Spirochetes use an axial filament to be motile. This is similar to a cellular flagella but this structure wraps through the whole cell. It is located between the periplasmic space between the inner and outer membranes of the cell.

Axial Filament 

Which of the following best describes spirochete cells?

Which of the following statements is true about spirochete cells?

Which of the following diseases is commonly associated with spirochete bacteria?

What is a distinguishing feature of spirochete bacteria?

The term spirochete (plural: spirochetes) refers to prokaryotic cells that have a long, loose, and flexible helical spiral shape. They visually appear similar to spirilla but are noticeably more floppy. They are members of the Spirochaetota phylum.

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Individual cells of a specific prokaryotic organism typically exhibit a characteristic shape, known as cell morphology. While thousands of prokaryotic organisms exist, only a handful of morphologies are commonly seen microscopically. These standard shapes include spherical (coccus), rod-shaped (bacillus), curved comma-shaped (vibrio), short oval-like rods (coccobacillus), long rigid corkscrews (spirillum), and loose, flexible helical spirals (spirochete).

Cell Morphologies

The gram negative bacteria that are not present in the Proteobacteria phylum consist of some of these classes and genera of bacteria:
-  *Chlamidia*
- Spirochetes
- *Cytophaga, Fusobacterium, and Bacteroides*
- Planctomycetes

Non-proteobacteria Gram Negative Bacteria

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These bacterial cells lack a cell wall, thus they do not have a stable shape. They may appear as round bodies or interlacing filaments. 

Mycoplasmas

Pathogenic bacteria are bacteria that can cause infectious disease.

Pathogenic Bacteria

Which of the following bacterial morphologies is characterized by a spiral shape?

Which bacterial morphology is described as rod-shaped?

Which bacterial morphology is described as spherical in shape?

Which bacterial morphology is described as comma-shaped?

The term coccus (plural: cocci) is used to describe prokaryotic cells that possess a round, spherical shape.

Coccus

The term bacillus (plural: bacilli) refers to prokaryotic cells that are rod-shaped, visually resembling long, rounded rectangles. Certain bacilli are also known for their ability to form endospores.

Bacillus

The term vibrio (plural: vibrios) is used to describe prokaryotic cells that are shaped like curved rods, closely resembling a long comma.

Vibrio

The term coccobacillus (plural: coccobacilli) refers to prokaryotic cells that appear as short rods, closely resembling ovals.

Coccobacillus

The term spirillum (plural: spirilla) describes prokaryotic cells that possess a long, spiral shape, visually resembling a corkscrew.

Spirillum

Spirochete

Planctomycetes are a phylum of bacteria that are typically water dwelling. Unlike many bacteria, they reproduce via budding rather than binary fission. A bud separates from the mother cell. Sessile cells are immobile and contain a holdfast appendage that allows them to adhere to surfaces in the water. The sessile cells are able to reproduce.

Planctomycetes

Gram-negative cells possess a cell envelope with a significantly thinner layer of peptidoglycan—no more than about $${}4$$ nm thick—compared to gram-positive cells. Their overall cell envelope structure is highly complex, featuring a periplasmic space and an outer membrane located external to the peptidoglycan layer.

Gram Negative Cell Walls

The *Chlamydia* genus consists of many pathogens. They spread very easily from host to host because they form elementary bodies during their life cycle. These are spore-like which allows *Chlamydia* to be metabolically inactive until they are in a host environment.

*Chlamydia*

This phylum contains gram-negative nonproteobacteria that are linked together because of their similarities in their DNA sequences. They are rod bacteria that are primarily living in anaerobic environments and many of which are fermenters.

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