Bacillales are an order of the bacterial class Bacilli that includes families such as Alicyclobacillaceae, Bacillaceae, Listeriaceae, and Paenibacillaceae. Bacteria of the order exhibit Gram-positive properties and often form endospores, especially under unfavorable conditions. While some are used as probiotics, others are opportunistic or obligate pathogens.
What are bacillales?
Bacilli are a bacterial class of Gram-positive bacteria with low GC content. Parts of the exact systematics are uncertain to date. Nonetheless, the bacterial order Bacillales is included in the class Bacilli. The Bacillales are gram-positive bacteria that mostly occur in rod form. Most representatives of the order are aerobic. The sometimes important characteristic of the individual representatives is their ability to form endospores in the case of food shortage, extreme temperatures or other unfavorable conditions. The genus Bacillus from the bacterial family Bacillaceae gave its name to the order Bacillales. The order is currently understood to include families such as the Alicyclobacillaceae, the Bacillaceae, the Listeriaceae, and the Paenibacillaceae. In addition, the bacterial families Pasteuriaceae, Planococcaceae, Sporolactobacillaceae, Staphylococcaceae and Thermoactinomycetaceae are also included under the order. Different genera have not yet been assigned to any family. These genera include, for example, Exiguobacterium as well as Gemella and Solibacillus. According to analyses of their 16S-rRNA sequence, a close relationship to representatives of the order Bacillales is probable. For this reason, the three genera are assigned to the order for the time being.
Occurrence, distribution, and characteristics
Bacterial families of the order Bacillales usually carry rod shape, but can also turn out as Planococcaceae, for example, coccoid. The representatives of the order are generally aerobic. This means that the metabolism of the microorganisms does not require oxygen. To grow and survive, the individual representatives of the order are thus dependent on an oxygen-rich environment. Representatives such as the family Listeriaceae are partly facultatively anaerobic. They can therefore survive without oxygen if absolutely necessary. Their metabolism changes for this purpose and, if necessary, resorts to other substances for energy production. Some representatives of the Bacillales, for example, also carry out fermentation and resort to glucose or lactate. Still other representatives carry out nitrogen oxidation. The Planococcaceae family in particular possesses the enzymes catalase and oxidase. While many representatives of the order are basically immobile, individual representatives of the family Listeriaceae, for example, are flagellated and thus capable of active locomotion. The order Bacillales is quite diverse with respect to ideal growth conditions. Many families of the order are heat-loving. Some are characterized as acid-loving, such as Alicyclobacillaceae. As different as the preferred environment of the individual families, their distribution and habitat turn out to be. Individuals from the order Bacillales can be found in normal soils as well as in water and air. The genus Bacillus in particular is also a physiological part of the human and animal intestinal flora. Some representatives of the order Bacillales can appear as fruit juice spoilers. The family Paenibacillaceae preferentially colonizes insects and is responsible for a number of insect diseases. Not all, but most families in the order Bacillales form endospores. Endospores are a survival form that bacteria form within an organism or cell. The endospore-forming members of the Bacillales form endospores primarily under unfavorable conditions in order to secure a survival advantage. Endospores are usually relatively resistant to heat, extreme cold, desiccation, radiation, extreme pH, and chemistry.
Importance and function
The species Bacillus subtilis of the genus Bacillales is now used as a bioweapon under certain circumstances. It is a probiotic used against pathogenic prebiotics in the intestine and can curb the growth of bifidobacteria. Representatives of the species possess enzymatic high activity and thus stimulate digestion. In addition, they produce virus-killing interferon.Bacillus subtilis has bactericidal activity in the intestine against Escherichia, Proteus, Salmonella, Klebsiella and Citrobacter, but also Enterobacteria, Streptococcus, Staphylococcus, Clostridium or Pseudomonas. As a component of the physiological intestinal flora, many other representatives of the order Bacillales fulfill similar functions. Thus, the order includes by far not only pathogenic pathogens, but also neutral commensals and even porbiotics that are beneficial to humans. Bacteria of this species prevent diarrheal diseases, protect against intestinal infections with pathogenic agents, and restore normal intestinal flora after antibiotic treatment.
Diseases and ailments
Different families of the order Bacillales include human pathogens. This is especially true for Bacillus. Both apathogenic and obligate pathogenic or opportunistic pathogens are included in this bacterial group. Especially opportunistic pathogens of the species Bacillus cereus or Bacillus stearothermophilus can lead to food poisoning for immunocompromised or otherwise constitutionally compromised people, whereas immunocompromised people do not have to fear infection. An obligate pathogenic species is Bacillus anthracis, which causes what is known as anthrax. Infection can occur through direct contact or consumption of contaminated food. However, inhalation of the spores through the air can also lead to infection. Representatives of the species Bacillus anthracis produce the so-called anthrax toxin. This protein mixture is an exotoxin that the bacteria excrete during infection. After invasion of host cells, the protein mixture destroys cellular tissue. Anthrax is treated with penicillin. In addition, ciprofloxacin, erythromycin, and tetracyclines are available for treatment.
