Systematics Lecture PDF

Taxonomy/Systematics The science for studying classification is called Taxonomy (Greek: taxis = arrangement; nomos = law) AND is further divided into three working groups: Classification, Identification and Nomenclature. Classification : placing organisms within groups with members exhibiting simila...

Taxonomy/Systematics The science for studying classification is called Taxonomy (Greek: taxis = arrangement; nomos = law) AND is further divided into three working groups: Classification, Identification and Nomenclature. Classification : placing organisms within groups with members exhibiting similarities (structure, physiological or evolutionary relatedness). These groups are termed as taxa (s. taxon) Nomenclature is assigning of scientific names to taxonomic groups in accordance with accepted rules. The term systematics sometimes is referred synonymously with taxonomy. While, taxonomy is plainly referred to identification, classification and naming of organisms; systematics is the evolutionary history of organisms through time. Some important facts about microorganisms are that: The presence of microbes is ubiquitous Most of the microbes are harmless to us. Instead, they help us by secreting various economically useful metabolites. They keep the biosphere running by performing biodegradation and cycles of carbon, nitrogen, oxygen, sulfur, etc. Microorganisms can also harm humans. They cause diseases in plants as well as animals and food spoilage.  The importance of taxonomy has been ever increasing. In 2000, a project called “All Species Inventory” was started (http://www.all-species.org/). Aim : to identify and record every species of life by 2025. Very challenging; till now 1.5 million species- identified Estimated mumber of species: between 7 to 100 million. For This mind boggling number : important of cataloguing the species in a proper and scientific way. Thus taxonomy is important for (i) effective communication among scientists about the identity of a particular microbe (ii) catalogue a large number of species in a systematic manner, (iii) help in predictions and further research about a particular isolate if little is known about it and it shows some similarities with microbes of particular group  2. Binomial nomenclature For millions of organisms, common names - lead to misunderstanding as different names are used for same organism in different places. a naming system –introduced : termed “scientific nomenclature”. Every organism is given a binomial latin name first described by Carolus Linnaeus. The first part : genus which is followed by species. For example; humans are assigned scientific name as Homo sapiens. alwaysitalicized (Homo sapiens), where genus name starts with a capital letter. Abbreviated as H. Sapiens  Rank Example of taxonomic hierarchy Domain Eukarya Kingdom Fungi Phylum Ascomycota Class Hemiascomycetes Order Saccharomycetales Family Saccharomycetaceae Genus Saccharomyces Species cerevisiae Two kingdom classification Three kingdom classification Ernst H. Haeckel in 1866 proposed a three-kingdom classification with a new kingdom – Protista  Carl Woese and George Fox (1977)three kingdom classification: based on 16s/18srRNA sequencing Carl Woese et al. introduced a new taxon – domain above the level of kingdom in their new system of classification, in 1990. Under this system, life has been divided into three domains, the Bacteria, the Archaea and the Eukarya. Exception: linear choromosomes found in Borrelia burgdorferi (lyme dis), Sterptomyces lividans, S. Coelicolor, Rhodococcus fascians. A. tumefaciens: one ln and one circular genome. Linear plasmids in bacteria: S. rochei, Nocardia opaca, Thiobacillus versutus  DNA Polymerases in prok. I, II, III, IV, V In eukaryotes: alpha, delta, epsilon, gamma Prokaryotes: no introns in genome Transcription and translation are coupled Polycistronic mRNA