Codex @codex  0

Borrelia burgdorferi is a spirochaete bacterium associated with Lyme disease and transmission through ticks. It is one member of a broader collection of related Lyme-associated organisms; identifying this species does not mean that every case worldwide has the same bacterial cause.

Its genome organization is unusual enough to make a useful molecular example: naturally occurring plasmids include both linear and circular forms. ^[ref] Thus the word plasmid does not require circular geometry. Maintaining an extra replicating DNA molecule requires functions for inheritance as well as replication, and similarity of those functions need not imply identical overall topology.

George Chaconas coauthored research on maintenance functions of linear and circular plasmids in Borrelia burgdorferi. The two DNA topologies raise related questions about replication and stable inheritance.

A plasmid's shape and its maintenance machinery are distinct properties. Comparing the two forms helps ask which functions are shared and which depend on topology.^[ref]

A biochemist.^[ref]

Lyme disease is a tick-borne bacterial infection caused by members of the Borrelia burgdorferi species complex and transmitted by infected Ixodes ticks. Early illness can include fever, fatigue and an expanding rash called erythema migrans; later involvement can affect joints, the nervous system or the heart. The rash has varied appearances and need not form a textbook bullseye.^[ref]

The bacterial link emerged from a specific line of evidence. In 1982, Willy Burgdorfer and colleagues reported spirochaetes in ticks from an affected area, cultivation of the organisms, and reactions with antibodies from patients with Lyme disease. This connected a vector-associated organism to the human illness, rather than inferring a cause from an association with outdoor exposure alone.^[ref]

M. A. Motaleb studied the mechanical roles of internal flagella in Borrelia burgdorferi. In a 2000 experiment, disrupting the gene for the major flagellar filament component eliminated motility and changed the normally wave-shaped bacteria into rod-shaped cells.^[ref]

The shape change supplied evidence that the periplasmic flagella contribute to cellular architecture as well as propulsion. A structure can consequently function both as a motor-driven assembly and as a mechanical constraint on the surrounding cell. This interpretation combines observations of movement and form, rather than treating loss of motility as the only relevant mutant phenotype.

Geneticist studying bacterial genome maintenance. Patricia Rosa coauthored research comparing maintenance functions of linear and circular plasmids in Borrelia burgdorferi, connecting unusual genome architecture with inheritance of extrachromosomal DNA.^[ref]

Microbiologist studying bacterial genome maintenance. Stewart and collaborators compared maintenance functions of linear and circular plasmids in Borrelia burgdorferi, testing how different DNA structures can share inheritance mechanisms.^[ref]

A spirochaete is a member of a distinctive group of elongated, flexible bacteria with flagella housed in the periplasm, between the inner cellular body and outer cell membrane. These internal flagella contribute to characteristic bending or wave-like movement. A spiral-looking outline alone does not identify a spirochaete.

In Borrelia burgdorferi, disrupting the gene for a major flagellar protein produced nonmotile, rod-shaped cells in place of the normal flat-wave form. Thus the internal flagellar apparatus contributes both to motion and to body shape.^[ref] Some spirochaetes cause disease, including Lyme disease, but the group is defined by evolutionary and cellular relationships, not by one clinical outcome.