Fruits and vegetables are the core components of daily diet, rich in vitamins, dietary fiber and organic acids, and are an important source for the human body to obtain these nutrients. However, due to the limitations of preservation technology and transportation storage conditions, the post-harvest storage and preservation period of fruits and vegetables is restricted. On one hand, the loss rate is high, which seriously affects the income of farmers; on the other hand, post-harvest fruits and vegetables are highly susceptible to pathogen infection, posing a threat to human health. Therefore, effectively extending the storage and preservation period of fruits and vegetables after harvest, reducing spoilage, is of great significance for improving economic benefits and ensuring food safety. 

Currently, post-harvest disease control of fruits and vegetables often employs both physical and chemical preservation methods. Among them, chemical fungicides are widely used. However, some targeted fungicides not only exacerbate the drug resistance of pathogenic bacteria but also pose potential hazards to human health and the environment. As a result, their large-scale application is strictly restricted. 

The microorganisms of the Bacillus genus are Gram-positive bacteria. They can produce metabolites such as antimicrobial peptides and organic acids, and have extensive antibacterial activity against bacteria and fungi. They are valuable resources for new natural antibacterial drugs. In addition, Bacillus can produce endospores. These spores have good resistance to high temperatures, drought and other harsh environments, and possess excellent processing properties. Therefore, they have become the preferred choice for the development of fruit and vegetable biological antibacterial agents. 

Post-harvest preservation of fruits and vegetables involves complex interactions among the quality of the fruits and vegetables, environmental factors, and pathogenic bacteria. The mechanism of Bacillus spores' role in post-harvest preservation of fruits and vegetables mainly includes two aspects: inhibiting and killing pathogenic bacteria and inducing the systemic resistance of the fruits and vegetables themselves. 

Survival space and nutritional competition between Bacillus bacteria and pathogenic bacteria 

Both antagonistic bacteria and pathogenic bacteria require oxygen in the environment and essential elements such as carbon, nitrogen, iron, and phosphorus for their growth and development to sustain their life activities. The contact between cells and their competition for space and nutrients are important mechanisms of biological control by spore-forming bacteria. There is competition for nutrients and space among microorganisms with the same physiological requirements. Especially in ecological niches with limited resources, antagonistic bacteria can more quickly absorb nutrients and prevent the germination and growth of pathogenic bacteria spores. 

Studies have observed the interaction between Bacillus subtilis B4 and pathogenic bacteria using scanning electron microscopy. It was found that this strain can colonize on post-harvest peach fruits and occupy the survival sites. Another study used the plate confrontation method to isolate three biocontrol bacteria from the rhizosphere soil of guava. By changing the inoculation time of the antagonistic spore bacteria and the pathogenic bacteria, it was discovered that the antagonistic bacteria could occupy the favorable space earlier, and the infection diameter of the pathogenic bacteria decreased, resulting in a better control effect on the soft rot disease of guava. 

The competition for nutrients among microorganisms plays a direct role in preventing fruit and vegetable diseases caused by pathogenic microorganisms. Ferritin is an important discovery in the study of nutrient competition. Microorganisms that produce iron carriers can rapidly chelate and absorb iron elements in the environment, inhibiting the absorption of iron by pathogenic bacteria. Microorganisms such as Bacillus subtilis, Bacillus amyloliquefaciens, and Thai Bacillus spores can produce a large amount of ferritin. However, their antibacterial effects are largely regulated by the content of iron elements in the environment, and there is usually a negative correlation between them. 

Spatial competition and nutrient competition often occur simultaneously. Some studies have conducted experiments by inoculating Bacillus subtilis HT-6 and potato pathogenic oomycete on the surface of a culture medium. The antagonistic bacterium HT-6 rapidly grew and spread on the surface of the medium, while the pathogenic bacteria failed to form normal large colonies. Moreover, Bacillus subtilis HT-6 can produce ferric iron, and its utilization rates of glucose and nitrate nitrogen are higher than those of potato pathogenic oomycete, proving that both spatial competition and nutrient competition exist simultaneously. 

Bacillus inhibits the growth of pathogenic bacteria. 

Bacillus spores can interfere or block the normal growth of pathogenic bacteria by acting on the cell wall, cell membrane, signal transduction pathways, and energy synthesis metabolism of the pathogenic bacteria. The cell wall of pathogenic fungi plays a protective role in maintaining cell morphology and normal metabolism. Bacillus spores can adhere to the hyphae of the pathogenic bacteria and produce lytic substances, such as chitinase, β-1,3-glucanase, and protease, which are cell wall-degrading enzymes, causing the hyphae to break, disintegrate, and the cytoplasm to be degraded, and even dissolving the spore cell wall, resulting in phenomena such as cell wall perforation and deformation, thereby preventing their germination and formation of normal mycelial bodies. 

The cytoplasmic membrane is involved in maintaining multiple key biological processes such as substance transport, information transmission, energy metabolism, and cell division. It is also an important target for bactericides. Metabolites produced by Bacillus species, such as bacteriocins, lipopeptides, and volatile antibacterial components, can disrupt the normal synthesis and structure of the cell membrane, damage the integrity of the pathogen's cell membrane, cause holes to form on the cell membrane, and accelerate cell lysis and death. 

Research has shown that antibacterial lipopeptides can even penetrate damaged cell membranes and act inside the cells. The antibacterial lipopeptide Fengycin secreted by Bacillus subtilis FZB42 reduces the mitochondrial membrane potential, induces the release of reactive oxygen species, disrupts the expression of DNA repair-related proteins, and even causes partial DNA fragmentation or degradation, thereby affecting the normal life activities of pathogenic bacteria. 

Bacillus-induced resistance effect 

The process of inducing resistance by Bacillus bacteria usually involves two aspects: structural defense and biochemical defense. In the structural defense aspect, under the induction of Bacillus bacteria or its metabolites, fruits and vegetables enhance their cell wall resistance by accumulating lignin, antibiotics, and synthesizing lysozymes, thereby activating their own disease resistance to resist pathogenic bacteria. For example, lignin, by depositing on the cell wall, affects the formation of lignification in plant tissues, thereby restricting the invasion of pathogenic bacteria. 

In the biochemical defense aspect, it is more complex and diverse. On one hand, fruits and vegetables will activate the synthesis of related enzymes, such as chitinase and β-1,3-glucanase, which can directly attack and degrade the cell walls of pathogenic bacteria. On the other hand, it can promote the accumulation of antibacterial substances like phenols and flavonoids. Research has confirmed that when Beles spore bacteria are inoculated on the surface of eggplants, it not only induces the upregulation of gene expression related to secondary metabolites (such as lignin, flavonoids, etc.) for resistance, but also increases the accumulation of these metabolites in eggplants, enhancing the resistance of eggplants to soft rot disease. 

A large amount of evidence indicates that the initiation and coordination of the above-mentioned defense responses rely on a complex signaling network within the plant. Bacillus species and their metabolites mainly activate the jasmonic acid and ethylene signaling pathways, thereby inducing systemic resistance. For example, when Arabidopsis is infected by the pathogenic strain of tomato gray mold, the inducing substances produced by the spore-forming bacterium SQR9 activate the jasmonic acid, salicylic acid and ethylene signaling pathways within the plant. 

Meanwhile, the volatile substances produced by Bacillus subtilis CF-3 can directly induce the down-regulation of the key pathogenic genes of the pathogenic bacteria. The knockout of this gene confirmed its significant role in weakening the pathogenicity of the bacteria. In summary, inducing resistance is essentially a signal pathway-mediated systemic defense. It achieves this through multiple defense responses such as integrating physical barrier defense, activation of defense-related proteins, and accumulation of antibacterial substances, providing effective disease resistance for harvested fruits and vegetables. 

In actual biological control applications, the mechanisms described above do not operate independently but form a closely complementary defense network to resist the invasion of pathogenic bacteria. The excellent preservation effect of Bacillus spores is also attributed to the synergy of these multiple mechanisms. 

This cooperative process usually begins with competitive action. Bacillus species successfully occupy the living environment on the surface of fruits and vegetables through rapid colonization and nutrient exploitation, laying the foundation for subsequent actions. Subsequently, antagonistic action is initiated, and the antibacterial substances such as lipopeptides and bacteriocins secreted by them can directly attack and weaken the vitality of pathogenic bacteria. At the same time, some volatile substances released by certain Bacillus species can induce the fruit and vegetable to activate its own systemic resistance mechanism, thereby enhancing its disease resistance and stress tolerance. 

Studies have shown that Bacillus belaisi and Bacillus sylviarum have highly effective control effects against strawberry botrytis and tomato gray mold respectively, confirming that the combined use of multiple mechanisms is the core for the effectiveness of Bacillus bacteria in different fruit and vegetable systems. 

Reference materials: 

[1] Tian Pingping, Mi Yuanyuan, Xu Jia, et al. Research progress on Bacillus for controlling post-harvest infectious diseases of fruits and vegetables and its mechanism of action [J]. Food Industry Science and Technology, 2025, 46(23): 440-447. 

[2] Yun Jing, Zhang Chunjie, Jiang Aili. Research Progress on the Antibacterial Mechanism of Bacillus and Its Application in Post-harvest Preservation of Fruits and Vegetables [J/OL]. Food and Fermentation Industry, 1-11 [2026-01-09]. 

Author Profile: 

Xiao Nisan, a food technology professional, holds a master's degree in food science. Currently, he works at a large domestic pharmaceutical research company, specializing in the development and research of nutritional foods.