Bacteriologia

Bacteriology
Michael T Madigan, Southern Illinois University, Carbondale, Illinois, USA Deborah O Jung, Southern Illinois University, Carbondale, Illinois, USA
Bacteriology is the study of bacteria, small cells that live an independent existence and play key roles in the biosphere. Bacteria include all prokaryotic cells and comprise two major phylogenetic lineages, Bacteria and Archaea.Bacteriology played a major role in the development of molecular genetics, and bacteria have been excellent tools for basic and applied research. In recent years, bacteria have been harnessed to produce valuable commercial products, and the critical contributions of prokaryotes to the functioning of the biosphere have been revealed.

Introductory article
Article Contents
. Modern Concepts ofProkaryotic Phylogeny and Systematics . The Chimaeric Nature of the Eukaryotic Cell . Morphological and Physiological Diversity of Prokaryotes . Trends in Microbiology: From Medical to General to Molecular Microbiology . Influence of Bacteriology on Genetics and Molecular Biology . Prokaryotes in Science: Medicine, Biotechnology and Evolutionary Research . Authentic and Genetically Engineered Prokaryotesin Basic and Applied Science

Modern Concepts of Prokaryotic Phylogeny and Systematics
Bacteriology is the study of bacteria, a large and diverse group of microscopic organisms that exist as single cells or cell clusters. Bacteria are a major class of microorganisms, which also include protists (microbial eukaryotes) and viruses, the latter of which are microscopic but not cellular. Bacteriaare first and foremost cells, and as such, show all the properties of living systems. These include metabolism, reproduction (growth), differentiation, communication, movement and evolution. Examination of the internal structure of cells reveals two patterns, prokaryotic and eukaryotic (Figure 1). Eukaryotic cells are typically larger and structurally more complex than prokaryotic cells. Microbialeukaryotic cells include the algae, fungi and protozoa. In contrast to eukaryotic cells, bacteria are prokaryotic cells and have a simpler internal structure, lacking membrane-enclosed organelles such as a nucleus, mitochondria and chloroplasts (Figure 1). With rare exception, the deoxyribonucleic acid (DNA) of prokaryotic cells is arranged in a single circular molecule called the nucleoid. Thisstructure is twisted and contorted in such a way as to fit inside the very limited cell volume available in a prokaryotic cell. A typical rod-shaped prokaryote such as the intestinal bacterium Escherichia coli has dimensions of 1 Â 2 mm and a cell volume of about 2 mm3. Despite this small size, all cellular components necessary for life, including a cell wall, cytoplasmic membrane, ribosomes, cytoplasmand nucleoid (which in E. coli, contains 4.68 million base pairs of DNA) (Figure 1) are contained within the cell structure. Since microbial cells have left relatively few visible clues to their phylogenetic (evolutionary) backgrounds, analyses of their genes are necessary to derive phylogenetic (evolutionary) relationships. The most insightful of these analyses has been the comparativesequencing of ribosomal ribonucleic acid (rRNA), a major class of RNA that plays both structural and catalytic roles in ribosomes, the cell’s

. The Importance of Prokaryotes for Maintaining a Sustainable Biosphere

doi: 10.1002/9780470015902.a0000449

protein synthesis factories. Methods for sequencing and analysing genes encoding rRNA are now routine. From sequence analyses, computer algorithms canconstruct trees that depict the phylogenetic history of the selected organisms. The results of comparative ribosomal RNA gene sequencing show that three phylogenetic domains of cells exist. Two domains of prokaryotes are known: the Bacteria and the Archaea. The third domain of life, the Eukarya, includes all eukaryotic cells. (Since these domain names are formally considered the highest rank...