Microbes

Microbes play a major role in treating millions of gallons of waste water every day across the globe. This methodology has been practised for more than a century now, in almost all parts of the world. Till date, no man-made technology has been able to rival the microbial treatment of sewage. --- ### Sewage Treatment Municipal wastewater (sewage) contains large amounts of organic matter and microbes, many of which are pathogenic. It cannot be discharged directly into natural water bodies. Treatment is carried out by heterotrophic microbes naturally present in the sewage. Treatment is done in **two stages:** **Primary Treatment (Physical):** - Physical removal of particles — large and small — through filtration and sedimentation - Floating debris removed by sequential filtration - Grit (soil and small pebbles) removed by sedimentation - All solids that settle form the **primary sludge**; supernatant forms the effluent which goes for secondary treatment **Secondary Treatment (Biological):** - Primary effluent passed into large **aeration tanks** where it is constantly agitated mechanically and air is pumped in - Vigorous growth of useful aerobic microbes into **flocs** — masses of bacteria associated with fungal filaments to form mesh-like structures - Growing microbes consume the major part of organic matter in the effluent - This significantly reduces the **BOD (Biochemical Oxygen Demand)** of the effluent - **BOD** = amount of oxygen that would be consumed if all organic matter in one litre of water were oxidised by bacteria. The sewage water is treated till the BOD is reduced. Greater BOD = greater polluting potential - Once BOD is reduced significantly, effluent is passed into a **settling tank** where bacterial flocs are allowed to sediment → this sediment is called **activated sludge** - A small part of activated sludge is pumped back into aeration tank as inoculum - Remaining major part of sludge is pumped into large tanks called **anaerobic sludge digesters** - In anaerobic sludge digesters, other bacteria (anaerobic) digest the bacteria and fungi in the sludge. During digestion, bacteria produce a mixture of gases: **methane, hydrogen sulphide and carbon dioxide** → these form **biogas** → can be used as energy source (inflammable) - Effluent from secondary treatment plant is generally released into natural water bodies **Ganga Action Plan and Yamuna Action Plan:** Initiated by the Ministry of Environment and Forests to save these major rivers from pollution; proposed to build a large number of sewage treatment plants so that only treated sewage may be discharged into rivers. --- ### Biogas Production **Biogas** is a mixture of gases (containing predominantly **methane**) produced by the microbial activity which may be used as fuel. Bacteria that grow anaerobically on cellulosic material produce large amounts of methane along with CO₂ and H₂S. These bacteria are collectively called **methanogens**. One such common bacterium: **Methanobacterium**. - Methanobacterium are commonly found in the anaerobic sludge during sewage treatment - These bacteria are also present in the **rumen** (a part of stomach) of cattle — they help in the breakdown of cellulose and play an important role in nutrition of cattle - 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** **Biogas plant construction:** - 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 - As bacteria digest the dung and other bio-wastes, gases are produced and collected in the dome-shaped cover - The gas is then supplied through pipes for use as fuel **Significance:** The Ministry of Environment and Forests reports sewage is being produced in much larger quantities due to increasing urbanisation. The number of sewage treatment plants has not increased enough — untreated sewage is often discharged directly into rivers leading to their pollution and increase in water-borne diseases. --- ### Integrated Waste Water Treatment — Arcata, California An example of integrated wastewater treatment using a mix of artificial and natural processes: - Conventional sedimentation, filtering and chlorine treatments (Stage a) - Followed by a series of six connected marshes over 60 hectares with appropriate plants, algae, fungi and bacteria seeded in (Stage b) - As water flows through marshes, it gets purified naturally - Marshes also constitute a sanctuary with high level of biodiversity ---

Microbes (bacteria, fungi, protozoa, viruses, and some algae) are ubiquitous — they are present everywhere in soil, water, air, inside and outside our bodies. Many microorganisms are beneficial and have been used by humans since antiquity for food production, and in modern times for producing medicines, industrial products, and agricultural inputs. --- ### Microbes in Food - **Curd:** Lactobacillus and other lactic acid bacteria (LAB) convert pasteurised milk to curd (yoghurt). LAB produce acids that coagulate and partially digest the milk proteins. LAB also increase the nutritional quality (by increase of Vitamin B₁₂) and check disease-causing microbes - **Bread:** Yeast **Saccharomyces cerevisiae** — dough is leavened by CO₂ produced by yeast - **Alcoholic beverages:** Same yeast Saccharomyces cerevisiae is used for commercial production of ethanol; also used for wine, beer, whisky, brandy or rum - **Toddy** (a traditional drink of some parts of southern India) — made by fermenting sap from palms - **Cheese:** Different varieties made using microbes. Large holes in **Swiss cheese** are due to production of large amounts of CO₂ by bacterium **Propionibacterium shermanii**. Roquefort cheese is ripened using fungi - **Fermented foods:** Idli, dosa made from fermenting rice and black gram dough; **Butyric acid** formed by Clostridium; **Lactic acid** by Lactobacillus - **Industrial enzymes from microbes:** Lipases (used in detergent formulations, removes oily stains); Pectinases and proteases (clarify bottled fruit juices — make them clearer); Streptokinase from Streptococcus (modified by genetic engineering) used as 'clot buster' for removing clots from blood vessels of patients with myocardial infarction --- ### Antibiotics **Antibiotic** means "against life" — chemical substances produced by one microbe that can kill or retard the growth of other (disease-causing) microbes. **Penicillin — the first antibiotic:** - Discovered by **Alexander Fleming** (chance discovery) while working on Staphylococci bacteria. He observed a mould growing in one of his unwashed culture plates around which Staphylococci could not grow. He found it was due to a chemical produced by the mould and named it **Penicillin** after the mould **Penicillium notatum** - Its full potential as an effective antibiotic was established much later by **Ernest Chain and Howard Florey** - This antibiotic was extensively used to treat American soldiers wounded in World War II - **Fleming, Chain and Florey were awarded the Nobel Prize in 1945** for this discovery After Penicillin, other antibiotics were also purified from other microbes. Antibiotics have greatly improved our capacity to treat deadly diseases. --- ### Other Bioactive Molecules - **Cyclosporin A:** Bioactive molecule used as an **immunosuppressive agent** in organ-transplant patients. Produced by the fungus **Trichoderma polysporum** - **Statins:** Produced by the yeast **Monascus purpureus**; commercialised as blood cholesterol-lowering agents. Act by competitively inhibiting the enzyme responsible for synthesis of cholesterol (HMG-CoA reductase) - **Streptokinase** (clot buster): produced by Streptococcus and modified by genetic engineering — removes blood clots from vessels of myocardial infarction patients --- ### Microbes in Agriculture — Biofertilisers **Biofertilisers** are organisms that enrich the nutrient quality of soil. Main sources: 1. **Bacteria:** - **Rhizobium:** Lives in symbiotic association with roots of leguminous plants; fixes atmospheric nitrogen in root nodules - **Azospirillum** and **Azotobacter:** Free-living nitrogen-fixing bacteria; fix atmospheric nitrogen and enrich nitrogen content of soil - **Cyanobacteria (blue-green algae):** Such as **Anabaena**, **Nostoc**, **Oscillatoria** — free-living or symbiotic in aquatic environments; fix atmospheric nitrogen. An important biofertiliser in paddy fields 2. **Fungi — Mycorrhiza:** - **Glomus** species form symbiotic associations with plants (mycorrhiza) - The fungus absorbs phosphorus from soil and passes it to the plant - Plants also show other benefits: resistance to root-borne pathogens, tolerance to salinity and drought, and overall increase in plant growth and development ---