Biology Notes on Microbial Diversity | Microbiology

The below mentioned article provides notes on microbial diversity.

The term ‘microbial diversity’ or biodiversity has become so well known that a public servant is also aware about it. Microbial diversity is defined as the variability among living organisms. The main key of microbial diversity on earth is due to evolution. The structural and functional diversity of any cell represents its evolutionary event which occurred through Darwinian Theory of natural selection.

Natural selection and survival of fittest theory is involved on the microorganisms. This includes diversity within species, between species and of ecosystems. This was first used in the title of a scientific meeting in Washington, D.C. in 1986.

The current list of the world’s biodiversity is quite incomplete (Table 2.1) and that of viruses, microorganisms, and invertebrates is especially deficient. The fungal diversity indicates the total number of species in a particular taxonomic group. The estimates of 1.5 million fungal species is based principally on a ratio of vascular plants of fungi to about 1:6 (Fig. 2.1).

Fig. 2.1 : The number of known species of microorganisms in the world.

Attempts to estimate total numbers of bacteria, archaea, and viruses even more problematical because of difficulties such as detection and recovery from the environment, incomplete knowledge of obligate microbial associations e.g. incomplete knowledge of Symbiobacterium thermophilum, and the problem of species concept in these groups.

Take the case of mycoplasmas, which are prokaryotes having obligate associations with eukaryotic organisms, frequently have tradi­tional nutritional requirements or are mono-culturable and appear to have remarkable diversity. On the other hand, there is one group Spiro plasma, which was discovered in 1972, may be the largest genus on earth.

Spiro plasma species are prin­cipally associated with insects, and the overall rate of new species isolation from such sources of 6% annually indicates species richness. Similarly, marine ecosystems likely support a luxuriant microbial diversity. Further, microbial diversity can be seen on cell size, morphology, metabolism, motility, cell division, developmental biology, adaptation to extreme conditions, etc.

The microbial diversity, therefore, appears in large measure to reflect obligate or facultative associations with higher organisms and to be determined by the spatiotemporal diversity of their hosts or associates.

1. Revealing Microbial Diversity:

The perception of microbial diversity is being radically altered by DNA techniques such as DNA-DNA hy­bridization, nucleic acid fingerprinting and methods of assessing the outcome of DNA probing, and perhaps most important at present, is 16S rRNA sequencing.

The 16S rRNA has radically changed the classification of microbes into 3 domains, the Bacteria, Archaea and Eukarya. While DNA-based analysis (DNA fingerprinting by restriction fragment length polymor­phism i.e. RFLP analysis) is another accepted technique for evaluation of re­lationships between organisms, especially if they are closely related. Holben (1988) detected Brady-rhizobium japonicum selectively at densities as low as 4.3 х 10³ organisms/gram dry soils.

2. The Concept of Microbial Species:

Biological diversity or biodiversity is actually evolved as part of the evolution of organisms, and the smallest unit of microbial diversity is a species. Bacteria, due to lack of sexuality, fossil records etc., are defined as a group of similar strains distinguished sufficiently from other similar groups of strains by genotypic, phenotypic, and ecological characteristics.

The adhoc committee on (he reconciliation of approach to international committee on systematic bacteriology (ICSB) recommended in 1987 that bacterial species would include strains with approximately 70% or more DNA-DNA relatedness and with 5% or less in thermal stability.

Hence, a bacterial species is a genomic species based on DNA-DNA relatedness and the modern concept of bacterial species differs from those of other organisms. To date, more than 69,000 species in 5100 genera of fungi and about 4,760 species of about 700 genera of bacteria have been described in the literature as given in Table 2.1.

3. Significance of Study of Microbial Diversity:

As quoted by American Society of Microbiology under Microbial Diversity Research Priority, “microbial diversity encompasses the spectrum of variability among all types of microorganisms in the natural world and as altered by human intervention”. The role of microorganisms both on land and water, including being the first colonizer, have ameliorating effects of naturally occurring and man-made disturbed environments.

Current evidence suggests there exist perhaps 3 lakh to 10 lakh species of prokaryotes on earth but only 3100 bacteria are described in Bergey’s Manual. More and more information’s are required and will be of value because microorganisms are important sources of knowledge about strategies and limits of life.

There are resources for new genes and organisms of value to biotechnology, there diversity patterns can be used for monitoring and predicting environmental change. Microorganisms play role in conservation and restoration biology of higher organisms. The microbial communities are excellent model for understanding biological interactions and evolutionary history.

Molecular microbiological methods involving DNA-DNA hybridization and 16S rRNA sequencing, etc. now more helpful in establishing microbial diversity. Data bases are becoming more widely available as a source of molecular and macromolecular information on microorganisms. New- technologies are being developed that are based on diverse organisms from diagnostics to biosensors and to biocatalysts.

In the year 1990s’ microbial diversity has burst forward in a new and exciting form due to efforts of environmental microbiologists, who kept the diversity flame alive during the paradigm organism years.

The molecular revolution that has been sweeping through environmental microbiol­ogy has shown how diverse microbes really are. It has also leashed new waves of creativity in the from of RNA sequence analysis to prove the metabolic activities and gene regulation of microbes in situ.

Applications:

The gainful advantages may occur by enriching microbial diversity. Microbial genomes can be used for recombinant DNA technology and genetic engineering of organisms with environmental and energy related applications. Emergence of new human pathogen such as SARS is becoming quite important due to threat to public health can be solved by analyzing the genomes of such pathogen.

Culture collections can play a vital role in preserving the genetic diversity of microorganisms. Microbial information’s including molecular, phenotypic, chemical, taxonomic, metabolic, and ecological information can be deposited on databases. A large number of yet unexplored microorganisms may lead to beneficial information’s.

This can be further strengthened by multidisciplinary involvement of experts. There is a compelling need for discovery and identification of microbial bio-control agents, an assessment of their efficacy etc.,.

The mo­lecular nature of genomes of some important pathogens is necessary to understand the pathogenesis, bio-control, and bioremediation of pollution etc., besides helping in rapid de­tection and diagnosis and in identification of genes for transfer of desirable properties.

Microorganisms are sensitive indicators of envi­ronmental quality. Thus, microbial diversity may be helpful in determining the environmen­tal state of a given habitat of ecosystem. The diverse microorganisms can cause disease and could potentially be used as biological weap­ons. Knowing what is likely to be present can help in rapid diagnosis and treatment.

Biodegradation and bioremediation are potentially important to clean-up and destruction of unwanted materials. Microbial diversity of marine microorganisms is equally important. Sometimes, it is helpful to solve the contamination of sea­food by pathogenic microorganisms e.g. Vibrio vulnificus contaminated oysters. Blue green algae and cyanophages are another dangerous organisms to aquaculture industries.

4. Microbial Evolution:

The microbial evolution has entered a new era with the use of molecular phylogenies to determine relatedness. Certainly this type of phylogenetic analysis remains controversial, but it has opened up possibility of comparing very diverse microbes with a single yardstick and attempting to deduce their history.

Some scientists have opined that the ‘failure’ of molecular methods of find a single unambiguous evolutionary progression from a single ancestor to the present panoply of microorganisms.

The increasing appreciation of the ubiquity and frequency of gene transfer events open the possibility of learning quite essential prokaryotes is by establishing a central core of genes that has not participated in the general orgy of gene transfer. The increasing number of genome sequences may also contribute to a better understanding of the evolutionary history of microbe.