Myxobacteria, often referred to as “slime bacteria,” are a distinct group of microorganisms predominantly found in soil environments. They are known for their relatively large genomes, with some species possessing over 16 million nucleotides, among the largest bacterial genomes identified. These rod-shaped bacteria exhibit a unique social lifestyle, distinguishing them from many other single-celled organisms. This cooperative behavior allows them to interact and perform complex tasks as a collective.
Myxobacteria typically glide across surfaces, a form of movement that facilitates their social interactions. They are often found in neutral to slightly alkaline soils, with a pH range generally between 6.5 and 8.5, though some species can tolerate more acidic or alkaline conditions. Their ability to move and communicate as a group underpins their remarkable survival and feeding strategies in their natural habitats.
Cooperative Hunting and Swarming
Myxobacteria move and feed cooperatively in what are described as “wolf packs” or swarms. This collective movement is not random; thousands of cells coordinate their gliding motions, forming dynamic multicellular groups. This swarming behavior allows them to expand rapidly over surfaces, increasing their access to nutrients.
When a myxobacterial swarm encounters prey, such as other bacteria or yeast, the group acts together. They penetrate the prey colony and release a variety of extracellular enzymes and other secondary metabolites. These enzymes break down the prey cells, releasing smaller molecules that the myxobacteria can then absorb and utilize. This cooperative digestion is highly efficient because the accumulated enzymes from many cells create a concentrated pool of degradative agents, optimizing the use of available nutrients.
Two distinct motility systems facilitate this coordinated movement in species like Myxococcus xanthus. Adventurous (A) motility drives the movement of individual cells and involves the secretion of slime trails. Social (S) motility, on the other hand, is cell-contact dependent and relies on type IV pili and exopolysaccharides, allowing cells to travel in groups. These systems work together to enable the swarm to spread and effectively overwhelm and digest their food sources.
Surviving Harsh Conditions
Myxobacteria transform to survive nutrient scarcity. Instead of perishing individually, these cells aggregate, forming multicellular structures known as fruiting bodies. This aggregation is a complex developmental process, involving thousands of cells organizing their gliding movements.
Fruiting bodies can vary in shape and color depending on the myxobacterial species, ranging from simple globular mounds to more intricate tree-like structures. Within these fruiting bodies, the vegetative rod-shaped cells differentiate into rounded, thick-walled cells called myxospores. These myxospores are a dormant, resistant form of the bacterium, capable of enduring unfavorable environmental conditions like heat, ultraviolet radiation, and desiccation.
This sporulation process finishes after starvation begins. The formation of myxospores within the protective confines of the fruiting body enhances their ability to survive until more favorable conditions return. When nutrients become available again, these myxospores can germinate, allowing the entire population to emerge together and re-establish a cooperative feeding community.
Myxobacteria’s Value to Science and Medicine
Myxobacteria are valuable in scientific and medical research due to their diverse chemical compounds. They produce many secondary metabolites with biological activities. Over 100 secondary metabolites with over 600 structural variants have been isolated from myxobacterial strains.
Among these compounds are antibiotics, important due to increasing antibiotic resistance. For instance, epothilones, secreted by Sorangium cellulosum, have shown antineoplastic activity, leading to the development of analogs like Ixabepilone, an FDA-approved chemotherapy agent. Other examples include cystobactamids, which inhibit bacterial topoisomerases, and myxovalargin, which has shown activity against Mycobacterium tuberculosis.
Myxobacteria also serve as model organisms for studying bacterial multicellularity. Their complex life cycle, which includes cooperative predation and the formation of multicellular fruiting bodies, provides a unique system to investigate cellular signaling, gene regulation, and cell fate determination in bacteria. Insights gained from studying myxobacterial multicellularity can contribute to a broader understanding of developmental evolution, even extending to more complex organisms.