Alicyclobacillus

Alicyclobacillus is a genus of Gram-positive, endosporenbildender soil bacteria. Several types of lipids contained in the biomembrane unusual fatty acids, which are referred to as omega- alicyclic. The genus name refers to these fatty acids. Alicyclobacillus species are thermophilic and they also grow at low pH values. They are involved in the bacterial spoilage of fruit juices and thus represent a potential problem with their production dar.

Features

Appearance

Alicyclobacillus is a genus of Gram-positive bacteria, in older cultures they are gram variable. The cells are in the form of rods having a diameter of 0.3-0.8 microns and a length of 2.0-4.5 microns. You can move actively, they are motile. Under adverse environmental conditions, they form endospores than Überdauerungsformen. The formation of endospores is independent of whether there is enough oxygen present. The endospores of some Alicyclobacillus species are very resistant to heat and survive a brief heating to 92 ° C. This is problematic for the fruit juice industry.

Growth and metabolism

Alicyclobacillus grows strictly aerobic, so it can only multiply when oxygen is present. Alicyclobacillus species are thermophilic ( " heat- loving" ) and acidophilic ( "acid- loving" ). To grow at temperatures between 20 and 70 ° C, the optimum growth temperature between 35 and 60 ° C. The optimum pH is 2.0 to 6.0.

Chemotaxonomic features

Although the Firmicutes actually a lower GC content in the bacterial DNA is typical, this is Alicyclobacillus species rather high, 48.7 to 62.7 mole percent. The major quinone is menaquinone MK type - seventh The lipids in the biomembrane have unusual fatty acids, called Omega -alicyclic ( ω -alicyclic ) and were included in the genus name. The Greek letter Omega refers to the last position in the carbon chain. The use of lower-case Greek letters as locant is common in fatty acids. Alicyclic compounds are cyclic hydrocarbons. The rings in the structure of these fatty acids are usually made six or seven carbon atoms, such ring systems are referred to as cyclohexane or cycloheptane.

In this special feature Alicyclobacillus cycloheptanicus was assigned the species name. In this type fatty acids are found mainly in the cell membrane with a terminal cycloheptane: Omega - Cycloheptylundecansäure ( ω - cycloheptane C18: 0), omega- Cycloheptyltridecansäure ( ω - cycloheptane C20: 0) and omega- cycloheptyl -alpha hydroxyundecansäure ( ω - cycloheptane C18: 0 2 -OH). In A. acidocaldarius and A. acidiphilus the omega- alicyclic fatty acids dominated, with a ring of six carbon atoms: Omega - Cyclohexylundecansäure ( ω - cyclohexane C17: 0) and omega- Cyclohexyltridecansäure ( ω - cyclohexane C19: 0).

With the discovery of the species A. pomorum the description of typical fatty acids in 2003 was expanded: In addition to the omega- alicyclic fatty acids and straight-chain and branched-chain, saturated fatty acids are present. Typical examples of the latter are fatty acids with the abbreviations iso- C15: 0 (iso- pentadecanoic acid ), anteiso - C15: 0 ( anteiso - pentadecanoic acid ), iso- C16: 0 (iso- hexadecanoic acid ), iso- C17: 0 (iso - heptadecanoic acid ) and anteiso - C17: 0 ( anteiso heptadecanoic ). The fatty acids with 15 and 17 carbon atoms also still belong to the odd-numbered fatty acids.

Occurrence

The habitat of several Alicyclobacillus species is found at extreme locations. The first Alicyclobacillus strain 1967 isolated from hot springs in Japan. In the following years, both the water as well as the soil at sites were examined, can where thermophilic and acidophilic bacteria to grow. The bacteria discovered were later assigned to the genus Alicyclobacillus. Also from soils that are not available in conjunction with thermal springs, Alicyclobacillus species could be isolated, eg from arable soils. Until 1982 Alicyclobacillus has been associated with spoilage of fruit juices, since several species have been found in acidic drinks, such as A. acidoterrestris in apple juice and passion fruit juice and A. acidiphilus. The 2007 discovered species A. contaminans and A. fastidiosus were isolated from orange juice or apple juice. In Brazil, carried out microbiological checks of orange trees and the soil in which they grow, showed the presence of Alicyclobacillus or bacterial spores. From the ground as natural habitat they can be transferred to the fruit and thus may enter in the manufacturing process of the fruit juice. Even in liquid sugar one species (A. sacchari ) was discovered.

System

The first Alicyclobacillus strain was isolated from hot springs in 1967 and named for further studies in 1971 as a new species Bacillus acidocaldarius. Even more newly discovered species of the genus Bacillus were initially assigned. Based on 16S rRNA study Alicyclobacillus 1992 has been proposed as a new genus. Two bacterial strains, which were previously assigned to the genus Sulfobacillus were found to be tolerans A. and A. disulfidooxidans 2005 on Alicyclobacilli. 2007 resulted in phylogenetic studies of 146 bacterial strains were isolated from fruit juices, their raw materials and environmental samples, the first description of six new species.

The genus Alicyclobacillus in the family of Alicyclobacillaceae is made to the order Bacillales in the Department of Firmicutes. From the genus following species are known (as of 2014):

• Alicyclobacillus acidiphilus Matsubara et al. 2002
• Alicyclobacillus acidocaldarius ( Darland & Brock 1971) Wisotzkey et al. 1992 emend. Goto et al. 2006 ( the type species of the genus ) Alicyclobacillus acidocaldarius subsp. acidocaldarius ( Darland & Brock 1971) Nicolaus et al. 2002
• Alicyclobacillus acidocaldarius subsp. rittmannii Nicolaus et al. 2002

Industrial importance

Alicyclobacilli are particularly interesting, as usual pasteurization process not disable the spores (92 ° C for 10 seconds) for the fruit juice industry. The high temperatures lead to spore germination. If Alicyclobacillus present as an impurity in a product, a disinfectant -like smell and / or taste developed by the metabolic product of guaiacol. Also similar compounds, the halogenated phenols are produced as unwanted sensory components ( off-flavor) of them. The product is optically correct, that is, it is not form gases which expand the package and there is no discoloration instead. A contamination with Alicyclobacillus is not dangerous for humans. Alicyclobacilli have been associated with spoilage of pears, mangoes and grape juice, and fruit juice blends and products made from tomatoes.

The species A. acidoterrestris is considered as the most important spoilage organisms of the genus Alicyclobacillus, however, were A. acidocaldarius, A. and A. pomorum Herbarius also isolated from spoiled fruit juice products. Other species that were found in acidic drinks that contain A. acidiphilus, A. and A. contaminans fastidiosus.

Fruit juice manufacturers are working under the assumption that bacterial spores germinate not at a pH below 4.6, and that acid- tolerant organisms are not very heat resistant. With these assumptions, a pasteurization is carried out at low temperatures. Today it is possible to detect the pathogen early in the manufacturing process using real - time PCR and adapt to a positive reaction towards the process. Alicyclobacillus is thus an important microorganism in the quality control of the fruit juice industry. The importance of Alicyclobacillus spoilage than has led some researchers to move, to use A. acidoterrestris as a reference organism for the development of a pasteurization process for highly acidic foods. Similarly, the Dezimalreduktionszeit ( " Absterbezeit " at a certain temperature ) of Clostridium botulinum was used to develop the sterilization process for little acidic, bottled canned foods.