This uncertainty resulted from the lack of distinctive structures in most bacteria, as well as lateral gene transfer that occurred between unrelated species. While these schemes previously allowed the identification and classification of bacterial strains, it was long unclear whether these differences represented variation between distinct species or between strains of the same species. Bacteria can be classified on the basis of cell structure, cellular metabolism, or by differences in cell components such as DNA, fatty acids, pigments, antigens, and quinones.
viable but nonculturable: Viable but nonculturable (VBNC) bacteria refers to bacteria that are in a state of very low metabolic activity and do not divide, but are alive and have the ability to become culturable once resuscitated.Ĭlassification seeks to describe the diversity of bacterial species by naming and grouping organisms based on similarities.Recent advances in molecular technique are allowing uncultured bacteria to be classified.If a bacterium cannot be cultured, it is hard to study it to find commonalities and differences from other species of bacteria.
Classification is the attempt to identify and group different species of bacteria together by common traits. It should be noted that Bacteria and Archaea are similar physically, but have different ancestral origins as determined by DNA of the genomes that encode different prokaryotes. The archaea and eukaryotes are more closely related to each other than either is to the bacteria. However, molecular systematics show prokaryotic life to consist of two separate domains, originally called Eubacteria and Archaebacteria, but now called Bacteria and Archaea that evolved independently from an ancient common ancestor. The term "bacteria" was traditionally applied to all microscopic, single-cell prokaryotes, having the similar traits outlined above. Small size is extremely important because it allows for a large surface area-to-volume ratio which allows for rapid uptake and intracellular distribution of nutrients and excretion of wastes. For example, Escherichia coli cells, an "average" sized bacterium, are about 2 micrometres (μm) long and 0.5 μm in diameter. Perhaps the most obvious structural characteristic of bacteria is (with some exceptions) their small size. These subcellular compartments have been called "bacterial hyperstructures".īinary fission: Many bacteria reproduce through binary fission. Bacteria were once seen as simple bags of cytoplasm, but elements such as prokaryotic cytoskeleton, and the localization of proteins to specific locations within the cytoplasm have been found to show levels of complexity. They consequently lack a true nucleus, mitochondria, chloroplasts, and the other organelles present in eukaryotic cells, such as the Golgi apparatus and endoplasmic reticulum. Unicellularity and thus division by binary-fissionīacteria do not tend to have membrane-bound organelles in their cytoplasm and thus contain few large intracellular structures. In addition, they grow in organic matter and the live bodies of plants and animals, providing outstanding examples of mutualism in the digestive tracts of humans, termites, and cockroaches.īut what defines a bacteria? Bacteria as prokaryotes share many common features, such as: Bacteria grow in soil, acidic hot springs, radioactive waste, water, and deep in the Earth's crust. Bacteria were among the first life forms to appear on Earth, and are present in most habitats on the planet. binary fission: a form of asexual reproduction and cell division used by all prokaryotes, (bacteria and archaebacteria)īacteria constitute a large domain of prokaryotic microorganisms. archaea: a taxonomic domain of single-celled organisms lacking nuclei, formerly called archaebacteria but now known to differ fundamentally from bacteria. Not all prokaryotes are bacteria, some are archaea, which although they share common physicals features to bacteria, are ancestrally different from bacteria. There are three notable common traits of bacteria, 1) lack of membrane-bound organelles, 2) unicellular and 3) small (usually microscopic) size. 
Bacterial species are typified by their diversity. Bacteria vary from species to species, thus assigning many common traits to bacteria is difficult.
0 kommentar(er)
