1 Introduction

Bacillus tequilensis is widely found in nature, including mineral soils, animal intestines, and plant rhizospheres. The first strain of B. tequilensis was discovered in a tomb (Sun, 2020). Subsequent phenotypic and phylogenetic analyses identified it as a member of the Bacillus genus. Numerous studies have shown that B. tequilensis exhibits strong antibacterial activity, making it a promising biocontrol strain. To date, research on B. tequilensis in China is limited, with most studies focusing on its applications in biological control, indicating substantial potential for further development. Research has shown that B. tequilensis can control pathogenic fungi such as Ceratocystis fimbriata (Li et al., 2022), Colletotrichum camelliae (Zhou et al., 2023), and Verticillium dahliae (Shen et al., 2018), as well as pathogenic bacteria like Elizabethkingia miricola, Stenotrophomonas maltophilia, and Aeromonas hydrophila (Zhu et al., 2024). Additionally, it has properties for algicidal activity (Shao, 2021), pulp bleaching (Angural et al., 2020), and mitigating heavy metal pollution (Li, 2018b), demonstrating broad application prospects. Therefore, B. tequilensis has the potential to become an eco-friendly biological agent.

2 Origin and Characteristics of Bacillus tequilensis

An endophytic antagonistic strain of B. tequilensis X-16 was isolated from the "Meizao" sweet cherry at the Tianping Lake Base of the Shandong Institute of Pomology. Its fermentation broth and supernatant can effectively inhibit Monilinia fructicola, the causal agent of brown rot in stone fruits, effectively addressing the rot problem caused by this pathogen in "Meizao" sweet cherries (Xi et al., 2020). The strain B. tequilensis wm031, isolated from tomato plants, exhibits significant antagonistic activity against pathogens such as Fusarium oxysporum (causing tomato wilt), Gibberella fujikuroi (causing bakanae disease in rice), and Fusarium oxysporum f. sp. niveum (causing watermelon wilt). Using rifampicin marker technology, wm031 was found to have strong colonization capabilities in tomato, watermelon, and rice crops (Zhang et al., 2017b). A strain RA1402 was isolated from rhizosphere soil at a sorghum aphid outbreak site in Yibin, showing strong anti-aphid activity (Zhang et al., 2017a). The strain B. tequilensis 36, isolated from cycad rhizosphere soil, was applied in solid-state fermentation of tea, effectively enhancing tea flavor with a subtle fruity aroma, stabilizing tea quality, and imparting a unique taste (Li et al., 2018). Another strain, B. tequilensis CD36, also isolated from cycad rhizosphere soil, is a high-yield siderophore producer. It produces growth-promoting substances with phosphate-solubilizing and potassium-dissolving activities, indicating its potential for soil remediation (Li, 2018b). A strain B. tequilensis HS10, isolated from peanut rhizosphere soil, secretes indole-3-acetic acid (IAA). Pot experiments with peanuts showed that HS10 significantly increased IAA content in the soil, thus markedly promoting root growth and development (Zhang et al., 2016). The strain JN-3 69, collected from Huatian Village, Shiniujiang Town, Taojiang County, Hunan Province, China, produces volatile organic compounds (VOCs), crude protein extracts, and crude lipid extracts that inhibit Magnaporthe oryzae, the rice blast pathogen (Zhou et al., 2019). Additionally, strains B. tequilensis LSG3-6 and CC2FG2, isolated from animal intestines, exhibit acid and bile salt tolerance (Wu, 2020; Wei et al., 2022) (Table 1).

Table 1 The sources, functions and characteristics of B. tequilensis

3 Applications in the Field of Biological Control

Currently, there has been substantial research on B. tequilensis in the field of biological control. As a broad-spectrum antagonistic bacterium, B. tequilensis exhibits wide-ranging resistance against various pathogens.

Studies have shown that B. tequilensis can inhibit pathogenic fungi such as Aspergillus niger, Mucor spp. (Li et al., 2016), Phytophthora nicotianae (causing black shank disease in tobacco) (Feng et al., 2011), Monilinia fructicola (causing brown rot in peaches) (Yuan et al., 2018), and Ceratocystis fimbriata (causing black rot in sweet potato) (Li et al., 2022). Researchers have leveraged the antifungal properties of B. tequilensis in numerous plant disease resistance studies, revealing that it can significantly inhibit brown rot in sweet cherries (Xi et al., 2020), effectively control mulberry sclerotinia disease (Xie et al., 2015) and Colletotrichum camelliae (causing anthracnose in tea plants) (Zhou et al., 2023), and partially suppress soybean anthracnose (Gholami et al., 2013). B. tequilensis has been found to control Verticillium dahliae (causing potato wilt) (Shen et al., 2018), Saprolegnia spp. (causing water mold disease) (Wang, 2020), and Rhizopus spp. (causing blueberry rot) (Huang et al., 2017). It also reduces the severity of avocado anthracnose (Wang et al., 2019) and decreases the incidence of banana leaf spot disease (Cuellar-Gaviria et al., 2021). In an experiment conducted by Zhang et al. (2017), the control efficacy of B. tequilensis against watermelon wilt was found to be 74.6%. However, when B. tequilensis was adsorbed onto rice husk biochar, the control efficacy increased to 83.1% (Zhang et al., 2019), outperforming the direct application of the bacterial solution. This comparative data suggests that the use of biochar as a carrier can enhance the effectiveness of B. tequilensis in managing soil-borne diseases in crops. In another study by Gao Yuan et al. (2022), plate confrontation experiments revealed that B. tequilensis, when mixed in specific ratios with Bacillus velezensis and two other Bacillus species, significantly inhibited Alternaria spp. and Botrytis cinerea, with inhibition rates exceeding 80%, thereby enhancing the biological control effect. Field trials indicated that the composite Bacillus mixture achieved control effects against Alternaria and Botrytis comparable to current chemical treatments, but with greater environmental friendliness, aligning well with green pest management strategies (Gao et al., 2022). Research by Liu Xiaodan et al. (2018) found that mixing B. tequilensis with Bacillus pumilus, Bacillus subtilis, and Paenibacillus polymyxa in certain ratios and using bone meal as a carrier not only increased IAA content but also enhanced the accumulation of available phosphorus and nitrogen, resulting in increased corn yield (Liu et al., 2018). Thus, to enhance biocontrol efficacy, B. tequilensis can be combined with carriers, mixed with other Bacillus species, or integrated with both carriers and other Bacillus strains. These three strategies offer valuable reference points for the future development of bio-fertilizers and microbial agents.

In addition to its antifungal properties, B. tequilensis also exhibits antibacterial activity. Studies have found that B. tequilensis shows inhibitory effects against various pathogenic bacteria of the dark-spotted frog, including Elizabethkingia miricola, Stenotrophomonas maltophilia, and Aeromonas hydrophila (Zhu et al., 2024). It can also produce cellulase and protease, assisting Blattella germanica (German cockroach) in digesting proteins, starch, and cellulose, while also providing antagonistic protection against Beauveria bassiana infection (Huang, 2019). Singh and Sharma (2020) demonstrated experimentally that B. tequilensis kills bacteria by producing biosurfactants, which act similarly to disinfectants. Zhang Haiying et al. (2017a) isolated a strain of B. tequilensis from the rhizosphere soil of sorghum that exhibited resistance against sorghum aphids. Li Jing (2018a) discovered that adding B. tequilensis to the aquaculture water of sea cucumber (Apostichopus japonicus) significantly enhanced the growth of sea cucumber and increased the enzymatic activities of amylase, trypsin, and superoxide dismutase (SOD) in the gut.

Therefore, B. tequilensis holds great promise for applications in agricultural biological control.

4 Applications in Other Fields

B. tequilensis is not only gaining attention in the agricultural sector but also shows significant application potential in the industrial, environmental, and food industries, warranting further research and exploration.

In the paper industry, B. tequilensis can be used for pulp bleaching (Angural et al., 2020). In the petroleum industry, B. tequilensis has the potential to generate gas, emulsify, and enhance oil recovery under anaerobic conditions, demonstrating good oil reservoir adaptability and potential for oil extraction (Lin et al., 2019).

In the field of food fermentation, there have been bold explorations using B. tequilensis to ferment rapeseed meal. During the fermentation process, proteases secreted by B. tequilensis break down rapeseed protein into small peptides and proteins, increasing the amino acid content, which also exhibits antioxidant activity (Zhong et al., 2022).

In the environmental sector, siderophores secreted by B. tequilensis can mitigate the stress and toxicity of Ni²⁺ and Pb²⁺ on plants, enhancing the efficiency of phytoremediation of heavy metal pollution (Li, 2018b). Research by Shao Xueping (2021) indicated that the algicidal compounds (surfactin-like substances) produced by B. tequilensis D8 exhibit strong algicidal activity against four types of algae: Pseudo-nitzschia delicatissima, Skeletonema costatum, Heterosigma akashiwo, and Prorocentrum donghaiense. The algicidal effects are relatively stable, providing experimental support for red tide control.

5 Main Active Compounds

During its growth and reproduction, B. tequilensis produces numerous secondary metabolites, primarily including lipopeptides (biosurfactants) (Singh and Sharma, 2020) with antagonistic activity against pathogens, antibacterial proteins (such as cellulase, protease, and gelatinase) (Guan, 2018), and polyketides. Additionally, it produces growth-promoting substances for plants, such as indole-3-acetic acid (IAA), ACC deaminase, and siderophores (Guan, 2018). It also synthesizes amino acids, organic acids, and thiamine, which regulate cell growth and metabolism.

Importantly, the bioactive metabolites of B. tequilensis maintain high activity under conditions of high temperature, strong acidity, neutral pH, mild alkalinity, and UV irradiation (Jiang et al., 2023). In contrast, other biocontrol strains often exhibit low bioactivity under these conditions, limiting their effectiveness in biological control. B. tequilensis overcomes these limitations, making it a superior biocontrol strain and laying a solid foundation for its future applications across various fields.

6 Summary and Prospect

Some studies have shown that B. tequilensis can produce highly effective bioactive compounds; however, the types of these active compounds and their mechanisms of action remain unclear and require further investigation. Many reports on the biological control potential of B. tequilensis are based primarily on results from in vitro plate confrontation experiments, while field trials are relatively scarce. It is well known that the biocontrol efficacy observed in laboratory assays can differ significantly from that seen in field applications. Therefore, when promising results are obtained indoors, it is crucial to conduct large-scale field trials under various conditions to validate the actual biocontrol effectiveness of the target strain and determine its practical application value.

Moreover, the antimicrobial substances secreted by B. tequilensis are stable and effective, playing an important role in the sustainable development of both agriculture and industry. It is anticipated that in the future, B. tequilensis will find broader applications across multiple fields.

Funding

This study was funded by the project of Guangxi Minzu University's Autonomous Region-level College Student Innovation and Entrepreneurship Training Program Fund (S202310608308).

Acknowledgments

Thanks to the reviewers for their valuable feedback, which has helped improve the the manuscript.

Conflict of Interest Disclosure

The authors affirm that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest.

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