''Exiguobacterium aurantiacum'' is a

Gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. The Gram stain is ...

alkaliphilic Alkaliphiles are a class of extremophilic microbes capable of survival in alkaline ( pH roughly 8.5–11) environments, growing optimally around a pH of 10. These bacteria can be further categorized as obligate alkaliphiles (those that require hig ...

halotolerant Halotolerance is the adaptation of living organisms to conditions of high salinity. Halotolerant species tend to live in areas such as hypersaline lakes, coastal dunes, saline deserts, salt marshes, and inland salt seas and springs. Halophiles are ...

, and non-spore-forming bacterium''.'' ''

Exiguobacterium ''Exiguobacterium'' is a genus of bacilli and a member of the low GC phyla of Bacillota. Collins'' et al''. first described the genus ''Exiguobacterium ''with the characterization of ''E. aurantiacum'' strain DSM6208T from an alkaline potato pr ...

spp.'' are

facultative anaerobes A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent. Some examples of facultatively anaerobic bacteria are ''Staphylococcus' ...

that have been isolated from a broad range of environments with ''Exiguobacterium aurantiacum,'' the type species, being isolated from alkaline potato-processing effluent in 1980. ''E. aurantiacum'' has been evaluated for use in

bioremediation Bioremediation broadly refers to any process wherein a biological system (typically bacteria, microalgae, fungi in mycoremediation, and plants in phytoremediation), living or dead, is employed for removing environmental pollutants from air, wate ...

and as a source for natural pigments. Two case studies have associated ''E. aurantiacum'' with infections in humans.

Name and classification

The name ''Exiguobacterium aurantiacum'' derives from the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

''exiguus'' meaning "small" or "slender" and ''aurantiacus'' meaning "orange-colored". ''Exiguobacterium'' is one of 122 genera within the ''

Bacillaceae Bacillaceae, from Latin "bacillus", meaning "little staff, wand", are a family of gram-positive, heterotrophic, rod-shaped bacteria that may produce endospores. Motile members of this family are characterized by peritrichous flagella. Some Baci ...

'' family. As of 2024, the ''Exiguobacterium'' genus now hosts 19 species recognized by the International Code of Nomenclature of Prokaryotes (

ICNP The International Code of Nomenclature of Prokaryotes (ICNP) or Prokaryotic Code, formerly the International Code of Nomenclature of Bacteria (ICNB) or Bacteriological Code (BC), governs the scientific names for Bacteria and Archaea.P. H. A. Sneath ...

History

The classification, ''Exiguobacterium aurantiacum,'' was first assigned in 1983 by Collins ''et al.'' after five alkaliphilic bacteria were isolated from potato-processing effluent by Gee ''et al.'' in 1980. The first genome was made available in 2014 by the U.S. Department of Energy

Joint Genome Institute The Joint Genome Institute (JGI) is a scientific user facility for integrative genomic science at Lawrence Berkeley National Laboratory. The mission of the JGI is to advance genomics research in support of the United States Department of Energy ...

. The ''E. aurantiacum'' DSM 6208 genome is composed of 3.04 Mbp with a

GC content In molecular biology and genetics, GC-content (or guanine-cytosine content) is the percentage of nitrogenous bases in a DNA or RNA molecule that are either guanine (G) or cytosine (C). This measure indicates the proportion of G and C bases out of ...

of 53%. Of note, the genome was found to have 90 transposases and two cold shock genes.

Description

''Exiguobacterium aurantiacum'' cells are pleomorphic, ranging from (~3.2 μm) rods in exponential phase to short (~1.2 μm)

coccobacilli Bacterial cellular morphologies are the shapes that are characteristic of various types of bacteria and often key to their identification. Their direct examination under a light microscope enables the classification of these bacteria (and archaea ...

in stationary phase. Cells are gram-positive, motile, and do not form spores. ''E. aurantiacum'' is classified as a facultative anaerobe able to grow on a range of sugars including, but not limited to, glucose, sucrose, and galactose. Colonies grown aerobically on Van Niel's Yeast Agar are glossy with a honey-orange pigment.

Application

''Exiguobacterium aurantiacum'' cells contain a bright orange

carotenoid Carotenoids () are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, archaea, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, corn, tomatoes, cana ...

pigment that has been evaluated as a potential natural pigment source in industry. ''E. aurantiacum'' has also been evaluated for its ability to degrade n-alkanes from

diesel Diesel may refer to: * Diesel engine, an internal combustion engine where ignition is caused by compression * Diesel fuel, a liquid fuel used in diesel engines * Diesel locomotive, a railway locomotive in which the prime mover is a diesel engine ...

. Thus, ''E. aurantiacum'' could be used for bioremediation in oil-contaminated environments. Additionally, ''E. aurantiacum'' has been found to produce a thermostable protease that functions in alkaline environments.

Opportunistic infections

''Exiguobacterium aurantiacum'' has been associated with bacteremia in one case study after it was isolated from six human patients with three of the patients being in an immunocompromised state. Prior to this case study, ''E. aurantiacum'' was linked to one other infection, a case of

periodontitis Periodontal disease, also known as gum disease, is a set of inflammatory conditions affecting the tissues surrounding the teeth. In its early stage, called gingivitis, the gums become swollen and red and may bleed. It is considered the main c ...

, in 2003.

References

Bacillaceae Bacteria described in 1984 {{Bacilli-stub