Bacterial Viruses

Production of new viruses and viral DNA with the introduction of a genome’s virus into a host bacteria are bacterial viruses. Such viruses are capable of infecting any cell type, unicellular, plant or animal cell.

The infecting bacteria are known as bacteriophage. When they are present exterior to the bacterial cells these exist as inert substances. It has complex protein coats with a structure, well-defined, and may also have tail structures. The capsid or protein coat wraps the DNA or RNA molecule making up the bacteriophage genome. These genomes are either linear or circular, and single or double stranded. Various bacteriophages in their genome encode as little as 4 proteins or as high as a hundred proteins.

A similar factor in phages in comparison to animal and plant viruses is that they are non-living as they are not capable of replicating on themselves or carrying out any metabolic processes. Though each type of phage displays a defined host range, all phages need bacterial cells to reproduce. A few phages are species-specific to one or two of the related species, some others can infect and replicate in a range of bacterial cells.

The host range is defined by the host cell functions necessitated for reproduction of bacteriophages such as injecting bacteriophage DNA in the cytoplasm of the bacterial cell, attaching to specific molecules on the cell surface of the bacteria, refraining from host cell defenses, synthesis and assemblage of capsid, suitable regulation and expression of the bacteriophage genes, packaging nucleic acids into the capsid, replicating nucleic acids of the phage, moving out of the bacterial cells.

Bacteriophages – Properties

There is no dearth in the variety of phages existing today. This clan is restricted to infecting either 1 type or a range of bacterial types. They can be categorized in many families of viruses such as Rudiviridae, Microviridae, and Inoviridae and more. Phages are less complicated, simple entities as viruses consisting of genetic content wrapped by protein capsid. Structurally, three forms of phages are known – a 20-headed icosahedral head and a tail, an icosahedral head where the tail is absent and a filamentous form.

Bacteriophage – Life Cycle

When there is any infection, a phage secures itself to a bacteria and introduces its genetic content into the cell. Post this step, a phage follows either of these two life cycles – virulent (lytic) or the temperate (lysogenic).

The generated phage components, the lytic phage overtakes the machinery of the cell after which they kill the cell or the lyse liberating new particles of phage. Whereas, the lysogenic phages merge their nucleic acid content into the host cells’ chromosomes to replicate as a unit unaccompanied by the need to kill the cell. The lysogenic phages in some situations may be induced to follow a lytic cycle.

Chronic infection and pseudolysogeny are some more life cycles. Bacteriophages in pseudolysogeny are introduced in the cell however, they neither co-opt the replication of the cell scheme nor does it integrate with stability into the host genome. Psuedolysogeny takes place whenever the host cell experiences adverse growth conditions and seemingly plays a significant role in the survival of the phage by allowing the preservation of the phage genome until the growth conditions of the host have turned beneficial. New phage particles in chronic infection are continuously synthesized over long durations without killing the cell.

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