Bacillus subtilis
The most widely used bacterial biocontrol agent in agriculture, working by several mechanisms at once.
What is bacillus subtilis?
Bacillus subtilis is a Gram-positive, spore-forming soil bacterium — one of the best-characterised organisms in biology and a workhorse of industrial fermentation. Its spore-forming ability is what makes it commercially practical: spores survive formulation, storage and application in a way that vegetative cells do not.
How does bacillus subtilis work?
Antibiosis: it produces a range of antimicrobial lipopeptides, including surfactins, iturins and fengycins, which disrupt fungal membranes. Iturins and fengycins in particular have direct antifungal activity.
Competition: it colonises root surfaces rapidly, occupying space and consuming root exudates that pathogens would otherwise use.
Induced systemic resistance: colonisation primes the plant's own defence pathways, so the plant responds faster to subsequent attack. This is a genuinely different mode from direct antagonism and part of why effects can appear at sites the bacterium has not colonised.
Plant growth promotion: phosphate solubilisation and production of plant hormones, contributing to root development independently of disease suppression.
Having several mechanisms operating together is the main argument for durability against resistance, and a real point of difference from single-site synthetic fungicides.
What does bacillus subtilis not do?
It is preventive and establishment-dependent, not curative — it needs to colonise before or as pressure arrives, and applying it to an established epidemic will disappoint. Colonisation depends on soil biology, moisture, temperature and organic matter, so performance varies more by site than a chemical would. It is not a fungicide substitute under high disease pressure. And it competes with the existing soil microbial community, which in a biologically active soil may already occupy the niche.
Is bacillus subtilis safe?
Very low risk. Non-pathogenic to humans, animals and plants, no residue concerns, and widely accepted in organic programmes. Inhalation of concentrated spore powder should be avoided during handling, as with any microbial product.
Where does bacillus subtilis appear in the range?
Bacillus subtilis is one of eleven strains in Charge BioBoost, alongside three other Bacillus species, five mycorrhizal species and two Trichoderma species, in a humic, fulvic, amino-acid and kelp base.
References
- Bacillus lipopeptides: versatile weapons for plant disease biocontrol
- Surfactin and fengycin lipopeptides of Bacillus subtilis as elicitors of induced systemic resistance in plants
- Biocontrol of Bacillus subtilis against infection of Arabidopsis roots by Pseudomonas syringae is facilitated by biofilm formation and surfactin production