Archaea:  Single-celled organisms comprising a Domain of life.  These organisms, while similar in appearance to Bacteria, share numerous traits with and are more closely related to Eukaryotes.  Many of these organisms are capable of living in extreme environments (highly acidic, hot, or saline) such as deep sea vents and hot springs.  Recently it has been discovered that these organisms are also surprisingly abundant in non-extreme locations including seawater.

Bacteria: Single-celled organisms comprising a Domain of life. Bacteria are ubiquitous in every habitat on Earth, growing in soil, acidic hot springs, radioactive waste, water, and deep in the Earth's crust, as well as in organic matter and the live bodies of plants and animals.  A 2 liter soda bottle of seawater would likely contain several billion bacterial cells.

Bacteriophage:  A virus that infects bacteria.  Often the shortened form, phage, is used.  This term is also sometimes used to describe viruses infecting archaea.

Capsid:  The protein shell surrounding the viral genome.

Cyanobacteria: A diverse group of bacteria that are capable of oxygen-producing photosynthesis. They occur in all global environments that receive enough sunlight to maintain photosynthetic activity. A single cyanobacterial cell is called a cyanobacterium.

Cyanophage: A group of viruses that infect only cyanobacterial cells.

DNA:  Abbreviation for deoxyribonucleic acid.  DNA is the genetic material of all Bacteria, Archaea, and Eukaryotes, as well as some viruses.  DNA is composed of deoxyribose sugar, phosphates, and four nucleotides: adenine (A), guanine (G), cytosine (C), and thymine (T).

Double Stranded Nucleic Acid:  DNA (dsDNA) or RNA (dsRNA) may exist in a double stranded form, where two molecules interconnect through nucleotide basepairs in a double helix.  dsDNA is found as the genomic material in all cellular organisms, as well as in some viruses.  dsRNA is found only in certain viruses where it acts as the genomic material.

Enveloped Virus:  Viruses that have an outer layer composed of a lipid bilayer membrane (envelope).  These viruses usually “steal” a piece of membrane from the host to form the envelope.

Epidemic:  Disease occurrence in humans at a rate higher than normal.

Eukaryotes:  A domain of life that include organisms with a membrane nucleus containing an organisms genome.  Plants, animals, fungi, algae, and various protozoan groups are eukaryotic.

Genome: The physical entity containing the complete genetic instruction set (that is, all the genes) necessary for making a cell or virus. Genes within the genome are physically comprised of either ribonucleic acid (RNA) or deoxyribonucleic acid (DNA).

Helix:  A spiral shape.  In biological systems: DNA, RNA, and protein may all assume helical form.

Induction:  Lysogenic phage lie dormant within the hosts genome for extended periods of time.  Induction is the process of “waking” these phage genes and initiating viral replication (reproduction).  Induction is usually done by introducing a chemical that introduces damge into the host cell (usually the DNA).

Lysogenic Phage:  Also known as temperate phage.  These bacteriophage incorporate their genetic mmaterial directly into the host genome.  These genes may then lie dormant for extended periods of time before being activated and initiating viral replication (reproduction) and eventual host cell death.

Lytic Phage:  Also known as virulent phage.  These phages enter a cell and immediately use the cell’s biological machinery to replicate (reproduce), rapidly killing the host cell.

Myoviridae:  A family of naked double stranded DNA viruses that infect bacteria.  These lytic phage have a head and tail morphology. The head is composed of the capsid-enclosed genome, while the tail is used to penetrate host cells.  In myoviridae the tail is capable of retracting.

Naked Virus:  Is a virus that does not posses an envelope. In these viruses the capsid forms the outer layer.

Pathogen:  A biological entity that is capable of inducing disease.

Phage (see Bacteriophage)

Podoviridae: A family of naked double stranded DNA viruses that infect bacteria.  These phage have a head and tail morphology. The head is composed of the capsid-enclosed genome, while the tail is used to penetrate host cells.  In podooviridae the tail is short and capable of retracting.

Protein:  Organic compounds composed of amino acids chains.  Proteins are encoded by an organisms genome and are produced from RNA through a process called translation.  Common roles of proteins include catalyzing (assisting) chemical reactions, providing structure, and providing mechanization (cellular motors).

RNA:  Abbreviation for ribonucleic acid.  Acts as the genomic material in some viruses.  RNA is also used as an intermediary step between the genome and protein synthesis in all organisms. RNA is composed of ribose sugars, phosphates, and four nucleotides: adenine (A), guanine (G), cytosine (C), and uracil (U).

Single-stranded nucleic acid:  an individual molecule of DNA (ssDNA) or RNA (ssRNA).  All organisms have ssRNA form that is used as an intermediary in protein synthesis.  Some viruses may also have ss RNA or ssDNA as their genomic material.  ssDNA found in cellular life only briefly during DNA replication.

Siphoviridae: A family of naked double stranded DNA viruses that infect bacteria.  These phage have a head and tail morphology. The head is composed of the capsid-enclosed genome, while the tail is used to penetrate host cells.  In siphoviridae the tail is long and not capable of retracting.

Temperate Phage: (see Lysogenic Phage)

Virulent Phage:  (see Lytic Phage)

Virioplankton: A collection of free virus particles within an aquatic environment.

Virus:  A microscopic biological entity that is not capable of independent reproduction.  In order to replicate (reproduce) viruses must infect a host cell and use the biological machinery of that cell.  All living organisms are susceptible to viral infection, but each virus is capable of infecting only a few (or one) host(s).