. the analysis of nucleic acid-base sequences by establishing the percent of guanine and cytosine3. nucleic acid hybridization, which is essentially the mixing of single-stranded DNA from two species and determination of the amount of base-pairing (closely related species will have more bases pairing)4. gene and RNA sequencing, especially looking at ribosomal DNA sequences (rDNA)5. whole-genome sequencingThe three-domain system of phylogeny, originated by Carl Woese, relies on all of these molecular methods but emphasizes the comparison of rDNA sequences to establish the evolutionary relatedness of all organisms. The rDNA sequences were chosen for their high degree of evolutionary conservation to ask questions about these most ancient splits in the tree of life.