Q. Bacteria - type of microorganisms?

Many of us know bacteria only as "germs," invisible to naked eyes that can invade our bodies and make us sick. Few know that many bacteria not only coexist with us all the time, but help us do an amazing array of useful things like make vitamins, break down garbage, and even maintain our atmosphere. These are unicellular microorganisms that are classed as plants. A bacterial cell is about 1μm in length and somewhat smaller in diameter. Bacteria are classified according to their shape. Cocci are spherical, bacilli are cylindrical and spirilla and vibrios are spiral. Bacterial spores are more heat resistant than yeast or mold spores to most processing conditions. Bacteria, with a few exceptions cannot grow in acid media in which yeasts and molds thrive. They multiply by ‘binary fission'. When a bacterium becomes mature it divides into two, these two become four and so on. Bacteria can be found virtually everywhere. They are in the air, the soil, and water, and in and on plants and animals, including us. A single teaspoon of topsoil contains about a billion bacterial cells (and about 120,000 fungal cells and some 25,000 algal cells).

The human mouth is home to more than 500 species of bacteria. Some bacteria (along with archaea) thrive in the most forbidding, uninviting places on Earth, from nearly boiling hot springs to super-chilled Antarctic lakes buried under sheets of ice. Microbes that dwell in these extreme habitats are aptly called extremophiles. The growth of bacteria is very rapid and depends upon the nature of the food material, moisture, temperature and air. Some bacteria do not grow in air but temperature plays a major role in their growth, the optimum being generally 37°C for bacteria pathogenic to humans.