Priestia megaterium
Priestia megaterium is a rod-like, Gram-positive, mainly aerobic, spore forming bacterium found in widely diverse habitats. It has a cell length up to 100 μm and a diameter of 0.1 μm, which is quite large for bacteria. The cells often occur in pairs and chains, where the cells are joined by polysaccharides on the cell walls.
In the 1980s, prior to the use of Bacillus subtilis for this purpose, P. megaterium was the main model organism among Gram-positive bacteria for intensive studies on biochemistry, sporulation, and bacteriophages. Recently, its popularity has started increasing in the field of biotechnology for its recombinant protein-production capacity.
Characteristics
P. megaterium grows at temperatures from 3 to 45 °C, with the optimum around 30 °C. Some isolates from an Antarctic geothermal lake were found to grow at temperatures up to 63 °C. It has been recognized as an endophyte and is a potential agent for the biocontrol of plant diseases. Nitrogen fixation has been demonstrated in some strains of P. megaterium.P. megaterium has been an important industrial organism for decades. It has been used to produce enzymes such as amylases used in the baking industry, glucose dehydrogenase used in glucose blood tests, enzymes for modifying corticosteroids, and several amino acid dehydrogenases. Furthermore, it is used for the production of pyruvate, vitamin B12 and molecules with fungicidal and antiviral properties including penicillin. Several of these bioactive compounds are cyclic lipopeptides, belonging to the surfactin, iturin, and fengycin lipopeptide families, which are also produced by several other Bacillus species.
P. megaterium is known to produce poly-γ-glutamic acid. The accumulation of the polymer is greatly increased in a saline environment, in which the polymer comprises largely of L-glutamate. At least one strain of P. megaterium can be considered a halophile, as growth on up to 15% NaCl has been observed.
Phylogenetically, based on 16S rRNA, P. megaterium is strongly linked with B. flexus, the latter distinguished from P. megaterium a century ago, but only recently confirmed as a different species. P. megaterium has a complex plasmid content as well as some phenotypic and phylogenetic similarities with pathogens B. anthracis and B. cereus, although itself being relatively harmless.
Isolation
P. megaterium is ubiquitous in the environment. In addition to being a common soil bacterium and an endophyte, it can be found in various foods and on a variety of surfaces, including clinical specimens, leather, paper, stone etc. It has also been isolated from cattle feces, emperor moth caterpillars, and greater wax moth frass.History of the name
The species was described by de Bary in 1884, who called it Bacillus megaterium, but did not give an etymology. However, some subsequent authors called it B. megatherium assuming the name was incorrectly spelled. This trend continues as many scientists still use the name B. megatherium, sowing confusion.The name P. megaterium is a nominative noun in apposition and is formed from the Greek adjective mega, meaning "great", and a second word of unclear etymology. Three hypotheses of the epithet "megaterium" are possible:
- unintentional orthographic error, whereas it should have been megatherium, from therion, to mean "great beast".
- a contraction of "megabacterium" as speculated by Rippel in given the fact that de Bary called the bacterium with the nickname Grosstier or Grossvich
- stems from teras, teratos which could be interpreted to mean "great monster".
The etymology listed in LPSN is, despite being not quite correct, a fusion of the first and third interpretation Gr. adj. megas, large; Gr. n. teras -atis, monster, beast; N.L. n. megaterium, big beast.
The species name megaterium has been applied to other genera.