Myxococcus

Myxococcus is a genus of bacteria in the family Myxococcaceae. Myxococci are Gram-negative, spore-forming, chemoorganotrophic, obligate aerobes. They are elongated rods with rounded or tapered ends, and they are nonflagellated. The cells utilize gliding motility to move and can predate other bacteria. The genus has been isolated from soil.

Myxococcus
Fruiting bodies of M. xanthus
Scientific classification
Domain:	Bacteria
Kingdom:	Pseudomonadati
Phylum:	Myxococcota
Class:	Myxococcia
Order:	Myxococcales
Family:	Myxococcaceae
Genus:	Myxococcus Thaxter 1892
Type species
Myxococcus rubescens (Cohn 1875) Jahn 1911
Species
See text
Synonyms
Myxococcus section "Simplices" Jahn 1911 Myxococcus section "Stipitatae" Jahn 1911 Pyxidicoccus corrig. Reichenbach 2007

At least eleven species had been identified with confidence by late 2020 and each had been characterised to some extent. As well as using traditional biochemical tests, strains of some species had been compared using whole genome sequences. This approach has provided evidence that the genus, like most bacterial genera, has a core set of genes found in all members of the genus, along with others that are confined to particular species. The identity of Myxococcus species therefore continues to change. An example where taxonomy may be changed is that comparisons of genome sequences and biochemical tests indicated that M. xanthus and M. virescens were not distinguishable.^[1][2]

One notable characteristic of Myxococcus is its formation of fruiting bodies. Myxococcus are known to form fruiting bodies using chemical signals. The cells communicate with each other, and in response to stress factors, most often starvation, begin to form fruiting bodies. These fruiting bodies then allow Myxococcus to transform into round spores resistant to the environment.^[3] The genetic programs underlying fruiting body formation in the Myxococci exhibit an unexpected level of plasticity, strongly suggesting that the genetic program underlying fruiting body formation in various Myxococci is not conserved, leading to diverse reactions in all Myxococcus species.^[4] Rather than chemotaxis used by other microorganisms for cell-cell communication, Myxococcus, specifically M. xanthus, a species of Myxococcus, has been found to use direct cell-to-cell communication to form fruiting bodies.^[3]

In addition, Myxococcus prey interacts with one another by sending quorum signals using acyl homoserine lactones (AHLs). It was discovered that AHLs increased some Myxococcus colonies' predatory behavior and growth rates. Therefore, the predatory behavior of these Myxococcus bacteria appears to be enhanced by the presence of xenic quorum signaling molecules. Some Myxococcus bacteria employ AHLs as indicators of nearby prey, possibly listening in on talks between prey creatures in the wild.^[5]

This cooperation between different individual Myxococcus allows them to act as a singular organism and perform functions as such, including but not limited to homeostasis repair. While fruiting body development occurs through the Myxococcus genus, it can take on a variety of structures, and dome-shaped mounds have been observed in some species.^[6] Social interactions are major in the myxobacteria's life cycle. In significant groupings compared to wolf packs, cells prey on other bacteria during vegetative growth. When starved, cells produce a macroscopic fruiting body dense with spores. The current state of knowledge on cell-cell signaling during development is reflected in these behavioral activities.^[7]

Myxococcus is a single celled predatory bacteria that are facultative bacteria. Myxococcus are social microbes and often seen as exhibiting “wolf-pack” behavior.^[8] They are able to communicate with each other via quorum sensing. Myxococcus are seen as predatory microbial communities because of their behavior. They are able to form several distinct multicellular structures. Myxococcus are found in soil. Single cells combine and form large clusters using quorum sensing. When nutrients are unavailable, these cells become fruiting bodies that contain approximately 50,000 cells.^[9] One study found that after placing the bacteria in starving conditions they aggregated into mounds of 100,000 cells.^[10]

Myxococcus is notable for the way it preys, making it unusually akin to wolf packs. Bacteria behaving and preying in ways similar to advanced organisms is unique, and it is one of the defining characteristics of Myxococcus. While bacteria typically rely on solitary mechanisms to prey, Myxococcus preys in groups, coordinating their behaviors and actions with other members of the group. By doing so, Myxococcus can lyse other bacteria and organisms it would otherwise be unable to. For these reasons, Myxococcus is often considered to be “wolf-like” because, similar to wolf packs, by working together in a swarm, Myxococcus can achieve things it would not be able to achieve working alone. The swarming behavior of Myxococcus is also similar to that of wolf packs.

Myxococcus quorum sensing

Myxococcus is unique among prokaryotes in the way it socializes. Through tactics such as quorum sensing, Myxococcus is able to regulate the movement of the group when they are in “packs,” coordinate attack plans to prey, and carry out the construction of fruiting bodies in an efficient manner. The swarming mobility of Myxococcus is vital in being able to efficiently behave as a pack and coordinate with others. Interestingly, Myxococcus has two main mobility systems that coordinate its swarming. The first is social mobility (S), which requires cell-to-cell communication in order to function. The second is adventurous mobility (A), which allows each individual to move on their own. Using both of these mobility systems in tandem, Myxococcus is able to efficiently formulate a group that moves and behaves as one but is composed of several independent members. These two swarming mobility systems are crucial in allowing Myxococcus to behave in the characteristic way we know it to – like a “wolf pack." ^[11]

When Myxococcus requires nutrients or is in a sparse environment, it coordinates the construction of fruiting bodies. The construction of fruiting bodies is a highly organized group effort by Myxococcus, which would not be possible if it were acting alone. Fruiting bodies are cellular structures that help protect Myxococcus from the environment, allowing the group the survive harsh conditions. This is akin to a wolf pack huddling close together and setting up camp for the night when conditions are too harsh to continue hunting. There are three distinct phases in constructing a fruiting body. First, the members of the group start to immobilize. Then, they move and aggregate together in a highly coordinated manner. Lastly, they eventually mature into a structure – a fruiting body. This process demonstrates complex social coordination, as the cells must communicate chemically and be aware of each other and the outside environment at all times.^[12]

Myxococcus are able to prey^[13] and thrive on soil bacteria, plant pathogens, cyanobacteria. Multiple studies have shown that under laboratory conditions Myxococcus can thrive off these prey species.^[13] Myxococcus are able to prey using gliding motility. There are two ^[10] of these systems: (i) social (S)-motility and adventurous (A)-motility. Social motility is based on IV pili and adventurous motility is based on slime-secretion.

Myxococcus is a soil-dwelling bacterium that can aggregate into fruiting bodies when food is scarce. This process is regulated by quorum sensing, a type of cell-to-cell communication that allows bacteria to coordinate their behavior in response to population density.^[14]

In Myxococcus, quorum sensing is mediated by two signaling molecules: A-factor and C-signal. A-factor is a small, diffusible molecule that is produced by all cells in the population. When the concentration of A-factor reaches a certain threshold, it binds to receptors on the surface of cells and triggers a cascade of events that leads to aggregation.^[15]

C-signal is a larger, cell-surface protein that is not diffusible. It is produced by a subset of cells in the population and binds to receptors on the surface of other cells. This interaction triggers a cascade of events that leads to the formation of fruiting bodies. Quorum sensing is essential for the survival of Myxococcus. By aggregating into fruiting bodies, the bacteria can protect themselves from predators and desiccation. They can also produce spores that can survive in harsh environments until conditions improve. Quorum sensing is a complex process that is still not fully understood. However, it is clear that it plays an important role in the life cycle of Myxococcus and other bacteria.^[16][17]

In addition to its role in aggregation and fruiting body formation, quorum sensing also regulates other aspects of Myxococcus development, such as motility, chemotaxis, and virulence. Quorum sensing is also used by Myxococcus to communicate with other bacteria, such as its prey.^[18] This allows the bacteria to coordinate their activities and improve their chances of survival.

Myxococcus secretes antibiotics and bacteriolytic enzymes to kill their prey. Because of this, there has been speculation of using Myxococcus as novel antibacterial strategies.^[13]

Sources

• "Myxococcus". The Encyclopedia of Life.

Phylogeny

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN)^[19] and National Center for Biotechnology Information (NCBI)^[20]

16S rRNA based LTP_10_2024[21][22][23]

120 marker proteins based GTDB 09-RS220[24][25][26]

Myxococcus Pyxidicoccus fallax M. fulvus M. dinghuensis M. stipitatus Pyxidicoccus xibeiensis Pyxidicoccus trucidator M. guangdongensis M. qinghaiensis M. eversor[1] M. llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogochensis [1] M. macrosporus M. vastator[1] M. virescens M. xanthus

Myxococcus M. dinghuensis Wang et al. 2023 M. guangdongensis Wang et al. 2023 M. fulvus (Cohn 1875) Jahn 1911 "M. landrumus" Ahearne et al. 2023 M. stipitatus Thaxter 1897 M. llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogochensis Chambers et al. 2021 M. eversor Chambers et al. 2021 M. qinghaiensis Wang et al. 2023 Pyxidicoccus fallax corrig. Reichenbach 2007 Pyxidicoccus xibeiensis Wang et al. 2023 Pyxidicoccus trucidator Chambers et al. 2020 "Pyxidicoccus caerfyrddinensis" Chambers et al. 2020 "Pyxidicoccus parkwaysis" Ahearne et al. 2023 "M. hansupus" Sharma et al. 2016[2] M. macrosporus (Krzemieniewska & Krzemieniewski 1926) Zahler & McCurdy 1974 non Zukal 1897 M. vastator Chambers et al. 2021 M. virescens Thaxter 1892 M. xanthus Beebe 1941

See also

• List of bacterial orders
• List of bacteria genera