Which microbe does which job

The whole chapter in one table

The marks in this chapter go to those who know which microbe does which job. Read the table, then cover a column and test yourself.

• Lactobacillus, bacterium: curd, and lactic acid.
• Saccharomyces cerevisiae, yeast: bread dough, and ethanol of wine, beer, whisky, brandy, rum.
• Propionibacterium sharmanii, bacterium: large holes of Swiss cheese.
• A specific fungus: flavour of Roquefort cheese.
• Aspergillus niger, fungus: citric acid.
• Acetobacter aceti, bacterium: acetic acid.
• Clostridium butylicum, bacterium: butyric acid.
• Penicillium notatum, fungus: penicillin.
• Streptococcus, bacterium: streptokinase, the clot buster.
• Trichoderma polysporum, fungus: cyclosporin A.
• Monascus purpureus, fungus (a yeast in NCERT): statins.
• Methanobacterium, bacterium: methane of biogas.
• Bacillus thuringiensis, bacterium: biocontrol of caterpillars.
• Trichoderma, fungus: biocontrol of plant pathogens.
• Baculovirus, virus: biocontrol of insects.
• Rhizobium, bacterium: nitrogen fixing, in root nodules of legumes.
• Azospirillum, Azotobacter, bacteria: free-living nitrogen fixing.
• Glomus, fungus: mycorrhiza, phosphorus.
• Anabaena, Nostoc, Oscillatoria, cyanobacteria: nitrogen fixing, paddy fields.

Other things to remember

• Sewage plant: primary treatment is physical. Secondary treatment uses aerobic microbes that grow as flocs. The sediment is the activated sludge. Anaerobic digesters make biogas.
• BOD: the oxygen needed to oxidise the organic matter of 1 L of water.
• Biogas: mostly methane. Methanogens are anaerobic. IARI and KVIC.

The usual traps

1. One genus, two jobs. Trichoderma is a biocontrol fungus, and Trichoderma polysporum is the NCERT source of cyclosporin A. Bacillus thuringiensis is the spray, and Bt cotton is the plant with its gene.
2. Free living or symbiotic. Rhizobium is symbiotic. Azotobacter and Azospirillum are free-living.
3. Nitrogen or phosphorus. Nitrogen: Rhizobium, Azotobacter, Azospirillum, cyanobacteria. Phosphorus: mycorrhiza.
4. Aerobic or anaerobic. The aeration tank has aerobic microbes. The digester and the biogas plant have anaerobic ones.
5. Distilled or not. Wine and beer are not distilled. Whisky, brandy and rum are.
6. Bacterium or fungus. Aspergillus, Penicillium, Trichoderma, Monascus and Glomus are fungi.

You should be able to name the microbe before you read it. Go through the six jobs twice, and then try the table again with a column covered.

Try it in Python

The program keeps the jobs and the microbes in a dictionary, and looks one of them up.

Practise with new numbers

Common mistakes

• Giving a product to the wrong microbe. Say the pair as a whole: microbe, group, product.
• Treating a yeast as a bacterium. Saccharomyces is a yeast, which is a fungus.
• Saying that cyanobacteria are fungi. They are bacteria that photosynthesise.
• Forgetting that biofertilisers and biocontrol agents are different jobs. One feeds the soil and the other kills pests.
• Mixing up the organism of the sewage plant and the organism of the biogas plant. The first is aerobic and the second is anaerobic.

Remember these

• Fungi: Aspergillus niger, Penicillium, Trichoderma, Monascus purpureus, Glomus, a Roquefort fungus, and the yeast Saccharomyces cerevisiae.
• Bacteria: Lactobacillus, Propionibacterium, Acetobacter, Clostridium, Streptococcus, Methanobacterium, Bacillus thuringiensis, Rhizobium, Azospirillum, Azotobacter.
• Virus: baculoviruses. Cyanobacteria: Anabaena, Nostoc, Oscillatoria.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. Which microbe makes citric acid, which makes acetic acid, and which makes butyric acid?

2. Which microbe fixes nitrogen in the nodules of legumes, and which two fix it as free-living bacteria?

3. Which fungus helps a plant to take up phosphorus?

4. Name one microbe that is used for the control of insects and one that is used for the control of plant pathogens.

5. In which part of a sewage plant, and in which part of a biogas plant, are the microbes aerobic, and in which anaerobic?

References

• NCERT (2023). Biology, Textbook for Class XII, chapter 8, Microbes in Human Welfare.
• Madigan M. T. et al. (2019). Brock Biology of Microorganisms, 15th edition, Pearson, the chapters on industrial microbiology and on nitrogen fixation.