Image source: Diane Montpetit, Food Research and Development Centre, Agriculture and Agri-Food Canada
Bacteria; Firmicutes; Bacilli; Bacillales; Bacillaceae; Bacillus; Bacillus subtilis; Bacillus subtilis subsp. subtilis
Chromosome: 4,214,630 bp
Plasmid p1414: 7,949 bp
Plasmid pBC16: 4,630 bp
Plasmid pIM13: 2,246 bp
Plasmid pTA1015: 5,807 bp
Plasmid pTA1040: 7,837 bp
Plasmid pTA1060: 8,737 bp
Bacilli are an extremely diverse group of bacteria that include both the causative agent of anthrax (Bacillus anthracis) as well as several species that synthesize important antibiotics. In addition to medical uses bacillus ,spores, due to their extreme tolerance to both heat and disinfectants, are used to test heat sterilization techniques and chemical disinfectants. Bacilli are also used in the detergent manufacturing industry for their ability to synthesize important enzymes.
The sequence for the genome of Bacillus subtilis was completed in 1997 and was the first published sequence for a single-living bacterium. The genome is 4.2 Mega-base pairs long with with 4100 protein-coding regions. Bacillus subtilis has a plant growth promoting rhizobacterium shown to synthesize antifungal peptides. This ability has lead to the use of B. subtilis in biocontrol. B. subtilis has been shown to increase crop yields, although it has not been shown whether this is because it enhances plant growth, or inhibits disease growth.
The genome of Bacillus anthracis is 5,227,293 base pairs long with 5,508 predicted protein-coding regions. The genome of B. anthracis is highly homologous with the genomes of both B. cereus and B. thuringiensis which have also been sequenced. The genome of B. anthracis has only 141 proteins that do not have a match in the protein set of B. cereus. Almost all of the virulence factors associated with anthrax are coded on its two plasmids and, surprisingly, almost all of these genes have homologues in B. cereus. This suggests that these virulence-enhancing genes are not specifically unique to Bacillus anthracis, but rather are part of the common array of genes of the B. cereus group (of which B. anthracis, B. cereus, and B. thuringiensis are all a part). B. anthracis also seems to have a decreased capacity for the extensive carbohydrate metabolism seen in B. subtilis, but possesses the genes for the cleavage of extracellular chitin and chitosan, which confirms its close relationship with the insect pathogen B. thuringiensis.
Bacilli are rod-shaped, Gram-positive, sporulating, aerobes or facultative anaerobes. Most bacilli are saprophytes. Each bacterium creates only one spore, which is resistant to heat, cold, radiation, desiccation, and disinfectants. Bacilli exhibit an array of physiologic abilities that allow them to live in a wide range of habitats including many extreme habitats such as:desert sands, hot springs, and Arctic soils. Species in the genus Bacillus can be thermophilic, psychrophilic, acidophilic, alkaliphilic, halotolerant, or halophilic and are capable at growing at pH values, temperatures, and salt concentrations where few other organisms can survive.
Due to the metabolic diversity in the genus Bacillus, bacilli are able to colonize a variety of habitats ranging from soil to insects, to humans. Bacillus thuringiensis parasitizes insects, and is commercially used form pest control. Although the most well known of the bacilli are the pathogenic species, most bacillus are saprophytes that make their living off of decaying matter. Still others, namely Bacillus subtilis, inhabit the rhizosphere, which is the interface between plant roots and the surrounding soil. The plants roots and associated biofilm can have a significant effect of on the chemistry of the soil, creating a unique environment.
It has recently been shown that Bacillus subtilis engages in cannibalism. They use cannibalism as the easy way out in extreme cases. For survival in harsh environments, bacilli can form spores, but it is very costly to them energy-wise. An easier way, is for the bacteria to produce antibiotics that destroy neighboring bacilli, so that their contents may be digested allowing for the survival of a few of the bacteria. Essentially, what they are doing is snacking on their fellow bacilli, to tide them over, hoping for the environment to pick back up.
Bacilli cause an array of infections from ear infections to meningitis, and urinary tract infections to septicemia. Mostly they occur as secondary infections in immunodeficient hosts or otherwise compromised hosts. They may exacerbate previous infection by producing tissue-damaging toxins or metabolites that interfere with treatment.
The most well known disease caused by bacilli is anthrax, caused by Bacillus anthracis. Anthrax has a long history with humans. It has been suggested that the fifth and sixth plagues of Egypt recorded in the Bible (the fifth attacking animals, the sixth, known as the plague of the boils, attacking humans). In the 1600s anthrax was known as the "Black bane" and killed over 60,000 cows. Anthrax has more recently been brought to our attention as a possible method for bioterrorism. The recent anthrax mailings have brought acute public attention to the issue and sparked extensive research into the devastating disease.
Anthrax is primarily a disease of herbivores who acquire the bacterium by eating plants with dust that contains anthrax spores. Humans contract the disease in three different ways. Cutaneous anthrax occurs when a human comes into contact with the spores form dust particles or a contaminated animal or carcass through a cut or abrasion. Cutaneous anthrax accounts for 95% of anthrax cases worldwide. During a 2-3 day incubation period the spores germinate, vegetative cells multiply, and a papule develops. Over the following days the papule ulcerates, dries and blackens to form the characteristic eschar. The process is painless unless infected with another pathogen.
Gastrointestinal anthrax is contracted by ingesting contaminated meat. It occurs in the intestinal mucosa when the organisms invade the mucosa through a preexisting lesions. It progresses the same way as cutaneous anthrax. Although it is extremely rare in developed countries it has a very high mortality rate.
Pulmonary anthrax is the result of inhaled spores that are transported to the lymph nodes where they germinate and multiply. They are then taken into the blood stream and lymphatics culminating in systemic arthritis which is usually fatal.
Institut Pasteur, Unite de Biochimie Microbienne, Paris, France. firstname.lastname@example.org
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