Chapter 8 Solutions — Microbes in Human Welfare

A suitable sample to carry would be curd (yoghurt) or a small piece of bread left in warm, moist conditions for a day or two.

Curd is an excellent choice because it is made by the action of lactic acid bacteria (LAB) such as Lactobacillus. These bacteria are present in enormous numbers — millions per millilitre — and can be directly mounted on a slide, stained, and observed under a light microscope as rod-shaped or spherical bacteria.

Alternatively, a small scraping from a moist bread surface showing visible mould growth would demonstrate fungal microbes (such as Rhizopus or Penicillium) with clearly visible hyphae and spores.

Curd is the most practical choice because: (i) LAB are always present in large, easily observable numbers; (ii) curd is readily available in any home; (iii) the sample remains stable during transport if kept cool; (iv) no special growth medium or incubation is needed before observation.

Several traditional Indian foods made from wheat, rice, and Bengal gram involve microbial fermentation:

Rice-based foods:

- Idli: Made from a fermented batter of rice and black gram (urad dal). The batter is fermented overnight by bacteria, producing CO₂ that makes idlis soft and spongy.

- Dosa: Made from the same fermented rice and black gram batter as idli. Fermentation by bacteria gives dosa its characteristic slightly sour taste.

Wheat-based foods:

- Bread: Wheat flour dough is fermented using baker's yeast (Saccharomyces cerevisiae), which produces CO₂ causing the dough to rise and giving bread its porous texture.

- Bhattura/Naan: Leavened flatbreads made with wheat flour, in which yeast or LAB are used for fermentation.

Bengal gram-based foods:

- Dhokla: Made from fermented batter of Bengal gram (chickpea) flour and rice flour. Bacterial fermentation produces CO₂ and organic acids giving dhokla its spongy texture and sour taste.

- Khaman: Similar to dhokla, made from fermented Bengal gram batter.

Two fungal species used in the production of antibiotics are:

1. Penicillium notatum (also referred to as Penicillium chrysogenum in industrial production) — produces the antibiotic Penicillin, the first antibiotic to be discovered. Penicillin kills a wide range of disease-causing bacteria.

2. Trichoderma polysporum — produces the bioactive molecule Cyclosporin A. While Cyclosporin A is primarily used as an immunosuppressive agent in organ-transplant patients, it is also an antimicrobial product of fungal origin.

Note: Cephalosporium (Acremonium) species are also used to produce cephalosporin antibiotics, representing another fungal source of antibiotics.