Aphicidal Activity of Surfactants Produced by Bacillus atrophaeus L193

Bacillus amyloliquefaciens AK-12 Helps Rapeseed Establish a Protection against Brevicoryne brassicae

Aphids are a serious threat to rapeseed (Brassica napus L.) production, and cause unmanageable loss. Therefore, effective prevention and management strategies are urgently required to avoid losses. Bacillus amyloliquefaciens AK-12 isolated from a dead aphid with aphicidal activity was tagged with a green fluorescent protein through a natural transformation. The transformed strains were checked for stability and growth, and the best-performing strain was tested for its colonization inside and outside the rapeseed plant. The stability of AK-12-GFP reached more than 95%, and the growth curve was consistent with that of AK-12. After 30 days of treatment, the colonization of 1 × 106 CFU/g was recorded in rapeseed leaves. Interestingly, AK-12 reduced the aphid transmission rate compared with the control and improved the growth of the rapeseed seedlings. Meanwhile, the AK-12 strain also exhibited phosphorus, potassium-solubilizing, and nitrogen-fixing activity, and produced 2.61 µg/mL of IAA at 24 h. Regulation in the activity of four enzymes was detected after the AK-12 treatment. Phenylalanine ammonia lyase (PAL) was recorded at a maximum of 86.84 U/g after 36 h, and catalase (CAT) decreased after 48 h; however, peroxidase (POD) and polyphenol oxidase (PPO) reached the maximum within 12 h of AK-12 application. Additionally, important resistance genes related to these enzymes were upregulated, indicating the activation of a defense response in the rapeseed against aphids. In conclusion, defense enzymes and defense-related gene activation could improve the pest resistance in rapeseed, which has good application prospects for the future to be developed into biopesticide.

Plant protection from virus: a review of different approaches

This review analyzes methods for controlling plant viral infection. The high harmfulness of viral diseases and the peculiarities of viral pathogenesis impose special requirements regarding developing methods to prevent phytoviruses. The control of viral infection is complicated by the rapid evolution, variability of viruses, and the peculiarities of their pathogenesis. Viral infection in plants is a complex interdependent process. The creation of transgenic varieties has caused much hope in the fight against viral pathogens. The disadvantages of genetically engineered approaches include the fact that the resistance gained is often highly specific and short-lived, and there are bans in many countries on the use of transgenic varieties. Modern prevention methods, diagnosis, and recovery of planting material are at the forefront of the fight against viral infection. The main techniques used for the healing of virus-infected plants include the apical meristem method, which is combined with thermotherapy and chemotherapy. These methods represent a single biotechnological complex method of plant recovery from viruses in vitro culture. It widely uses this method for obtaining non-virus planting material for various crops. The disadvantages of the tissue culture-based method of health improvement include the possibility of self-clonal variations resulting from the long-term cultivation of plants under in vitro conditions. The possibilities of increasing plant resistance by stimulating their immune system have expanded, which results from the in-depth study of the molecular and genetic bases of plant resistance toward viruses and the investigation of the mechanisms of induction of protective reactions in the plant organism. The existing methods of phytovirus control are ambiguous and require additional research. Further study of the genetic, biochemical, and physiological features of viral pathogenesis and the development of a strategy to increase plant resistance to viruses will allow a new level of phytovirus infection control to be reached.

Acaricidal Activity and Field Efficacy Analysis of the Potential Biocontrol Agent Bacillus vallismortis NBIF-001 against Spider Mites

In recent years, spider mites have caused considerable economic losses to global agriculture. However, currently available management strategies are limited because of the rapid development of resistance. In this study, Bacillus vallismortis NBIF-001 was isolated and evaluated for its acaricidal activity. NBIF-001 exhibited a significant lethal effect on spider mites within 48 h. The median lethal concentration (LC₅₀) of the culture powders (3.2 × 10¹⁰ CFU/g) was 50.2 µg/mL for Tetranychus urticae (red form), 18.0 µg/mL for T. urticae (green form), and 15.7 µg/mL for Panonychus citri (McGregor). Cultivation optimisation experiments showed that when the number of spores increased, fermentation toxicity also increased. Moreover, field experiments demonstrated that NBIF-001 performed well in the biocontrol of P. citri, which showed a similar corrected field efficacy with the chemical control (67.1 ± 7.9% and 71.1 ± 6.4% after 14 days). Genomics analysis showed that NBIF-001 contains 231 factors and seven gene clusters of metabolites that may be involved in its acaricidal activity. Further bioassays of the fermentation supernatants showed that 50× dilution treatments killed 72.5 ± 5.4% of the mites in 48 h, which was similar with those of the broth. Bioassays of the supernatant proteins confirmed that various proteins exhibited acaricidal activity. Five candidate proteins were expressed and purified successfully. The bioassays showed that the small protein BVP8 exhibited significant acaricidal activity with an LC₅₀ of 12.4 μg/mL (T. urticae). Overall, these findings suggest that B. vallismortis NBIF-001 is a potential biocontrol agent for spider mite management.

Root-Associated Bacteria Are Biocontrol Agents for Multiple Plant Pests

Biological control is an important process for sustainable plant production, and this trait is found in many plant-associated microbes. This study reviews microbes that could be formulated into pesticides active against various microbial plant pathogens as well as damaging insects or nematodes. The focus is on the beneficial microbes that colonize the rhizosphere where, through various mechanisms, they promote healthy plant growth. Although these microbes have adapted to cohabit root tissues without causing disease, they are pathogenic to plant pathogens, including microbes, insects, and nematodes. The cocktail of metabolites released from the beneficial strains inhibits the growth of certain bacterial and fungal plant pathogens and participates in insect and nematode toxicity. There is a reinforcement of plant health through the systemic induction of defenses against pathogen attack and abiotic stress in the plant; metabolites in the beneficial microbial cocktail function in triggering the plant defenses. The review discusses a wide range of metabolites involved in plant protection through biocontrol in the rhizosphere. The focus is on the beneficial firmicutes and pseudomonads, because of the extensive studies with these isolates. The review evaluates how culture conditions can be optimized to provide formulations containing the preformed active metabolites for rapid control, with or without viable microbial cells as plant inocula, to boost plant productivity in field situations.

Lipopeptide Biosurfactants from Bacillus spp.: Types, Production, Biological Activities, and Applications in Food

Biosurfactants are a functionally and structurally heterogeneous group of biomolecules produced by multiple filamentous fungi, yeast, and bacteria, and characterized by their distinct surface and emulsifying ability. The genus Bacillus is well studied for biosurfactant production as it produces various types of lipopeptides, for example, lichenysins, bacillomycin, fengycins, and surfactins. Bacillus lipopeptides possess a broad spectrum of biological activities such as antimicrobial, antitumor, immunosuppressant, and antidiabetic, in addition to their use in skincare. Moreover, Bacillus lipopeptides are also involved in various food products to increase the antimicrobial, surfactant, and emulsification impact. From the previously published articles, it can be concluded that biosurfactants have strong potential to be used in food, healthcare, and agriculture. In this review article, we discuss the versatile functions of lipopeptide Bacillus species with particular emphasis on the biological activities and their applications in food.

Effects of surfactins, Bacillus lipopeptides, on the behavior of an aphid and host selection by its parasitoid

BACKGROUND

Lipopeptides extracted from the Bacillus genus are emerging biopesticides, especially in protecting crops against phytopathogens. Among the three main families of lipopeptides, surfactins have been identified as having insecticidal properties against several insect orders. However, the sublethal effects of these promising biopesticides on insect pests and their natural enemies remain largely unknown. The aim of this study was to evaluate the effects of surfactins topically applied on black bean aphid Aphis fabae mortality. First, the effects of surfactins on aphid mortality were determined by delivering increasing concentrations to adults and nymphs. Second, the sublethal effects of surfactins on locomotor activity and feeding behavior of surviving aphids were evaluated using the electropenetrography method. Finally, the effect of host exposure to surfactins on host selection behavior by Aphidius matricariae parasitoid females was analyzed.

RESULTS

Four surfactins concentrations were studied (0.5, 1, 2.5 and 5 g L^-1 ). There was concentration-dependent mortality in response to surfactins at 24 h after treatment. Surfactins impacted aphid behavior when delivered at 1 g L^-1 by inducing a greater locomotor activity and a reduction in feeding activity. By contrast, at the third trophic level, exposure of aphid hosts to surfactins did not affect behaviors leading to host recognition and acceptance by parasitoid females.

CONCLUSION

This study highlighted the consequences of aphid exposure to surfactins in the context of bottom-up regulation. Although surfactins could directly impact aphid behavior, they had no apparent consequences on the host selection behavior exhibited by parasitoid wasps.

Effects of Bacillus lipopeptides on the survival and behavior of the rosy apple aphid Dysaphis plantaginea

Within the framework of biocontrol development, several natural lipopeptides produced by Bacillus subtilis show well-documented anti-microbial properties, especially in orchards. However, the number of studies on their putative insecticidal effects remain low despite the growing interest to develop new strategies of orchards pests' control. The rosy apple aphid Dysaphis plantaginea is the major aphid pest causing great leaf damage to apple trees. In this study, we submitted young adult aphids to topical application of three different families of lipopeptides, Plipastatin (Fengycin), Mycosubtilin (Iturin), and Surfactin, either separately or as a ternary mixture. Their aphicidal effects were investigated at 1, 2.5 and 5 g/L, both at 1 h and 24 h after exposure, and their effects on aphid behavior were studied at the 2.5 g/L concentration at 24 h after exposure. When delivered alone, lipopeptides displayed contrasted effects varying from no aphicidal activity for Mycosubtilin to a mortality induced even at low concentrations by Surfactin. Surprisingly, locomotor activity of the surviving aphids was only affected by the two least lethal treatments, Mycosubtilin and the ternary mix. Their feeding behavior was only impacted by Surfactin, the most lethal treatment, that unexpectedly increased phloem sap ingestion. The results are discussed in the context of lipopeptides applicability for integrated pest management.

Identification of Volatile Organic Compounds in Extremophilic Bacteria and Their Effective Use in Biocontrol of Postharvest Fungal Phytopathogens

Phytopathogenic fungal growth in postharvest fruits and vegetables is responsible for 20-25% of production losses. Volatile organic compounds (VOCs) have been gaining importance in the food industry as a safe and ecofriendly alternative to pesticides for combating these phytopathogenic fungi. In this study, we analysed the ability of some VOCs produced by strains of the genera Bacillus, Peribacillus, Pseudomonas, Psychrobacillus and Staphylococcus to inhibit the growth of Alternaria alternata, Botrytis cinerea, Fusarium oxysporum, Fusarium solani, Monilinia fructicola, Monilinia laxa and Sclerotinia sclerotiorum, in vitro and in vivo. We analysed bacterial VOCs by using GC/MS and 87 volatile compounds were identified, in particular acetoin, acetic acid, 2,3-butanediol, isopentanol, dimethyl disulphide and isopentyl isobutanoate. In vitro growth inhibition assays and in vivo experiments using cherry fruits showed that the best producers of VOCs, Bacillus atrophaeus L193, Bacillus velezensis XT1 and Psychrobacillus vulpis Z8, exhibited the highest antifungal activity against B. cinerea, M. fructicola and M. laxa, which highlights the potential of these strains to control postharvest diseases. Transmission electron microscopy micrographs of bacterial VOC-treated fungi clearly showed antifungal activity which led to an intense degeneration of cellular components of mycelium and cell death.

Honey bee-associated bacteria as producers of bioactive compounds for protecting hives. A biosynthetic gene-based approach

Honey bee-associated bacteria are a source of natural compounds of interest for controlling hive decline which is threatening bee health globally. Genes involved in the biosynthesis of a series of extracellular compounds released by bacteria living on the external surface of honey bees were investigated. A biosynthetic gene-based approach was adopted by developing a battery of primers to target the genes involved in the biosynthesis of four groups of bioactive compounds (pyrrolizidine alkaloids, surfactin, 2-heptanone and helveticin J). The primers were tested on 51 bacterial isolates belonging to Bacillus thuringiensis, Acetobacteraceae bacterium, Bifidobacterium asteroides and Apilactobacillus kunkeei. The developed primers led to species-specific detection and characterization of the functional genes involved in the production of three out of four groups of compounds selected for this study. The findings suggest that microbial populations inhabiting apiaries harbor genes involved in the biosynthesis of metabolites linked to the reduction of important honey bee pathogens such as Varroa destructor, Paenibacillus larvae and Nosema ceranae. The gene-based approach adopted for evaluating the biosynthetic potential of bioactive compounds in hives is promising for investigating further compounds for low input control strategies of bee enemies.

Evaluation by MALDI-TOF MS and PCA of the diversity of biosurfactants and their producing bacteria, as adaption to weathered oil components

Indigenous Qatari bacterial strains were isolated from highly weathered oil-contaminated sites, identified, and differentiated based on their protein profiles using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Their diversity was demonstrated by the principal component analysis (PCA) analysis and establishment of a proteodendogram. Both were based on the protein profile of each strain. Interestingly, this approach also showed diversity within the same subspecies. This high diversity is reflected in the emulsification and solubilization activities of their extracellular biosurfactants. The highest emulsification activity (42.1 ± 2.11 AU/mL) was obtained with a strain of Lysinibacillus fusiformis (SA4) after one week of growth in the minimum salt medium in which diesel (5%) is the sole carbon source, while the highest solubilization activity (9.47% ± 0.47%) was produced by the strain Bacillus subtilis (SA6). The functional diversity of the biosurfactants was demonstrated by PCA analysis which allowed their further clustering based on the Fourier-transform infrared spectroscopy (FTIR) analysis. These findings clearly showed that two types of adaptations occur with hydrocarbons degrading bacteria in the weathered-oily soils, one related to the bacterial cell composition maintaining the biosurfactants composition and one to the biosurfactants, which are the primary tool employed by the cell to interact with the weathered oil. This finding would shed light on the potential and strategies of applications for the bioremediation of highly weathered oil-contaminated soils.

Microbial Toxins in Insect and Nematode Pest Biocontrol

Invertebrate pests, such as insects and nematodes, not only cause or transmit human and livestock diseases but also impose serious crop losses by direct injury as well as vectoring pathogenic microbes. The damage is global but greater in developing countries, where human health and food security are more at risk. Although synthetic pesticides have been in use, biological control measures offer advantages via their biodegradability, environmental safety and precise targeting. This is amply demonstrated by the successful and widespread use of Bacillusthuringiensis to control mosquitos and many plant pests, the latter by the transgenic expression of insecticidal proteins from B. thuringiensis in crop plants. Here, I discuss the prospects of using bacterial and fungal toxins for pest control, including the molecular basis of their biocidal activity.

Antiviral activity by lecithin-induced fengycin lipopeptides as a potent key substrate against Cucumber mosaic virus

In this study, the effect of different growth substrates on the production of biosurfactants in the PPL strain of Bacillus amyloliquefaciens-a biocontrol agent for diseases affecting pepper and tomato plants-and on the antiviral effect of the PPL strain on Cucumber mosaic virus (CMV)-infected pepper plants was investigated. The multifunctional PPL strain exhibited enhanced growth and increased production of biosurfactants upon lecithin supplementation and consequently exhibited potent anti-CMV activity. The enhanced anti-CMV activity of the lecithin-supplemented PPL culture could be attributed to the antiviral effect as well as to the upregulation of plant defense-related genes. Treatment with pure commercial fengycins elicited a defense response against CMV in pepper plants; this effect was similar to that observed upon treatment with the lecithin-supplemented PPL culture. To the best of our knowledge, this is the first study to report the antiviral activity of lecithin-induced fengycin lipopeptides. These results suggest that the growth substrate affects antimicrobial production by B. amyloliquefaciens PPL, and consequently its antiviral activity.

Endophytic Bacillus bacteria with RNase activity in the resistance of potato plants to viruses

Viral diseases annually cause significant crop losses and significantly reduce the quality of products, including potatoes, some of the most important crops. Currently, viruses cannot be controlled with chemical pesticides, since known antiviral compounds are teratogenic and hazardous to people’s health. Biocontrol agents based on endophytic microorganisms may be an alternative to them. Many strains of Bacillus produce ribonucleases (RNases). Our laboratory possesses a collection of bacteria that produce various metabolites and have RNase activity. The results showed that the inoculation of potato with B. subtilis 26D and B. thuringiensis increased the grain yield by 32–43 %. In addition, the treatment of potato plants with Bacillus spp. significantly reduced the infection of potato plants with virus M. The prevalence of the disease in potato plants was significantly reduced from 60 % in the control to 18 % (B. subtillis 26D) and 25–33 % (B. thuringiensis) in the inoculated plants. Similarly, the infection index decreased from 14 in the control to 1 in the inoculated plants. The further study of molecular mechanisms related to bacterial induction of plant defense reactions in response to viral infections will lead to a better understanding of stress resistance problems. The endophytic microorganisms studied in this report may become the basis for the creation of biological agents for plant protection.