“O Lord, I beg upon my knees that all my various syntheses may not turn out to be inferior to those conducted by bacteria”. —Anon’s quotation boldly points out the importance of bacteria to human beings. The importance of bacteria was further highlighted by J.W. Foster (1964) in his statement “Never underestimate the power of bacteria.”
Bacteria are the simplest of all cellular organisms even though they have undergone evolution for a period of approximately 3.5 to 4 billion years. The layer of viscous material surrounding some bacteria as a capsule or slime layer which has also been referred to as glycocalyx is of great significance to bacteria.
They are very small in size and are represented in different shapes. One trillion or 1012 bacterial cells weigh only 1g. The generation time of Escherichia coli to divide by binary fission is about 20 minutes. In comparison to it a mammalian cell if cultured in a laboratory will take 13 to 24 hours to divide into two cells.
The flagella (singular, flagellum) and the pili (singular, pilus) are the bacterial appendages meant for movement and assist in reproduction respectively. The flagella propel bacteria to move and if compared are faster than most land animals. Bacteria with F pilus are known as donor cells. The cell wall and the cell envelopes are the terms referred to for the protective layers of the bacteria.
The bacterial cells lack membrane bound organelles like mitochondria and chloroplasts found in eukaryotic cells but the cytoplasmic membranes in many of them extend to form mesosomes. The internal cell structures are ribosomes and nucleoid. The chemical substances which are found accumulated are sulphur granules, volutin granules and poly-beta-hydroxybutyrate (PHB). Spores and cysts are metabolically inactive resting forms of bacteria (Fig. 8.1).
There are several techniques of handling bacteria in the laboratory, the most commonly employed methods are microscopy, staining, isolation, cultivation, environmental influences, oligodynamic action, evaluation of disinfectants, physiological characterization and those associated with dairy, soil, water and wastewater, and industry.
After isolating bacteria in pure cultures an important step is to keep them alive by preserving the pure cultures for use in future. If these cultures are to be maintained only for a few days or months they can be stored under refrigerated conditions at temperatures ranging from 4° to 10°C.
However, for long term storage bacteria like other microorganisms can be stored in tanks of liquid nitrogen at -196°C or in deep-freezers at -70° to -120°C. For safe delivery bacteria can be frozen and then dehydrated and sealed under vacuum, the whole process is referred to as lyophilization. The lyophilization or freeze drying assures the viability of bacterial cultures for many years.
The archaeobacteria when seen through the microscope appear similar to bacteria but the two differ in their chemical composition and activities and the environment in which they can survive. Many archaeobacteria survive in adverse conditions under high levels of ‘salt or acid or high temperature.
Some of the archaeobacteria are endowed with unique chemical activities such as production of methane gas from carbon dioxide and hydrogen. The methane producing archaeobacteria live in habitats without oxygen like deep swamp mud or the intestines of cattle and sheep that chew cud. The eubacteria on the other hand are necessary in recycling wastes and the production of antibiotics such as streptomycin. Streptococcal sore throat, tetanus, plague, cholera and tuberculosis are some of the diseases caused by the eubacteria.