MICROBIAL DIVERSITY
The term 'biological diversity' or biodiversity is defined as the variability among living organisms. The main key of biodiversity on Earth is due to evolution. The structural and functional diversity of any cell represents it evolutionary events which occurred through Darwinian theory of natural selection. Natural selection and survival of the fittest theory is involved on microorganisms. This includes diversity within species, between species and of ecosystems.
Attempts to estimate total number of Bacteria, Archaea and Viruses even more problematic because of difficulties such as detection and recovery from the environment, incomplete knowledge of obligate microbial associates.
Example: Incomplete knowledge of Symbiobacterium thermophilum, and the problem of species concept in these groups.
Further, microbial diversity can be seen on cell size, morphology, metabolism, motility, cell division development 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 spatio-temporal diversity of their hosts or associates.
Revealing Microbial Diversity
The perception of microbial diversity is being radially altered by DNA techniques such as
▪ DNA-DNA Hybridisation
▪ Nucleic Acid Fingerprinting
▪ Methods of assessing the outcome of DNA probing.
▪ 16S rRNA Sequencing
The 16S rRNA has radically changed the classification of microbes into 3 domains,
▪ Bacteria
▪ Archaea
▪ Eukarya
DNA-based analysis:
DNA fingerprinting by restricted length polymorphism i.e., RFLP analysis is accepted techniques for evaluation of relationships between organisms, especially if they are closely related.
The Concept of Microbial Species
Biological diversity or biodiversity is actually evolved as part of evolution of organism, and the smallest unit of microbial diversity is species.
Due to lack of sexuality, fossil records, etc, the adhoc committee on reconciliation of approach to International Committee on Systematic Bacteriology (ICSB) recommended in 1987 that bacterial species would include strains by genotypic, phenotypic and ecological characteristics with approximately 70% or more DNA-DNA relatedness as with 5% or less in thermal stability. Bacterial species is a genomic species based on DNA-DNA relatedness and the modern concept of bacterial species differs from those of other organisms.
Significance of Study of Microbial Diversity
"Microbial diversity encompasses the spectrum of variability among all types of microorganisms in the natural world and as altered by human intervention."
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. Microbial communities are excellent model for understanding biological interactions and evolutionary history. Molecular microbiological method involving DNA-DNA Hybridisation and 16S rRNA Sequencing, etc. 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 form of RNA sequences analysis to prove the metabolic activities and gene regulation of microbes is situ.
Applications
'enriching microbial diversity'
▪ Microbial genomes can be used for recombinant DNA technology and genetic engineering of organisms with environmental and energy related applications.
▪ Culture collections can play a vital role in preserving the genetic diversity of microorganisms.
▪ Microbial informations including molecular, phenotypic, chemical, taxonomic, metabolic and ecological information can be deposited on databases.
▪ Helping in rapid detection and diagnosis and in identification of genes for transfer of desirable properties.
▪ The microbial diversity may be helpful in determining the environmental state of a given habitat of ecosystem.
▪ Could potentially be used as biological weapons.
▪ Microbial diversity of marine microorganisms is equally important, it is helpful to solve the contamination of sea-food by pathogenic microorganisms.
Example: Vibrio vulnificus contaminated oysters.
Microbial Evolution
Use of microbial phylogeneies to determine relatedness, opened up possibility of comparing very diverse microbes with a single yardstick and attempting to deduce their history.
'Failure' of molecular methods of finding a single unambiguous evolutionary progression from a single ancestor to the present panoply of microorganisms.
CLASSIFICATION OF MICROORGANISM
E.Haeckel (1866) separated living organism into three groups - plants, animals and protista. The primitive organisms were included in protista.
(1) Five kingdom System of Classification
▪ Plantae - includes multicellular eukaryotes. Their mode of nutrition is the Photosynthesis.
▪ Fungi - contains eukaryotic and multinucleate organisms. The members have absorptive mode of nutrition.
▪ Animalia - contains multicellular animals devoid of cell wall. Ingestion is the mode of nutrition.
▪ Protista - consists of unicellular or multicellular eukaryotic organisms but true tissues are lacking.
▪ Monera - includes all prokaryotic microorganisms.
for all organisms on the basis of their energy-yielding systems and cell anatomy.
Recently, evolutionary relationships of living organisms have been defined on the basis of ribosomal RNA sequences and other data.
(2) Eight Kingdom System of Classification
Cavalier-Smith (1987, 1993) divided all organisms into two empire
▪ Bacteria
▪ Eukaryota
The empire Bacteria includes two kingdoms - Eubacteria and Archaeobacteria.
The empire Eukaryota contains six kingdoms - Archezoa, Protozoa, Plantae, Chromista, Fungi and Animalia.
(3) Three Domain System of Classification
Woese (1990) established a new superior concept of domains over the kingdom, and proposed three domains.
▪ Bacteria - consists of members which have membrane lipids as diacyl glycerol diesters and eubacterial rRNA.
▪ Archaea - consists of isoprenoid glycerol diester (or diglycerol tetraether) lipids in their membrane and archebacterial rRNA.
▪ Eukarya - includes the organisms which posses glycerol fatty acyldiester as membrane lipids and Eukaryotic rRNA.
MICROBIAL TAXONOMY
Classification, nomenclature and identification comprise taxonomy of microorganisms.
(1) Criteria of Classification & General Methods of Classifying Bacteria
It is important to note that identification may not be based on only a few tests, bit rather on the whole battery of test. Genetic tools are the modern one for identification of bacteria, based on the detection of a specific portion of an organism's genetic material.
The Intuitive Method
The characteristics of organism:
Morphological, physiology, biochemical, genetical, molecular, used to assign an organism.
Numerical Taxonomy
This is based on several characteristics for each strain and each character is given weightage. The % similarity of each strain may determine by the following formula.
% S = NS / (NS+ND)
NS - Number of characteristics for each strains which are similar or dissimilar.
ND - Number of characteristics that are dissimilar or different.
On the basis of % similarity, if it is high to each other, placed into groups larger and so on.
(2) Genetic Relatedness
Based on genetic relatedness (DNA and RNA) between organisms. The % G+C determines the organism whether it is the same or different. Characterization is based on the principles given below:
DNA-DNA Hybridisation or DNA-Homology
After annealing i.e., separation of two strands and converting them into single strand, then mixed with other organism. If organisms are similar pairing will occur in strands of both, and will form heteroduplexes otherwise not.
16S rRNA Sequencing
Ribosomal RNA homology experiments and ribosomal RNA oligonucleotide cataloguing determine the molecular characteristics just to demonstrate degree of relatedness.
Classification and Identification of Bacteria
The use of computers in Bacteriology and in particular taxonomy gave an advantage to resolve the impact of techniques of Numerical Taxonomy. This is based on comparing the strains of bacteria for the large number of characters. A similarity matrix can be drawn up depicting the degree of relationship between all the species examined and it is then presented in form of Dendogram. Adansonian Taxonomy, this system determines the degree of relationship between strains by a statical coefficient that later accounts for their similarity and difference in widest possible range of characters i.e., all phenetic, all of which are of equal importance. The strains, genera for which no term is available, hence are called operational taxonomic units (OTUs).
BERGEY'S SYSTEM OF BACTERIAL CLASSIFICATION
The "Bergey's Manual of Systematic Bacteriology" has volumes that contain the internationally recognised names and descriptions of bacterial species. The details of the informations in the above volumes are summarised below
Vol 1: (Section 1-11) 1984; Gram - negative bacteria.
Vol 2: (Section 12-17) 1986; Gram - positive bacteria, Phototropic and other specialised bacteria including gliding bacteria.
Vol 3: (Section 18-25) 1989; Archaeobacteria
Vol 4: (Section 26-33) 1991; Actinomycetes and other filamentous bacteria.
Comments