Amino acid -- The basic building block of proteins and polypeptides. It contains a basic amino group, an acidic carboxyl group, and a side chain to an alpha carbon atom. Amino acids link together by peptide bonds to form proteins, or function as chemical messengers and as intermediates in metabolism.

Bacteriophage, or phage -- A virus that infects and lyses certain bacteria, such as E. Coli. Bacteriophages were discovered by Felix d'Herelle and Frederick Twort in the 1910s. In the 1940s, Max Delbruck encouraged the phage group at Cold Spring Harbor to concentrate their research on seven specific bacteriophages (T1 -- T7), so that they could readily compare results. T2, T4, and T6 are serologically related and have large genomes. T3 and T7 are also related to each other serologically. T1 and T5 are not related to any other bacteriophages.

Cell culture techniques -- Techniques for growing or maintaining cells in vitro. Cultures of dispersed cells derived directly from fresh tissues are called primary cell cultures. Cultures may also be derived from established cell lines, usually stored frozen.

Conjugation -- The one-way transfer of DNA between bacteria in cellular contact.

Culture [bacterial] -- To grow bacteria in a special medium, such as agar, which allows for their rapid reproduction. The term can also refer to the colony of bacteria resulting from this process, or to the laboratory cultivation of living tissue cells.

DNA, or deoxyribonucleic acid -- The primary genetic material of all cellular organisms and the DNA viruses. Located predominately in cell nuclei, it is composed of two chains of nucleotides -- deoxyribose and phosphate backbones with side chains of purine (adenine and guanine) or pyridmidine (cytosine and thymine) bases projecting inward. Hydrogen bonds link adenine to guanine, and cytosine to thymine. The two linked strands are twisted in a double-helix.

Enzyme -- A protein molecule that catalyzes chemical reactions of other substances without itself being destroyed or altered by the reactions. Made up of a complex of amino-acids, enzymes are part of every chemical reaction in living things. They aid in digestion, the growth and building of cells, and all reactions involving transformation of energy. Inside the cell, enzymes create RNA and DNA by facilitating the reaction of ribose with adenosine. They also specify the sites for linking to build RNA along a DNA template. Each enzyme works only on one specific substance (called the substrate). Enzymes are usually designated by the suffix -ase.

Escherichia coli, or E. coli -- A common bacterium that has been studied intensively by geneticists because of its small genome size, normal lack of pathogenicity, and ease of culture in the laboratory.

Exobiology -- A branch of biology concerned with the search for life outside the earth and with the effects of extraterrestrial environments on living organisms. Also called astrobiology.

Genetic engineering -- The group of applied techniques of genetics and biotechnology used to cut and join together genetic material and especially DNA from one or more species of organism and to introduce the result into an organism in order to change one or more of its characteristics. Also a popular term for recombinant DNA technology.

Genetic recombination -- The formation by the processes of crossing-over and independent assortment of new combinations of genes in progeny that did not occur in their parents.

In vitro -- An experimental situation outside a living cell or organism; biological or chemical work done in the test tube, instead of in living systems. "In vitro" is Latin for "in glass."

Mass spectrometry -- An instrumental method for identifying the chemical constitution of a substance by means of the separation of gaseous ions according to their differing mass and charge. Also called mass spectroscopy.

Microbial drug resistance -- The ability of microorganisms, especially bacteria, to resist or become tolerant to chemotherapeutic agents, antimicrobial agents, or antibiotics. The resistance may be acquired through gene mutation or foreign DNA in transmissible plasmids.

Microbial genetics -- A subdiscipline of genetics which deal with the genetic mechanisms and processes of microorganisms.

Molecular biology -- A branch of biology dealing with the formation, structure, and function of macromolecules essential to life, such as DNA, RNA, especially their role in cell replication and the transmission of genetic information.

Mutation -- A relatively permanent change in hereditary material involving either a physical change in chromosome relations or a biochemical change in the codons that make up genes.

Nucleotide -- A unit that polymerizes into nucleic acids (DNA or RNA). Each nucleotide consists of a purine (adenine or guanine) or pyrimidine (cytosine, thymine, or uracil) base, a sugar (ribose in the case of RNA, deoxyribose in the case of DNA), and a phosphate molecule.

Plasmid -- An extrachromosomal, circular, self-replicating DNA found in bacterial cells that carries genes for a variety of functions not essential for cell growth, e.g., antibiotic resistance, production of enzymes or toxins, or ability to metabolize certain nutrients.

Pneumococcus -- A nonmotile bacterium (Streptococcus pneumoniae) that is the most common cause of bacterial pneumonia. It is often associated with meningitis and other infectious diseases.

RNA, or ribonucleic acid -- A single-stranded nucleic acid found in the cell nucleus and cytoplasm, which plays a key role in protein synthesis. (It also constitutes the genetic material of the RNA viruses.) It is similar to DNA but has ribose sugar, rather than deoxyribose sugar, and uracil, rather than thymine, as one of the pyrimidine bases. There are several classes of RNA molecules, including messenger RNA, transfer RNA, and ribosomal RNA, each serving a different purpose in the cell.

Salmonella -- A rod-shaped, gram-negative, aerobic bacterium that grows well on artificial media and forms gas and acid on many carbohydrates but not on lactose or sucrose. Pathogenic for humans and other warm-blooded animals; food poisoning and gastroenteritis are the most common clinical manifestations.

Transduction -- The transfer of genetic material from one organism (as a bacterium) to another by a genetic vector and especially a bacteriophage.

Transformation -- Genetic modification of a bacterium by incorporation of free DNA from another ruptured bacteria cell.

Virulence -- The degree of pathogenicity of a microorganism as indicated by the severity of the disease produced and its ability to invade the tissues of a host. It is measured experimentally by the median lethal dose or median infective dose. By extension, virulence is the competence of any infectious agent to produce pathologic effects.