Microbes in Human Welfare
Microbes in Production of Biogas
Biogas is a mixture of gases (containing predominantly methane) produced by the microbial activity and which may be used as fuel
You have learnt that microbes produce different types of gaseous end-products during growth and metabolism
The type of the gas produced depends upon the microbes and the organic substrates they utilise
In the examples cited in relation to fermentation of dough, cheese making and production of beverages, the main gas produced was CO2.
However, certain bacteria, which grow anaerobically on cellulosic material, produce large amount of methane along with CO2 and H2
These bacteria are collectively called methanogens, and one such common bacterium is Methanobacterium
These bacteria are commonly found in the anaerobic sludge during sewage treatment
These bacteria are also present in the rumen (a part of stomach) of cattle
A lot of cellulosic material present in the food of cattle is also present in the rumen
In rumen, these bacteria help in the breakdown of cellulose and play an important role in the nutrition of cattle
Do you think we, human beings, are able to digest the celluose present in our foods? Thus, the excreta (dung) of cattle, commonly called gobar, is rich in these bacteria
Dung can be used for generation of biogas, commonly called gobar gas
The biogas plant consists of a concrete tank (10-15 feet deep) in which bio-wastes are collected and a slurry of dung is fed
A floating cover is placed over the slurry, which keeps on rising as the gas is produced in the tank due to the microbial activity
The biogas plant has an outlet, which is connected to a pipe to supply biogas to nearby houses
The spent slurry is removed through another outlet and may be used as fertiliser
Cattle dung is available in large quantities in rural areas where cattle are used for a variety of purposes
So biogas plants are more often built in rural areas
The biogas thus produced is used for cooking and lighting
The picture of a biogas plant is shown in Figure 8.8
If your school is situated in a village or near a village, it would be very interesting to enquire if there are any biogas plants nearby
Visit the biogas plant and learn more about it from the people who are actually managing it
Microbes as Biocontrol Agents
Biocontrol refers to the use of biological methods for controlling plant diseases and pests
In modern society, these problems have been tackled increasingly by the use of chemicals - by use of insecticides and pesticides
These chemicals are toxic and extremely harmful, to human beings and animals alike, and have been polluting our environment (soil, ground water), fruits, vegetables and crop plants
Our soil is also polluted through our use of weedicides to remove weeds
Biological control of pests and diseases: In agriculture, there is a method of controlling pests that relies on natural predation rather than introduced chemicals
A key belief of the organic farmer is that biodiversity furthers health
The more variety a landscape has, the more sustainable it is
The organic farmer, therefore, works to create a system where the insects that are sometimes called pests are not eradicated, but instead are kept at manageable levels by a complex system of checks and balances within a living and vibrant ecosystem
The organic farmer holds the view that the eradication of the creatures that are often described as pests is not only possible, but also undesirable, for without them the beneficial predatory and parasitic insects which depend upon them as food or hosts would not be able to survive
Thus, the use of biocontrol measures will greatly reduce our dependence on toxic chemicals and pesticides
An important part of the biological farming approach is to become familiar with the various life forms that inhabit the field, predators as well as pests, and also their life cycles, patterns of feeding and the habitats that they prefer
This will help develop appropriate means of biocontrol
The very familiar beetle with red and black markings - the Ladybird, and Dragonflies are useful to get rid of aphids and mosquitoes, respectively
An example of microbial biocontrol agents that can be introduced in order to control butterfly caterpillars is the bacteria Bacillus thuringiensis (often written as Bt )
These are available in sachets as dried spores which are mixed with water and sprayed onto 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 bacterial disease will kill the caterpillars, but leave other insects unharmed
Because of the development of methods of genetic engineering in the last decade or so, the scientists have introduced B
thuringiensis toxin genes into plants
Such plants are resistant to attack by insect pests
Bt-cotton is one such example, which is being cultivated in some states of our country
You will learn more about this in chapter 12
A biological control being developed for use in the treatment of plant disease is the fungus Trichoderma
Trichoderma species are free-living fungi that are very common in the root ecosystems
They are effective biocontrol agents of several plant pathogens
Baculoviruses are pathogens that attack insects and other arthropods
The majority of baculoviruses used as biological control agents are in the genus Nucleopolyhedrovirus
These viruses are excellent candidates for species-specific, narrow spectrum insecticidal applications
They have been shown to have no negative impacts on plants, mammals, birds, fish or even on non-target insects
This is especially desirable when beneficial insects are being conserved to aid in an overall integrated pest management (IPM) programme, or when an ecologically sensitive area is being treated
Microbes as Biofertilisers
With our present day life styles environmental pollution is a major cause of concern
The use of the chemical fertilisers to meet the ever-increasing demand of agricultural produce has contributed significantly to this pollution
Of course, we have now realised that there are problems associated with the overuse of chemical fertilisers and there is a large pressure to switch to organic farming - the use of biofertilisers
Biofertilisers are organisms that enrich the nutrient quality of the soil
The main sources of biofertilisers are bacteria, fungi and cyanobacteria
You have studied about the nodules on the roots of leguminous plants formed by the symbiotic association of Rhizobium
These bacteria fix atmospheric nitrogen into organic forms, which is used by the plant as nutrient
Other bacteria can fix atmospheric nitrogen while free-living in the soil (examples Azospirillum and Azotobacter), thus enriching the nitrogen content of the soil
Fungi are also known to form symbiotic associations with plants (mycorrhiza)
Many members of the genus Glomus form mycorrhiza
The fungal symbiont in these associations absorbs phosphorus from soil and passes it to the plant
Plants having such associations show other benefits also, such as resistance to root-borne pathogens, tolerance to salinity and drought, and an overall increase in plant growth and development
Can you tell what advantage the fungus derives from this association? Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments many of which can fix atmospheric nitrogen, e.g
Anabaena, Nostoc, Oscillatoria, etc
In paddy fields, cyanobacteria serve as an important biofertiliser
Blue green algae also add organic matter to the soil and increase its fertility