KEY POINTS
v Microbiologists place bacteria in tow major categories eubacteria (Greek for “true bacteria’) and a much smaller division archaeobacteria (Greek for “ancient bacteria”).
v A Dutch scientist “Antone Van Leeuewenhoek” was the first to report the microbes such as bacteria and protozoa. He used a simple microscope to describe and protozoa with.
v Accurate drawings and descriptions and called these small creatures as “Animalcules”.
v The main achievements of Louis Pasteur’s are the development of vaccines for diseases “Anthrax”, “fowl cholera” and “Rabies”.
v Louis Pastures proved that micro-organisms could cause diseases.
v Robert Koch formulated the “germ theory of diseases”. He isolated typical rod shaped bacteria from the blood of sheep that has died of Anthrax. He formulated four postulates. Which are the main pillars of the germ theory of diseases?
v All bacteria cell invariably have a cell membrane cytoplasm, ribosomes and chromatic bodies.
v The majority have cell wall, which gives shape to the bacterial cell. Specific structures like capsule, slime, flagella, pili, fimbriae and granules are not found in all bacteria.
v The smallest bacteria are about 100 to 200nm in diameter, approximately the size of largest viruses i.e. poxviruses e.g. some members of genus Mycoplasma.
v Escherichia Coli, a bacillus of about average size, is 1.1 – 1.5µm wide by 2.0 – 6.0µm long.
v Some spirochetes occasionally reach 500µm in length staphylococci and streptococci are 0.75 – 1.25µ in diameter.
v If division is in one plane it will produce either a diplococcus or streptococcus arrangement. When cocci occur in pairs, then arrangement is diplococcus. When cocci form long chains of cells then arrangement is called a streptococci.
v When the division is in three palnes it will produce a Sarcina arrangement. Sarcina is a cube of 8 cocci.
v When the division of cell is in tow planes, it will produce a tetrad arrangement. A tetrad is a square of 4 cocci.
v When division occurs in random planes it will produce a staphylococcus arrangement in which cocci are arranged in irregular often grape-like clusters.
v Vibrio is a curved or comma-shaped rod. Spirillum is a thick, rigid spiral whereas Spirochete is a thin, flexible fibre.
v Flagella are extremely thin hair like structures. They come out through cell wall and originate from basal bodies, structures just beneath the cell membrane in the cytoplasm. It is made up of protein “Flagellin”.
v “Atrichous” means bacteria are without any flagella. When single polar flagellum is present then condition is known as “Monotrichous”. It tuft of flagella is present only at one pole of bacteria than are “Lophotrichous” to flagella. “Amphitrichous” is a condition when tuft of flagella at each of tow poles is present. In “Peritrichous” form flagella surround the whole cell.
v Cocci very rarely have flagella.
v With the help of flagella, flagellated bacteria can also detect and move in response to chemical signals which is a type of behaviour called as “Chemotoxis”.
v True “Pili” are only present in gram-negative bacteria.
v Pili are primarily involved in a mating process between cells called “Conjugation process”. Some pili function as a mean of attachment of bacteria to various surfaces.
v Slime provides greater pathogenity to bacteria and protects them from phagocytosis.
v Cell wall is only absent in Mycoplasmas.
v Cell wall of most bacteria have a unique macromolecule called as Peptidoglycan. Its amount varies in different types of bacteria.
v Peptidoglycan is composed of frames of long glycean chains cross linked with peotide fagements. The intact cell wall also contains chemical constituents such as sugar molecules, teichoic and lipoprotein and lipopolysaceharde which are linked to peotidoglycan.
v Bacterial membrane differs from eukaryotic membrane is lacking sterols such as cholesterol.
CHARACTERISTICS | GRAM-LOSITIVE | GRAM-NEGATIVE |
Number of major layers | 1 | 2 |
Chemical make up | Peptidoglycan (50% of dry weight in some bacterial cells), techoic acid and lipotechoic acid, lipids (1-4%) | Lipopolysaccharides, lipoproteins, peptidoglycan (10% dry weight of some bacterial cells), lipids (11-12%) |
Overall thickness | 20-80nm | 8-11nm |
Outer membrane | No | Yes |
Periplasmic space | Present in some | Present in all |
Permeability | More permeable | Less permeable |
v The plasma membrane of bacteria also contains enzymes for respiratory metabolism.
v Disease and insect resistance genes are found on plasmid.
v Pseudomonas is an aerobic, spirochete is an anaerobic, E coli is a facultative anaerobic and campylobacter is a microaerophilic bacterium.
v Chemical substances used on living tissues hat inhibit the growth of micro organism are called “Antiseptics”.
MODES OF NUTRITION IN BACTERIA
v The important chemical agents used fro disinfection are oxidizing and reducing agents.
v Chemotherapeutic and antibiotics work with natural defense and stop the growth of bacteria and other microbes.
v Streptomycin can affect auditory nerve thus causing deafness.
v The “Cyanobactria” are the largest and most diverse group of photosynthetic bacteria which were previously known as “Blue green algae”.
v Cynobacteria have normal gram -ve cell wall.
v Their photosynthetic system closely resembles that of eukaryotes because they have chlorophyII a and photosystem II.
v Cyanobacteria contain phycobilins as accessory pigments.
v Photosynthetic pigments and electron transport chain components are located in thylakoids membranes linked with particles called phycobilisimes.
v Phycocyanine (blue) is their predominant phycobilin and CO2 in them is assimilated through calvin cycle.
v Reserve food material in cyanobacteria is glycogen.
v Oscillatoria and few other cyanobacteria can be used as pollution indicators.
v Super blue green algae are basically expensive pond scum.
v Nostoc is widely distributed in alkaline soils and on moist rocks and cliffs.
v Akinetes are thick walled enlarged vegetative cells which accumulate food and become “Resting Cells.
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