[Infectiology] Basic taxonomy

Infectiology

Taxonomy is the science of defining and naming groups of biological organisms on the basis of shared characteristics.

This is a highly complex academic field, which considers enormous amounts of information. Taxonomic consensus changes continously, as more research is completed and more evidence is gathered.

 

Etymology

From Ancient Greek τάξις (táxis) = order, arrangement
From Ancient Greek νόμος (nómos) = law, custom

Taxonomy = the science of arrangement

 

Non-cellular 'life'

These are obligate infectious agents which cannot replicate independently of living organisms.

• Virus
• Prion 

 

The three domains

All living organisms can be categorised into three groups called domains: eukaryota, bacteria and archaea. This system was proposed in 1990.

• Eukaryota 

Eukaryotes are unicellular or multicellular organisms. The cells contain a nucleus enclosed within membranes.

• Prokaryota
• Bacteria
• Archaea 

Prokaryotes are unicellular or multicellular organisms. The cells which lacks a membrane-bound nucleus, mitochondria, or any other membrane-bound organelle.

 

The seven kingdoms

All living organisms can be grouped into kingdoms.
This is a relatively simplistic taxonomic system, which is bothersome to taxonomists, but it is relatively accessible and popular. The 2015 system of 7 kingdoms, proposed by Ruggiero et al. follows below:

• Bacteria
• Archaea
• Protozoa
• Chromista
• Plantae
• Fungi
• Animalia

The kingdoms Chromista and Protozoa include organisms which have been called 'protists' (kingdom: Protoctista). Many sources still (inaccurately) refer to chromists as 'protozoa', 'fungi' or 'animals'.