Bacillus Thuringiensis Berliner: A Key Biological Agent for Sustainable Agriculture

The increasing population of the world means further demand for agricultural production while imposes decreased access to irrigation water and agricultural lands. In spite of the hazardous impact of the chemical pesticides announced at least since the publication of the noble-prize winning Silent Spring [1], unfortunately the current rate of water and soil pollution is enough high to testify for the undeniable mismanagement of these invaluable environmental resources. The situation has got more aggravated due to other pollutants from industrial and civil activities. Air pollution due to the increased application of fossil fuels and irresponsible annihilation/use of forests is believed to be the main reason of global warmth. So, finding eco-friendly agrobiologicals replacements for current agrochemicals may be helpful in the reduction of farmers’ reliance on agrochemical products. Among the most appropriate agrobiologicals are those based on the bacterium Bacillus thuringiensis Berliner, accounting for more than 90% of the global biopesticide employment [2].

The bacterium, about 0.5-1.0 × 2-5μm in size [3], is a cultivable aerobic or anaerobic facultative [4] gram-positive, thick-walled peritrichous species able to chemotactically trace and swim toward plant root exudates or target (micro) organisms [5]. There are strains of the bacterium able to promote plant growth and development and increase its yield [6]. Its antagonistic activity against plant pathogenic fungi including the mycotoxigenic Fusarium oxysporum is well documented [7]. The bacterium produces and secrets a range of antibacterial (such as bacteriocins) and antifungal metabolites (such as Zwittermicin, fengycin, and hydrogen cyanide) [8,9]. However, the bacterium is more famous because of its capacity for the production of insecticidal crystal proteins and metabolites. Based on flagellar H antigens, host specificity and the presence of plasmids, the species is divided to more than 100 sub-species and varieties divided into 70 serotypes [3]. Also, there are various types of Cry proteins each effective against specific group of insect pests [5]. Some Cry proteins are nematicidal [5]. Other insecticidal proteins produced by B. thuringiensis are vegetative Insecticidal Proteins (VIPs), and cytotoxic proteins (Cyt proteins) [10]. Furthermore, B. thuringiensis produces several classes of other toxins such as alpha-exotoxins, beta-exotoxins, hemolysins, enterotoxins as well as enzymes such as phospholipases, chitinase [11] as well as proteases [12]. The bacterium incites all three hormonal signaling pathways involved in plant systemic resistance to a broad range of plant pathogens and pests [13]. All these characteristics make this species an ideal candidate for integrated plant disease and pest management programs. The endospores are known as the most persistent form of life [14]. It is expectable, that the bacteria will produce endospores receiving the signals of plant senescence at the end of growing season. This is important as more than 90% of world agricultural lands may be classified as conducive soils [15] and the annual increase of the persistent bacterial propagules can lead to a shift in the soil biology from conduciveness to suppression.

The application of a bacterial strain of a sum of abovementioned bioactivities is superior to the chemical treatments that even if they are not pollutant, only affect either plant pathogens or pests. Additionally, the use of the bacterium is preferred to the pre-treatment of plants with plant resistance inducing chemicals (such as salicylic acid, jasmonic acid, etc.) because such chemical treatments applied prior to the beginning of plant diseases or pest contamination can lead to reduced crop yields due to consumed material and energy for the activation of unnecessary defense pathways in the absence of the disease or pest [16]. The suitable B. thuringiensis can increase plant growth, development, and yield in the absence of the harmful (micro) organisms [6]. Considering the widespread use of cry genes in the biotechnological generation of genetically transformed crops [17], the pretreatment of plants with an appropriate stain(s) of B. thuringiensis does not need economically expensive and technically difficult procedures of genetic engineering, genetic transformation, and tissue culture followed by time-consuming and labor-requiring transformed plant propagation. From the medicinal point of view, B. thuringiensis is a species closely relative to Bacillus spp. (B. cereus, and B. anthracis) pathogenic in human [18]. This means that B. thuringiensis may compete with pathogenic Bacillus spp. And help into hygiene and health in rural environments. However, the carriage of Cry toxin plasmids substantially reduces B. thuringiensis competitive potential in soil [19]. The bacterium can be easily formulated thanks to its constitutive ability to produce persistent endospores [20]. The endospore-based formulations are of prolong shelf-life [21]. The resistant endospores can guarantee the persistence of the soil biology improvement despite of global warmth and harsh changes in the local climate. B. thuringiensis and autochthonous arbuscular mycorrhizal fungi can be applied to improve the physiological traits as well as performance of agronomical crops under drought conditions [22].

Bacillus Thuringiensis can be useful in the ecofriendly development of global agriculture and improve the ecology and economy of the developing as well as developed countries affected with agrochemicals and the harmful impact of global warmth.

1. Carson R (1962) Silent Spring-1, The New Yorker, New York, USA.
2. Lambert B, Peferoen M (1992) Insecticidal promise of Bacillus thuringiensis: Facts and mysteries about a successful biopesticide. Bioscience 42(2): 112-122.
3. Khachatourians GG (2019) Insecticides, microbial. Reference Module in Life Sciences, pp. 95-109.
4. Schünemann R, Knaak N, Fiuza LM (2014) Mode of action and specificity of Bacillus thuringiensis toxins in the control of caterpillars and stink bugs in soybean culture. ISRN Microbiol 2014: 13567.
5. Schnepf E, Cickmore N, Van Rie J, Lereclus D, Baum J, et al. (1998) Bacillus thuringiensis and its pesticidal crystal proteins. Microbiol Mol Biol Rev 62(3): 775-806.
6. Azizoglu U (2019) Bacillus thuringiensis as a biofertilizer and biostimulator: A mini-review of the little known plant growth-promoting properties of Bt. Curr Microbiol 76(11): 1379-1385.
7. Al Banna L, Horani HK, Sadder M, Zahra SA (2016) Efficacy of some local Bacillus thuringiensis isolates against soil borne fungal pathogens. African Journal of Agricultural Research 11(19): 1750-1754.
8. Raddadi N, Cherif A, Ouzari H, Marzorati M, Brusetti L, et al. (2007) Bacillus thuringiensis beyond insect biocontrol: Plant growth promotion and biosafety of polyvalent strains. Annals of Microbiology 57(4): 481-494.
9. Lecadet MM, Frachon E, Dumanoir VC, Ripouteau H, Hamon S, et al. (1999) Updating the H-antigen classification of Bacillus thuringiensis. J Appl Microbiol 86(4): 660-672.
10. Bravo A, Martínez DeCastro DL, Sánchez J, Cantón PE, Mendoza G, et al. (2015) 30-Mechanism of action of Bacillus thuringiensis insecticidal toxins and their use in the control of insect pests. In: Alouf J, Ladant D, Popoff MR (Eds.), The Comprehensive Sourcebook of Bacterial Protein Toxins (4^th edn), Academic Press, Massachusetts, USA, pp. 858-873.
11. Hansen BM, Salamitou S (2000) Virulence of Bacillus thuringiensis. In: Charles JF, Delecluse A, Nielsen-Le RC (Eds.), Entomopathogenic Bacteria: From Laboratory to Field Application, Kluwer Academic Publishers, Europe, pp. 41-44.
12. Lövgren A, Zhang MY, Engström A, Dalhammar G, Landén R (1990) Molecular characterization of immune inhibitor A, a secreted virulence protease from Bacillus thuringiensis. Mol Microbiol 4(12): 2137-2146.
13. Dezhabad M, Taheri H, Pakdaman BS (2018) Bacillus thuringiensis-mediated priming induces jasmonate/ethylene and salicylic acid-dependent defense pathways genes in tomato plants. Journal of Plant Molecular Breeding 6(2): 61-69.
14. Nicholson WL, Munakata N, Horneck G, Melosh HJ, Setlow P (2000) Resistance of Bacillus endospores to extreme terrestrial and extraterrestrial environments. Microbiology and Molecular Biology Reviews 64(3): 548-572.
15. Higa T, Parr JF (1994) Beneficial and effective microorganisms for a sustainable agriculture and environment. International Nature Farming Research Center, pp. 1-16.
16. Denancé N, Vallet AS, Goffner D, Molina A (2013) Disease resistance or growth: The role of plant hormones in balancing immune responses and fitness costs. Frontiers in Plant Science 4: 155.
17. Rahman M, Zaman M, Shaheen T, Irem S, Zafar Y (2015) Safe use of cry genes in genetically modified crops. Environmental Chemistry Letters 13: 239-249.
18. Drobniewski FA (1993) Bacillus cereus and related species. Clin Microbiol Rev 6(4): 324-338.
19. Yara K, Kunimi Y, Iwahana H (1997) Comparative studies of growth characteristic and competitive ability in Bacillus thuringiensis and Bacillus cereus in soil. Applied Entomology and Zoology 32(4): 625-634.
20. Addison JA (1993) Persistence and non-target effects of Bacillus thuringiensis in soil: A review. Canadian Journal of Forest Research 23(11): 2329-2342.
21. Chattopadhyay L, Majumdar B, Mazumdar SP, Saha AR, Saha R, et al. (2019) Use of bacterial endospore with longer shelf-life in improved retting of jute. Journal of Environmental Biology 40(2): 245-251.
22. Armada E, Azcon R, Lopez-Castillo OM, Calvo-Polanco M, Ruiz-Lozano JM (2015) Autochthonous arbuscular mycorrhizal fungi and Bacillus thuringiensis from degraded Mediterranean area can be used to improve physiological traits and performance of a plant of agronomic interest under drought conditions. Plant Physiol Biochem 90: 64-74.