Antibiotics is a Greek word (anti-against-and bios life). Antibiotics are the chemotherapeutic chemical substances which are used in treatment of infectious diseases. Antibiotics are synthesized and secreted by certain bacteria, actinomycetes and fungi. Today, some antibiotics are synthesized in the laboratory. However, their origins are living cells. to determine drug of choice, one must know its mode of action, possible adverse side effects in the human beings.
Use antibiotics as prescribed by the physicians. Take dose at regular intervals and complete the treatment as advised by the doctor.
Massive quantities of antibiotics are being prepared and used, which are followed by the widespread problems of drug resistance in microorganisms. This results in an increasing resistance against disease treatments. Misused antibiotics can interact with the human metabolism and in severe cases can cause death of human beings. Misuse of antibiotic such as penicillin can cause allergic reactions. Similarly streptomycin can affect auditory nerve thus causing deafness. Tetracycline and its related compounds cause permanent discoloration of teeth in young children.
Characteristics of Cyanobacteria
The cynobacteria are the largest and most diverse group of photosynthetic bacteria which was previously known as ‘blue green algae’. Cyanobacteria are true prodaryotes. They vary greatly in shape and appearance. They range in diameter from about 1-10um and may be unicellular, exist as colonies of many shapes, or form filaments consisting of trichomes (chains of cells) surrounded by mucilaginous sheath. They have normal Gram-negative type cell wall. They lack flagella and often use gas vesicles to move in the water, and many filamentous species have gliding motility.
Their photosynthetic system closely resembles that of eukaryotes because they have chlorophyll a and photosystem II. They carry out oxygenic photosynthesis. Cyanobacteria use phycobilins as accessory pigments. Photosynthetic pigments and electron transport chain components are located in thylakoid membranes linked with particles called phycobilisomes. Phycocyanin pigment (blue is their predominant phycobilin and CO2 in them is assimilated through the Calvin cycle.
Reserve food material in cyanobacteria is glycogen. Cyanobacteria reproduce by binary fission, fragmentation. In cyanobacteria hormogonia, akinetes and heterocysts are present.
Fig. 6.8 cyanobacterium anabuena
Economic Importance
They help in reclamation of alkaline soils. Cyanobacteria have heterocysts, which are helpful in the fixation of atmospheric nitrogen. They release O2 in the environment due to their photosynthetic activity. Oscillatoria and few other cyanobacteria can be used as pollution indicator. They have symbiotic relationship with protozoa, fungi, and nitrogen fixing species form associations with angiosperms. They are photosynthetic partner in most of lichen association.
Super Blue green algae are basically expensive pond scum, in which cyanobacterium is a singled celled organism that produces its own food through photosynthesis. It serves as a “complete whole food” which contain 60% protein with all essential amino acids in perfect balance.
Many species of cyanobacteria form water blooms where they often impart unpleasant smell and due to large amount of suspended organic matter water becomes unfit for consumption. Some species produce toxins that kill live stock and other animals that drink the water.
Nostoc
Habitat and occurrence
Nostoc is common as terrestrial and subaerial cyanobacterium. It is widely distributed in alkaline soils and on moist rocks and cliffs. Nostoc forms a jelly like mass in which numerous filaments are embedded.
Structure
Trichomes are unbranched and appear beaded. Individual cells are mostly spherical but some times barrel shaped or cylindrical.
All cells in trichome are mostly similar in structure but at intervals are found slightly large, round, light yellowish thick walled cells called as heterocysts. Trichome mostly breaks near heterocyst and forms hormogonia and thus help in fragmentation.
Reproduction
There is no sexual reproduction but it reproduces asexually by formation of hormogonia. Hormogonia are formed when filament break at different points into smaller pieces. This is due to death and decay of an ordinary cell or the heterocyst may serve as a breaking point. Reproduction can also be due to akinete formation. Akinetes are thick walled, enlarged vegetative cells which accumulate food and become resting cells. On arrival of favouable conditions they form normal vegetative cell.