Structurally they are similar to Monera in that they have no nuclear membrane and no membranous organelles like mitochondria and chloroplasts. They contain chlorophyll and internal membranes called photosynthetic lamellae or thylakoids. Besides, they also contain pigments phycocyanine (blue) and phycoerythrin (red), which are modified to produce brown, purple, yellow, blue or even red-coloured individuals. They are unicellular or colonial forms which are round, rod-shaped or filamentous. The cell wall is made up of peptidoglycan covered by a characteristic gelatinous envelope. Some cells in the filament are colorless and are called heterocysts which fix free atmospheric nitrogen. The fragmentations take place at these points. They are devoid of flagella but some move by peculiar gliding movement. Food is often stored in the form of oil or glycogen droplets. Some can stand extremes of temperature and pH. The method of reproduction is by binary fission. Since they reproduce extensively, they often become dominant microorganisms in the polluted water of lakes and ponds containing a rich supply of organic matter, forming huge populations often called "blooms". The periodic redness in the oceans is due to blooms of red cyanobacteria. Common examples are Anabaena, Nostoc, Oscillatoria, etc.

Economic importance : Cyanobacteria have the following economic importance :

(i) Heterocyst-bearing forms perform the function of nitrogen fixation. Hence, they are used as biofertilizers in paddy field, to increase yield.

(ii) Non-toxic forms like Spirulina are cultured in large tanks as protein-rich animal feed.

(iii) Nostoc is cultured and used as feed for aquatic animals.

(iv) Some forms like Anabaena and Nostoc make the drinking water poisonous, which can cause death of cattle, birds and even humans. These forms may even interfere with water filtration systems.

 

Fig. 14.12 A few pathogenic bacteria

Role of Monera

1. Role in cycling : Monera are chiefly decomposers concerned in cycling, rotation of metabolites like carbon, hydrogen, nitrogen, and sulphur . in nature. Life on earth would have run out were it not for the decomposition of dead matter by bacteria and release of the elements for resynthesis of cellular compounds. This cyclic journey of chemical elements from biological organisms (bio) through soil or earth crust (geo), is referred to as the biogeochemical cycle.

2. Role in symbiosis : Some forms show symbiotic relationship such as Rhizobium in the roots of leguminous plants or Nostoc and Anabaena in coralloid roots of Cycas, which fix free atmospheric nitrogen into nitrates, and Escherichia coli which inhabit the colon of the human intestine and help in synthesizing Vitamin B.

3. Pathogenic forms : Some Monera are also pathogenic, producing common diseases like typhoid, cholera, diphtheria, tuberculosis and pneumonia in human beings.

List of common bacterial diseases in man

Broad control measures : The broad control measures are as follows:

(i) Use of disinfectants : These are strong chemicals which are distributed where bacteria thrive and multiply. Some common disinfectants used are bleach, phenol, and H₂O₂ peroxide.

(ii) Use of antiseptics : These are mild chemicals which are locally applied to kill bacteria, such as alcohol and iodine.

(iii) Use of antibiotics : These are specific drugs which are used to prevent the growth of bacteria. Some common antibiotics are tetracyclin, streptomycin, penicillin, neomycin and erythromycin.

(iv) Sterilization : This is the common method by which bacteria are killed by excessive heat or ultraviolet irradiation, which disrupts and destroys the protiens and nucleic acids in the bacteria.

Table of Contents

14.0 Introduction
14.1 Kingdom : Monera
14.2 Kingdom : Protista
14.3 Kingdom : Plantae
14.4 Kingdom : Fungi