Alkalihalobacillus clausii

Alkalihalobacillus clausii (synonym Bacillus clausii) is a rod-shaped, motile, and spore-forming bacterium that lives in the soil but is also a natural microbiota of the mammalian gastrointestinal tract. It is classified as probiotic microorganism that maintains a symbiotic relationship with the host organism.^[1] It is currently being studied in relation to respiratory infections^[2] and some gastrointestinal disorders.^[3] Bacillus clausii has been found to produce antimicrobial substances that are active against gram-positive bacteria including Staphylococcus aureus, Enterococcus faecium and Clostridioides difficile.^[1] It is used widely as a probiotic in gastrointestinal conditions to maintain gut health, and is therefore considered a good bacterium. Generally considered safe, Alkalihalobacillus clausii can sometimes cause infections, especially in patients with impaired immunity. Immunocompromised individuals, such as patients with cancer, organ transplants, central venous catheters, or prolonged hospitalization, may develop bacteraemia. Newborn babies and young children are also at risk because of their immature immune systems.^[4] It is sold as an Antidiarrheal under the brand name Erceflora by Sanofi.^[5]

Alkalihalobacillus clausii
Alkalihalobacillus clausii from Enterogermina on a glass slide
Scientific classification
Domain:	Bacteria
Kingdom:	Bacillati
Phylum:	Bacillota
Class:	Bacilli
Order:	Bacillales
Family:	Bacillaceae
Genus:	Alkalihalobacillus
Species:	A. clausii
Binomial name
Alkalihalobacillus clausii (Nielsen et al. 1995) Patel and Gupta 2020
Synonyms
Bacillus clausii Nielsen et al. 1995

This species has been recently transferred into the genus Alkalihalobacillus.^[6] The correct nomenclature is thus Alkalihalobacillus clausii.

History

The strain AO1125 of Alkalihalobacillus clausii originally came from soil in California.^[7]

Genomics

The genome of Alkalihalobacillus clausiiAO1125 was sequenced by researchers using Illumina technology, resulting in 25 contigs and a total length of about 4.3 megabases.^[7] The annotation of the genome revealed genes linked to gut colonization, immune system modulation, and stress resistance.^[7] Each one of these linkages further supports the probiotic role of Alkalihalobacillus clausii.^[7] The analysis also identified antimicrobial resistance (AMR) genes present with low clinical relevance and confirmed the absence of plasmids, suggesting a lowered risk of horizontal gene transfer.^[7]

Probiotic Capabilities

Alkalihalobacillus clausii exists in two different forms: dormant spores and active vegetative cells.^[8] Vegetative cells are sensitive to extreme environments, such as the human gastrointestinal tract. Because of this, only a small amount of vegetative cell probiotics may reach the intestine unless they are administered in capsules or other protective molds.^[8] Spore-forming probiotics have intrinsic resistance, so they can survive the gastrointestinal tract conditions.^[8] After traveling through the tract and reaching the intestine, these spore-forming probiotics can germinate and produce vegetative cells. These cells can then provide beneficial probiotic effects.^[8]

These probiotic properties of A. clausii can help restore gut microbiota composition altered by antibiotic treatment.^[9] A study done on mice with CFX-induced intestinal injury helped determine the mechanism A. clausii uses to do this.^[9]

Metabolic Pathways

Alkalihalobacillus clausii is an spore-forming, obligate aerobic bacterium that demonstrates versatility due to its ability to thrive in alkaline and high salt environments. A. clausii relies on many different metabolic pathways to manage variability in its environmental factors (pH, nutrient availability, salinity etc.).^[10] It is able to catabolize many different organic compounds as both a carbon and energy source, such as carbohydrates, amino acids, and organic acids.^[10]

A. clausii is classified as a chemooroganoheterotroph, utilizing Glycolysis, the Pentose Phosphate Pathway, and the Tricarboxylic Acid Cycle for carbohydrate metabolism.^[10] A. clausii also uses a Futile Cycle to produce pyruvate and NADPH/NADH through a Malic Enzyme, allowing for metabolic and cellular flexibility.^[10][11]