7. Microbes in human welfare

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·   Lactobacillus or Lactic acid bacteria (LAB):
-    Convert milk to curd.
-    LAB produces acids that coagulate and partially digest the milk proteins.
-    A small amount of curd (which contains LAB) + fresh milk converts to curd. It also increases vitamin B12.
-    In stomach, LAB helps to check pathogens.
·   Bacterial Fermentation (Anaerobic respiration) in dough is used to make foods such as dosa, idli etc. The puffed up appearance of dough is due to the production of CO2 gas.
·   Baker’s Yeast (Saccharomyces cerevisiae): It is used to make bread by fermenting dough.
·   Toddy is made by fermenting sap from palms.
·   Microbes are used to ferment fish, soya bean and bamboo-shoots to make foods.
·   Microbes are used to produce cheeses differing in flavor, taste and texture. E.g.
-    Large holes in ‘Swiss cheese’ are due to production of CO2 by Propionibacterium sharmanii (a bacterium).
-    ‘Roquefort cheese’ is ripened by growing a specific fungus on them that gives them a particular flavor.
Production of beverages, antibiotics etc on an industrial scale, requires growing microbes in very large vessels (fermentors).
Fermented beverages
-    Saccharomyces cerevisiae (Brewer’s yeast) is used in the production of beverages by fermenting malted cereals and fruit juices to produce ethanol.
-    Wine & Beer are produced without distillation.
-    Whisky, Brandy & Rum are produced by distillation of fermented broth.
-    Chemical substances produced by some microbes and can kill or retard the growth of other disease-causing microbes.
-    They are used to treat plague, whooping cough, diphtheria, leprosy etc.
-    Penicillin: First antibiotic discovered by Alexander Fleming. He observed that a mould (Penicillium notatum) growing in unwashed culture plates around which Staphylococci could not grow. He extracted penicillin from it.
-    Earnest chain and Howard Florey established its full potential as an effective antibiotic.
-    Fleming, Chain & Florey were awarded Nobel Prize (1945).
Chemicals, enzymes and other bioactive molecules
1.    Organic acids: E.g.
Aspergillus niger (a fungus)                :    Citric acid
Acetobacter aceti (a bacterium)           :    Acetic acid
Clostridium butylicum (a bacterium)    :    Butyric acid
Lactobacillus (a bacterium)                 :    Lactic acid
2.    Alcohol: Yeast (S. cerevisiae) is used to produce ethanol.
3.    Enzymes:
·   Lipases: Used in detergent formulations. Help to remove oily stains from the laundry.
·   Pectinases & Proteases: To clarify bottled juices.
·   Streptokinase: Produced by Streptococcus. Used as a ‘clot buster’ to remove clots from the blood vessels of patients who have myocardial infarction.
4.    Cyclosporine A: produced by Trichoderma polysporum (fungus). Used as an immunosuppressive agent in organ transplant patients.
5.    Statins: Produced by Monascus purpureus (a yeast). Used as blood-cholesterol lowering agents. It inhibits the enzymes responsible for synthesis of cholesterol.
Sewage (municipal waste-water) contains large amount of organic matter and microbes.
Sewage is treated in Sewage Treatment Plants (STPs) to make it less polluting. It includes 2 stages,
1. Primary treatment
It is the physical removal of particles. It includes
a.    Removal of floating debris by sequential filtration.
b.    Removal of the grit (soil & pebbles) by sedimentation.
All solids that settle form the primary sludge and the supernatant form the primary effluent.
2. Secondary treatment (Biological treatment)
Primary effluent is passed into large aeration tanks and constantly agitated. This allows vigorous growth of useful aerobic microbes into flocs (masses of bacteria associated with fungal filaments to form mesh-like structures). These microbes consume the major part of the organic matter in the effluent. This reduces the BOD (Biochemical Oxygen Demand) of the effluent.
BOD: Amount of O2 consumed by bacteria to oxidize all organic matter in one litre of water. It is a measure of organic matter present in the water. The greater the BOD more is its polluting potential.

The effluent is then passed into a settling tank where the bacterial ‘flocs’ are allowed to sediment. This sediment is called ‘activated sludge’.
A small part of the activated sludge is pumped back into the aeration tank to serve as the inoculum.
The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters. Here, some anaerobic bacteria digest the bacteria and fungi in the sludge by producing gases like CH4, H2S and CO2. These gases form the biogas.
The effluent from secondary treatment plant is released into natural water bodies like rivers and streams.
The Ministry of Environment & Forests has initiated Ganga Action Plan & Yamuna Action Plan to save from water pollution.
-    Biogas: Mixture of gases (mainly CH4) produced by the microbial activity. Biogas is used for cooking & lighting.
-    Methanogens grow anaerobically on cellulosic material and produce CH4. E.g. Methanobacterium.
-    Methanobacterium is found in the anaerobic sludge and rumen of cattle (for cellulose digestion).
-    The dung of cattle (gobar) is rich in these bacteria. Dung can be used for generation of biogas (Gobar gas).
 The Biogas plant
Consists of
·   A concrete tank (10-15 feet deep) to collect bio-wastes and slurry of dung. A floating cover is placed over the slurry, which keeps on rising as the biogas is produced.
·   An outlet which is connected to a pipe to supply biogas.
·   An outlet to remove spent slurry (used as fertilizer).
Indian Agricultural Research Institute (IARI) and Khadi and Village Industries Commission (KVIC): Developed technology of biogas production in India. 
-    Biocontrol: It is the use of biological methods for controlling plant diseases and pests.
-    Chemical pesticides and insecticides are harmful to all organisms and causes pollution. Chemical pesticide kills both useful and harmful life forms.
Microbial biocontrol agents
o Bacillus thuringiensis (Bt): to control butterfly caterpillar.
   These are available in sachets as dried spores which are mixed with water and sprayed on to vulnerable plants such as brassicas and fruit trees, where these are eaten by the insect larvae. In the gut of the larvae, the toxin is released and the larvae get killed.
   The scientists have introduced B. thuringiensis toxin genes into plants. E.g. Bt cotton.
o Trichoderma sp (fungus): are free livings that are seen in the root ecosystems. They are effective biocontrol agents of several plant pathogens.
o Baculoviruses (Especially genus Nucleopolyhedro-virus): Attacks insects and other arthropods.
   These are suitable for species-specific, narrow spectrum insecticidal applications. This is desirable in IPM program to conserve beneficial insects.
·   Biofertilisers are organisms that enrich nutrient quality of the soil. E.g. Bacteria, fungi, cyanobacteria etc.
·   Rhizobium (symbiotic bacteria in root nodules of leguminous plants) fix atmospheric N2.
·   Free-livings in the soil (E.g. Azospirillum and Azotobacter) enrich the nitrogen content of the soil.
·   Mycorrhiza: Symbiotic association of fungi (E.g. the genus of Glomus) with plants. The fungus gets food from the plant. The fungal symbiont
o Absorb phosphorous from soil and passes it to the plant.
o Give resistance to root-borne pathogens and tolerance to salinity and draught.
o Give an overall increase in plant growth and development.
·   Cyanobacteria (Blue green algae): Autotrophic microbes. They can fix atmospheric nitrogen. E.g. Anabaena, Nostoc, Oscillatoria etc. In paddy fields, Cyanobacteria serve as an important biofertilisers. It also adds organic matter to the soil and increases its fertility. 


  1. The BOD incubators are mostly used for the measurements of oxygen in the water. According to bod incubator manufacturers in india it is an amount of oxygen that requires for water bodies to break down organic material that is available in a water sample at a certain temperature.

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