Plant protection and growth stimulation by microorganisms: biotechnological applications of Bacilli in agriculture

Aims: A Bacillus amyloliquefaciens strain, surviving epiphytically on the surface of fruit, was isolated while searching for naturally occurring biological control agents This bacterial strain was characterized for its antifungal activity against seven selected fungal postharvest pathogens of citrus Methods and Results: To understand the antifungal activity, seven postharvest fungal pathogens were screened for growth inhibition by B amyloliquefaciens strain Assays using B amyloliquefaciens lipopeptide extracts showed a strong inhibitive activity The inhibitory effect was observed in abnormal conidial germination and germ tube development when conidia were treated with different lipopeptide extract concentrations Further analysis using PCR and chromatography confirmed the presence of fengycin, iturin and surfactine, of which iturin A showed the strongest and most common inhibitory effect The results are supported by site-directed mutagenesis analysis, targeted to suppress the biosynthesis of iturin A production Fruit trials confirmed disease development inhibition when the antagonist was applied 1 day prior to or 1 day after fungal application Conclusions: We conclude that the iturin family of lipopeptides are vital in the antagonism of B amyloliquefaciens against the seven citrus postharvest pathogenic fungi tested Significance and Impact of the Study: We elucidated the principal mechanism used by B amyloliquefaciens PPCB004 to suppress postharvest disease development on stored fruits

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2672.2009.04438.x

Iturin A is the principal inhibitor in the biocontrol activity of Bacillus amyloliquefaciens PPCB004 against postharvest fungal pathogens

Endophytes are microorganisms that live within host plants for at least part of their life and do not cause apparent symptoms of diseases. In general, beneficial endophytes promote host plant growth, increase plant nutrient uptake, inhibit plant pathogen growth, reduce disease severity, and enhance tolerance to environmental stresses. As sustainable and renewable agricultural production (including current biofuel and bioenergy crops) increases in prominence, endophytic microorganisms will play important roles and offer environmentally-friendly methods to increase productivity while reducing chemical inputs. This review discusses various aspects of beneficial fungal and bacterial endophyte interactions with plants, including the physiological and molecular mechanisms by which they benefit plant performance. We also discuss the potential for genetic modification of endophytes with useful genes, which could be used to impart additional traits following inoculation with the genetically engineered endophytes. Finally, we review US-issued patents over the past decade which relate to the use of fungal and bacterial endophytes for plant growth and stress tolerance improvement.

The use of beneficial microbial endophytes for plant biomass and stress tolerance improvement.

Plant diseases cause considerable losses in crop production and storage. Nowadays, growers still rely heavily on chemical pesticides to prevent, or control these diseases. However, the high effectiveness and ease of utilization of these chemicals can result in environmental contamination and the presence of pesticide residues on food, in addition to social and economic problems. Consequently, there is an increasing demand from consumers and officials to reduce the use of chemical pesticides. In this context, biological control through the use of natural antagonistic microorganisms has emerged as a promising alternative. Indeed, these biopesticides present many advantages in term of sustainability, mode of action and toxicity compared to chemical pesticides. Here, we focus in details on the versatile utilization of Bacillus based products as biopesticides. More precisely, a special emphasis is given to the three main specific mechanisms involved in biocontrol of plant diseases by this bacterial genus: competition for ecological niche/substrate in the rhizosphere, production of inhibitory chemicals and induction of so-called systemic resistance in host plants. Beside this, strategies for enhancing the efficacy of Bacillus-based biopesticides are also discussed.

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Bacillus-based biological control of plant diseases

The postharvest diseases of citrus fruit cause considerable losses during storage and transportation. These diseases are managed principally by the application of synthetic fungicides. However, the increasing concern for health hazards and environmental pollution due to chemical use has required the development of alternative strategies for the control of postharvest citrus diseases. Management of postharvest diseases using microbial antagonists, natural plant-derived products and Generally Recognized As Safe compounds has been demonstrated to be most suitable to replace the synthetic fungicides, which are either being banned or recommended for limited use. However, application of these alternatives by themselves may not always provide a commercially acceptable level of control of postharvest citrus diseases comparable to that obtained with synthetic fungicides. To provide more effective disease control, a multifaceted approach based on the combination of different postharvest treatments has been adopted. Actually, despite the distinctive features of these alternative methods, several reasons hinder the commercial use of such treatments. Consequently, research should emphasize the development of appropriate tools to effectively implement these alternative methods to commercial citrus production.

Alternative methods for the control of postharvest citrus diseases

Biological control of take-all in wheat by endophytic Bacillus subtilis E1R-j and potential mode of action.

In this study, the biocontrol efficacies of 14 endophytic bacterial strains were tested against Blumeria graminis f. sp. tritici (Bgt) in pot experiments under greenhouse conditions. Bacillus subtilis strain E1R-j significantly reduced disease index and exhibited the best control (90.97%). When different formulations of E1R-j were sprayed 24 h before Bgt inoculation, fermentation liquid without bacterial cell and crude protein suspension displayed the similar effects; and they reduced disease index more than bacterial cell suspension (109 cfu mL−1) and fermentation liquid without protein. The control effects were not significantly different between 1011 and 109 cfu mL−1 of bacterial cell suspension but were higher than 107 cfu mL−1. Further observations showed that conidial germination and appressorial formation of Bgt were retarded by spraying E1R-j 24 h before Bgt inoculation. Compared with the water check, conidial germination and appressorial formation were decreased by 43.3% and 42.7%, respectively. In the treatment with E1R-j, the number of houstoria significantly reduced and the speed of mycelial extension was slowed down in the wheat leaves. Scanning electron microscopy observation revealed that E1R-j significantly suppressed the conidial germination and caused rupture and deformation of germ tubes. On the surface of wheat leaves, mycelia and conidiophores became shrinking.

/pdf/endophytic-bacillus-subtilis-strain-e1r-j-is-a-promising-3rzajpcf9p.pdf

Endophytic Bacillus subtilis Strain E1R-J Is a Promising Biocontrol Agent for Wheat Powdery Mildew

The invention discloses a Bacillus sp. E1R-j, which is preserved in China General Microbiological Culture Center of Microbial Culture Collection Management Committee on August 16th, 2007 with the preservation number of CGMCC No.2134; the invention further discloses a strain separating and identifying method, a thallus preparation method and a preparation method of an antimicrobial active substance, as well as applications of the E1R-j strain, the thallus and the antimicrobial active substance of the strain in controlling diseases including wheat take-all, Blumeria graminis and wheat yellow stripe rust as well as promoting seed germination and growth of wheat. The E1R-j strain is obtained from wheat root, has simple screening method, convenient operation, stable product quality, environmental protection and remarkable effects on controlling wheat take-all, Blumeria graminis and wheat yellow stripe rust, and does not have toxic side effect.

Yufei Gong

Papers

Biological control of take-all in wheat by endophytic Bacillus subtilis E1R-j and potential mode of action.

Endophytic Bacillus subtilis Strain E1R-J Is a Promising Biocontrol Agent for Wheat Powdery Mildew

Bacillus for preventing wheat diseases, as well as preparation and use thereof