Asymmetric bacteria are

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

that undergo "non-symmetrical" life cycles. This especially includes those that differentiate temporally, such as

prosthecate bacteria Prosthecate bacteria are a non-phylogenetically related group of Gram-negative bacteria that possess appendages, termed ''prosthecae''. These cellular appendages are neither pili nor flagella, as they are extensions of the cellular membrane and ...

History

Cell division asymmetries have appeared alongside the evolution of complex developmental processes. While bacteria were historically considered symmetric simple cells, this idea has been overturned by novel technology and observation techniques. However, asymmetric bacteria remain difficult to detect. Asymmetrical growth aids in determining the age of bacteria, because it gives rise to an ''old pole'', or region of inert cell wall material found at the ends of a rod-shaped bacterial cell. Following the "old pole" of the cell wall material allows an observer to create a bacterial lineage.

Types of asymmetry

Bacteria exhibit three different types of asymmetry: conditional asymmetry, reproductive asymmetry, and morphological asymmetry. Conditional asymmetry is well defined in the case of

endospore An endospore is a dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Bacillota. The name "endospore" is suggestive of a spore or seed-like form (''endo'' means 'within'), but it is not a true spore (i.e., not ...

formation, which is triggered by stressful environmental conditions such as increased heat, pH change, and nutrient depletion. This type of asymmetry is usually seen in

Bacilli Bacilli is a taxonomic class of bacteria that includes two orders, Bacillales and Lactobacillales, which contain several well-known pathogens such as ''Bacillus anthracis'' (the cause of anthrax). ''Bacilli'' are almost exclusively gram-posit ...

and

Clostridia The Clostridia are a highly polyphyletic class of Bacillota, including '' Clostridium'' and other similar genera. They are distinguished from the Bacilli by lacking aerobic respiration. They are obligate anaerobes and oxygen is toxic to them. S ...

. Reproductive asymmetry is classically linked to bacterial budding, where a mother cell concentrates

cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mec ...

material to one area and a daughter cell begins to bud from that thickening. Cell growth which gives rise to reproductive asymmetry occurs in three phases: stalk elongation, daughter cell elongation, and septum formation. Morphological asymmetry is classified by polar elongation. In this type of asymmetrical growth, the daughter cell receives most of the new cell wall material.

Examples

* ''

Bacillus subtilis ''Bacillus subtilis'', known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus '' Baci ...

'' * ''

Caulobacter crescentus ''Caulobacter crescentus'' is a Gram-negative, oligotrophic bacterium widely distributed in fresh water lakes and streams. The taxon is more properly known as ''Caulobacter vibrioides'' (Henrici and Johnson 1935). ''C. crescentus'' is an impo ...

References

Bacteria {{bacteria-stub