Single-celled or noncellular spherical or spiral or rod-shaped organisms lacking chlorophyll that reproduce by fission; important as pathogens and for biochemical properties; SYN. bacterium, germ, microbe.
Universally present microscopic unicellular organisms.
Microscopic single-celled organisms lacking a nucleus. Bacteria are widespread, present in soil, air, and water, and as parasites on and in other living things. Some parasitic bacteria cause disease by producing toxins, but others are harmless and may even benefit their hosts. Bacteria usually reproduce by binary fission (dividing into two equal parts), and since this may occur approximately every 20 minutes, a single bacterium is potentially capable of producing 16 million copies of itself in a day. It is thought that 1–10% of the world's bacteria have been identified.
Classification.
Bacteria are now classified biochemically, but their varying shapes provide a rough classification; for example, cocci are round or oval, bacilli are rodlike, spirilla are spiral, and vibrios are shaped like commas. Exceptionally, one bacterium has been found, Gemmata obscuriglobus, that does have a nucleus. Unlike viruses, bacteria do not necessarily need contact with a live cell to become active.
Bacteria can be classified into two broad classes (called Gram positive and negative) according to their reactions to certain stains, or dyes, used in microscopy. The staining technique, called the Gram test after Danish bacteriologist Hans Gram, allows doctors to identify many bacteria quickly.
Bacteria have a large loop of DNA, sometimes called a bacterial chromosome. In addition there are often small, circular pieces of DNA known as plasmids that carry spare genetic information. These plasmids can readily move from one bacterium to another, even though the bacteria may be of different species. In a sense, they are parasites within the bacterial cell, but they survive by coding characteristics that promote the survival of their hosts. For example, some plasmids confer antibiotic resistance on the bacteria they inhabit. The rapid and problematic spread of antibiotic resistance among bacteria is due to plasmids, but they are also useful to humans in genetic engineering. There are ten times more bacterial cells than human cells in the human body.
Functions.
Certain types of bacteria are vital in many food and industrial processes, while others play an essential role in the nitrogen cycle, which maintains soil fertility. For example, bacteria are used to break down waste products, such as sewage; make butter, cheese, and yogurt; cure tobacco; tan leather; and (by virtue of the ability of certain bacteria to attack metal) clean ships’ hulls and derust their tanks, and even extract minerals from mines. In 1995 a US veterinary toxicologist identified several species of bacteria in the stomach of a bowhead whale capable of digesting pollutants (naphthalene and anthracene, two carcinogenic fractions of oil difficult to break down, and PCBs, also carcinogenic). Bacteria cannot normally survive temperatures above 100şC/212şF, such as those produced in pasteurization; but those in deep-sea hot vents in the eastern Pacific are believed to withstand temperatures of 350şC/662şF. Thermus aquaticus, or taq, grows freely in the boiling waters of hot springs, and an en.
Zyme derived from it is used in genetic engineering to speed up the production of millions of copies of any DNA sequence, a reaction requiring very high temperatures.
Interaction.
Certain bacteria can influence the growth of others; for example, lactic acid bacteria will make conditions unfavorable for salmonella bacteria. Other strains produce nisin, which inhibits growth of listeria and botulism organisms. Plans in the food industry are underway to produce super strains of lactic acid bacteria to avoid food poisoning.
Developments.
In 1990 a British team of food scientists announced a new, rapid (five-minute) test for contamination of food by listeria or salmonella bacteria. Fluorescent dyes, added to a liquidized sample of food, reveal the presence of bacteria under laser light.
Bacterial spores 40 million years old were extracted from a fossilized bee and successfully germinated by US scientists 1995. It is hoped that prehistoric bacteria can be tapped as a source of new chemicals for use in the drugs industry. Any bacteria resembling extant harmful pathogens will be destroyed, and all efforts are being to made to ensure no bacteria escape the laboratory.
Unicellular microorganisms that exist either as free-living organisms or as parasites and have a broad range of biochemical, and often pathogenic, properties. Bacteria can be grouped by form into five general categories: cocci (spherical), bacilli (rod-shaped), vibrio (curved rod-shaped), spirilla (spiral), and filamentous (thread-like). + prikaži više

ETYM New Lat., from Greek bakthrion, baktron, a staff: cf. French bactérie.
A microscopic vegetable organism. Bacteria are destitute of chlorophyll, and are the smallest of microscopic organisms.