Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 122

Bacteria are microscopic, single-celled organisms that thrive in diverse environments. These organisms can live in soil, the ocean, and inside the human digestive system. Bacteria are classified into five groups according to their basic shapes: (i) spherical shapes, also known as cocci, (ii) rod shapes, also known as bacilli, (iii) spiral shapes, also known as spirilla, (iv) comma shapes, also known as vibrios, and (v) corkscrew shapes, also known as spirochaetes which can also exist as single cells, in pairs, chains, or clusters.

Bacteria occur individually or grow as groups ranging from two to millions of individual cells. Individual bacteria cells are small and may be observed only through a microscope. Most bacteria fall into the size range of 0.5 to 3.0 microns (1 micron = 1 m × 10^-6). However, considering all species, a size range of 0.3-50 microns is observed. In general, it is assumed that a filter with a pore size on the order of 0.45 micron will remove all bacteria from water passing through it.

The metabolic activity of bacteria is greatly influenced by their small size. Their surface-to-volume ratio is extremely large, so that the inside of a bacterial cell is accessible to a chemical substance in the surrounding medium. Thus, for the same reason that a finely divided catalyst is more efficient than a more coarsely divided one, bacteria may cause rapid chemical reactions compared to those mediated by larger organisms. Bacteria excrete enzymes that can act outside the cell (exoenzymes) that break down solid food material to soluble components which can penetrate bacterial cell walls, where the digestion process is completed.

Bacteria obtain the energy needed for their metabolic processes and reproduction by mediating redox reactions. Nature provides a large number of such reactions, and bacterial species have evolved that utilize many of these. As a consequence of their participation in such reactions, bacteria are involved in many biochemical processes in water and soil.

Bacteria are essential participants in many important elemental cycles in nature, including those of nitrogen, carbon, and sulfur. They are responsible for the formation of many mineral deposits, including some of iron and manganese. On a smaller scale, some of these deposits form through bacterial action in natural water systems and even in pipes used to transport water.

The presence of coliform bacteria, specifically E. coli (a type of coliform bacteria), in drinking water suggests the water may contain pathogens that can cause a variety of diseases and even death.

See also: Bacterial Mining.