Bacillus safensis

Bacillus safensis It is an endophytic bacterium and rhizobacterium with promising potential in the biological control of phytopathogens. It acts as a biocontrol agent and plant growth promoter. It is isolated from diverse environments, including agricultural soils, rhizospheres, and even spacecraft surfaces. It has been studied for its ability to inhibit pathogenic fungi and bacteria, reduce the use of chemical fertilizers, and improve plant tolerance to abiotic stresses.

Domain: B

Kingdom: Bacillati

Division: Bacillota (formerly Firmicutes)

Class: Bacilli

Order: Bacillales

Family: Bacillaceae

Genre: Bacillus

Species: Bacillus safensis Satomi et al. 2006

Year of description: 2006 (year of formal description and publication of the species; agricultural applications intensified from 2010 onwards, with endophytic isolates).

Patent numbers: CN118620795, CN117701431, IN202121018803, EP4265111 and others.

Background of knowledge

It was discovered in 2006 by Satomi et al., with 13 isolated cell lines from the surfaces of spacecraft and assembly facilities at the Kennedy Space Center (Florida) and Jet Propulsion Laboratory (California), using cleanroom swab techniques. The name derives from the JPL's "Spacecraft Assembly Facility" (SAF).

Cell lines were accidentally transported to Mars in 2004 by the Opportunity and Spirit rovers, raising concerns about planetary contamination.

Subsequently, isolates from rhizosphere soils (e.g., cumin rhizosphere in the Gujarat desert, India, in 2010) and agricultural soils (India, Egypt, Malaysia) expanded their use for agriculture.

Genomic studies (e.g., VK lineage, 2012) have revealed genes for 1-aminocyclopropane-1-carboxylate deaminase (ACCD), boosting applications in biofertilizers.

Since 2015, Chinese and European patents have registered formulations for biocontrol, with advances in 2022-2024 for fertilizer reduction in tomatoes and growth promotion.

Mode of action

Bacillus safensis It acts through multiple mechanisms:

• Production of antimicrobial compounds (e.g., lipopeptides, enzymes such as inulase and lipase) that inhibit fungal pathogens (e.g., Botrytis cinerea, Fusarium spp.) and bacteria through competition for nutrients, cell lysis, and induction of systemic resistance (SRI).

• Promotes plant growth through the production of phytohormones (auxins, gibberellins) and ACCD, reducing ethylene and improving tolerance to salinity, heavy metals, and hydrocarbons.

• Endophytic/rhizospheric colonization, phosphate solubilization, and indirect nitrogen fixation.

Spores resist UV rays, hydrogen peroxide, and environmental extremes, ensuring persistence in the field.

Biological aspects

Bacillus safensis It is a Gram-positive, rod-shaped bacterium (0,5 - 0,7 μm in diameter x 1,0 - 1,2 μm in length), forming resistant endospores, aerobic chemoheterotrophic and motile by polar flagella. Mesophilic (optimal growth at 10 - 50 ºC, pH 5,6 - 8,0, salinity 0 - 14% NaCl), with strains tolerant to extreme conditions (UV, low humidity, microgravity).

Typical genome: ~3,68 Mbp, 41-46% GC, ~3.900 protein-coding genes, including ACCD for ethylene reduction, hydrolytic enzymes (lipase, inulase), and genes for biosurfactants.

Lineages such as FO-36b form undulate circular colonies; it does not grow below 4°C or above 55°C. Phylogeny close to B. pumilus (99,5% similarity in 16S rRNA), differentiated by gyrA/gyrB sequences.

Ecological aspects

It is found in diverse niches: rhizosphere soils (e.g., cumin in deserts, asparagus in botanical gardens), marine sediments (South China Sea, Arctic Ocean), aquaculture waters (shrimp farms), the intestinal tract of fish, and condensed milk.

As a plant growth-promoting rhizobacteria (PGPR), it colonizes roots, solubilizes nutrients, and improves soil microbiota, reducing erosion and contamination by pathogens.

In stressful environments (salinity, heavy metals), it acts as a bioremediator, degrading hydrocarbons and oxidizing manganese (up to 82% removal).

Its presence in space cleanrooms highlights its adaptability to low humidity and radiation, but in agriculture, it contributes to sustainability by replacing chemicals, minimizing impacts on soil biodiversity.

Etiological aspects

It is not pathogenic to plants or humans (classified as safe, GRAS-like), but it acts etiologically in the control of phytopathological diseases.

It inhibits the etiology of fungi and bacteria through antagonism, preventing root and leaf infections.

Studies have shown that strains like B21 and Y246 reduce the incidence of root rot in tomatoes and asparagus by inducing ISR (inhibition of root rot) and competing for space/nutrients.

There are no reports of disease causality; on the contrary, it mitigates etiology through abiotic stresses (salt, metals), reducing susceptibility to opportunistic pathogens.

Uses in agriculture

Biocontrol of phytopathogens: effective against fungi (Botrytis, Fusarium, Phytophthora) and bacteria, with endophytic strains (e.g., B21) inhibiting 70–100% of in vitro growth; applied to tomatoes, asparagus, and cotton to reduce pests such as larvae of spodoptera.

Promoting plant growth: Increases biomass (roots/leaves) by 20-50% via hormones and ACCD; formulations with RGM 2450 reduce fertilizers by 34% in tomatoes without loss of productivity.

Biofertilizer and biostimulant: It solubilizes phosphates, indirectly fixes nitrogen; it tolerates saline soils, improving yields in deserts or contaminated areas.

Bioremediation: It degrades plastics (PLA) and pollutants in agricultural soils, with strains such as ZY16 producing biosurfactants for hydrocarbons.

Commercial formulations: integrated into mixtures for foliar spraying or seed treatment.