Concept of microbial species and strains
Biodiversity is defined as the variability among the living organisms. This includes diversity within species, between species, and species of ecosystems. The current list of world's biodiversity is incomplete especially about viruses, microorganisms and invertebrates. to estimate total number of viruses and bacteria is more difficult due to difficulties in detection, recovery from the environment, incomplete knowledge of obligate microbial associations.
Biodiversity evolved with the evolution of organisms and microorganisms. Bacteria due to lack of sexuality, fossile records, etc are defined as a group of similar strains distinguished from other similar strains by genotypic, phenotypic and ecological characteristics.
International Committee of Systematic Bacteriology(ICSB) in 1987 recommended that species include strains with 70% DNA-DNA relatedness and with 5% in thermal stability. Hence a bacterial species is a genomic species based on DNA-DNA relatedness. The modern concept of bacterial species in differ from those of other organisms.
At present more than 69,000 species of fungi are known in 5100 genera, about four thousand seven hundred sixty species of bacteria are known in 700 genera as per the described literature.