BIOREADERS: Biological classification

KINGDOM MONERA

The term Monera is came from the Greek word "moneres" which means "single or solitary". This Kingdom consists of unicellular prokaryotic organisms. The Monera was first considered as phylum by Ernst Haeckel in 1866. Later it was changed to kingdom by Edouard Chatton. it is observed in four kingdom, five kingdom, three domain system classification by Herbert F Copeland, R.H. Whitaker and Carl Woese respectively. This kingdom includes Archaebacteria, Eubacteria, Actinomycetes, Mycoplasma, and Spirochetes etc. These lack nuclear envelope and unit membrane bound organelles which are unique features in them.

Archaebacteria:

Also known as Archaea. These are highly diverse with respect to morphology, reproduction, physiology and ecology.They can be gram positive or Gram negative. They may be in rod shaped, spherical shaped, spiral and other. Archaebacteria shows similarity with eubacteria in characteristics like cellular size, absence of nucleus, histones, circular organisation of their genomes, presence of 70S ribosomes, spliceosomal introns, organisation of genes into operons etc. and also metabolic pathways. They re different from eubacteria in information processes such as DNA replication, transcription and translation. However, Archaebacteria are more related to Eukarya than eubacteria in phylogeny.

Archaea are first identified bacterial cells. The cell wall composition of Archaebacteria are different from eubacteria. This contains different cell wall composition. Their cell wall is made up of polysaccharides, glycoproteins or proteins, with no peptidoglycan. Their cell wall made up of polysaccharide Pseudomurein. Pseudomurein is a modified peptidoglycan without D-Amino acids and contains N-acetyltalosaminuronic acid instead of N-acetyl muramic acid which is found in methanogens. All archaea are resistant to lysozyme and beat lactam antibiotics and penicillin.

Major groups of Archaea:-

· Methanogens

· Extreme halophiles

· Thermophiles

Methanogens:

These are methane producing obligate anaerobic. Largest group of archaea found in this group.

production of methane (biogas)

Extreme halophiles:

Halophile

sea with salt survivors

These are survive in very high salt concentrations. Example: Halobacterium salinarium, these can carry out photosynthesis without chlorophyll or bacteriochlorophyll by using bacteriorhodopsin. These are Chemorganoheterotrophs.

Thermophiles:

Philip means loving; these are heat loving agents found near hydrothermal vents and hot springs. The optimum growth temperature is between 70-110°C. They are Gram negative and strict anaerobes.These are extremophiles i.e., they can survive under harsh habitats.

Survival zone	Called as	Examples
High salt conditions	Halophiles	Halobacteriaceae
Hot springs	Thermoacidophiles	Thermos aquaticus
Marshy areas	Methanogens	methanococcus

Eubacteria:

Also called as bacteria. These are the true bacteria (Eu: true) which are unicellular prokaryotic microscopic microorganisms. They vary in shapes. The main shapes we observe in bacteria are spherical, rod, comma, spiral shapes etc. The bacteria were named based on their shapes,

Cocci: These are spherical or round or oval in shape. (Singular: Coccus).

Based on their arrangement cocci are classified as:

· Monococcus: Presence of single cocci.

· Diplococcus: Presence of two cocci.

· Tetrad:Group of four cocci.

· Staphylococcus: Group of cluster of cocci.

· Sarcina: Group of eight cocci.

2. Bacillus: The bacteria which are in rod shape are called bacillus. (Plural: bacilli). These are also classified and named based on their arrangement.

· Streptobacillus: bacillus arranged in a chain.

· Coccobacillus: bacillus is oval and round similar to coccus

3. Vibro: bacteria are in coma shape.

4. Spirillum: bacteria are spiral shape.

The Eubacteria has rigid cell wall made up of Peptidoglycan also called murein or mucopeptide. The genetic material is naked which is not enveloped by nuclear membrane as in all prokaryotes. Cell organelles are absent in all prokaryotes. Ribosomes are present.

When it comes to feed, the bacteria are almost heterotrophy and saprophytic, but few are autotrophy which may be photosynthetic autotrophy or chemosynthetic autotrophy.

Examples of Bacterial species

Differences between Eubacteria and Archaebacteria:

Property	Eubacteria	Archaebacteria
Nucleus	Absent	Absent
Unit membrane bound organelles	Absent	Absent
Cell wall	Peptidoglycan containing muramic acid	Variety of types; no muramic acid
Membrane lipid	Have ester linked, straight-chained fatty acid.	Have ether linked, branched aliphatic chains.

Cyanobacteria:

These are also known as Blue-green algae. These are the most primitive organisms showing oxygenic photosynthesis and these are obligate photolithoautotrophs. Few cyanobacteria are nitrogen fixers which can fix atmospheric nitrogen in specialised cells called heterocysts. These are unicellular colonial or filamentous forms may be branched or unbranched. These are Gram negative bacteria. Their cell wall is made up of peptidoglycan. Photosynthetic pigments present in cyanobacteria are Chl a (but in very few cases Chl b and Chl d also present), carotenoids and phycobilins (phycocyanin and phycoerythrin). The protoplasm of cyanobacterial cell is differentiated into a central colourlesscentroplasmwith chromatin material and peripheral chromoplasm. They often form blooms in polluted water bodies. Their colonies, filaments are surrounded by gelatinous sheath. All cyanobacteria contain thylakoid membranes in which light reactions of photosynthesis and respirations occur. But the genus Gloeobacterwhich is sister group of all cyanobacteria lack thylakoid membranes. Instead they contain ‘Phycobilisomes’ which are light harvesting complexes. Hence, unlike cyanobateria photosynthesis process occurs in plasma membrane instead in thylakoids in these organisms.

The reproduction in cyanobacteria occurs by binary fission, budding, and multiple fission.These produce akinetes under unfavourable condition which protects them during adverse periods. The akinetes are covered with thick walls and appear more in size than vegetative cells. The filamentous cyanobacteria are fragmented into short pieces during fragmentation which are called Harmogonia. Flagella are absent in vegetative or reproductive phases.

Cyanobacteria

Sea with cyanobacterial cells

Trychodesmium erythraeum

Red color of Red Sea

Mycoplasmas:

Mycoplasmas are the smallest and simplest self-reproducing Gram-negative bacteria. These are the only organisms which lack cell wall in Kingdom monera. So, they are placed in a separate class Mollicutes (mollis: soft, cutis: skin). These are pleomorphic and mostly non-motile. These can survive without oxygen i.e.; they are facultative anaerobes. These are parasites, saprophytes, pathogens which cause diseases in animals and plants like Witches broom in plants, Pleuropneumonia in cattle and Mycoplasmal urethritis in humans. These are known as Pleuropneumonia like organisms (PPLO) as they were first isolated in cattle suffering from pleuropneumonia. They cause diseases like Mycoplasmal urethretis, Mycoplasmal genitalium in humans, witches broom, yellow dwarf disease in plants, pleuropneumonia in cattle.

Mycoplasmas

Spirochetes:

The name itself describes that it is in spiral shape or helical shape. These are slender, long, flexible, motile bacteria. These are Gram negative bacteria. The most peculiar feature in spirochetes is their location of flagella which is present in the periplasmic space between the plasma membrane and outer membranes called endoflagella which has axial filaments. They exhibit crawling movements. Their unique pattern of motility is due to axial filaments. These are unusual morphological structures. The central protoplasmic or cell cylinder contains cytoplasm, nucleoid which are bounded by a plasma membrane and Gram-negative type cell wall which is peptidoglycan. The outer membrane contains lipid, protein and carbohydrate. Two to more than hundred Axial filaments or periplasmic flagella are often overlap from both the ends of the cell cylinder. Their habitat is water, sewage, mouth and genital tract in humans etc. They cause diseases like syphilis (causative agent is Treponema pallidum), Lyme disease (causative agent is Borrelia burgdorferi; it has about 7-11 flagella attached near each end of the cell cylinder), leptospirosis (also called Weil’s disease; causative agent is Leptospira interrogans), swine dysentery (Brachyspira hyodysenteriae) etc.

Spirochetes

Actinomycetes:

These are branched filamentous Gram positive bacteria that form radiating colonies in culture. Cell wall made of Mycolic acid. Habitat of these organisms is aquatic or terrestrial. These are saprophytic, parasitic and decomposers. Mycobacterium and Corynebacterium are parasites. Antibiotics are produced from the genus of Steptomyces. Classification of these organisms is mainly based on properties like conidia arrangement, the presence or absence of the sporangium, cell wall type.

Actinomycetes

Streptomyces: It is the largest genus of Actinomycetes. The members in this group are Aerobic, mostly non-pathogenic saprophytes. Their natural mostly of them is soil. The odourness of moist soil is due to release of a volatile substance called ‘geosmin’ from streptomyces. The antibiotics synthesized from streptomyces are amphotericin B, chloramphenicol, erythromycin, neomycin, nystatin, streptomycin, and tetracycline.