Antifungal effect and some properties of cell-free supernatants of two Bacillus subtilis isolates against Fusarium verticillioides

Fusarium verticillioides causes significant decrease in corn yield and quality, and produces fumonisins, which represent a serious risk to human and animal health. Bacillus species can be an effective and environmentally friendly alternative for F. verticillioides biological control. In this study, some properties of cell-free supernatants (CFSs) of two Bacillus spp. identified as Bacillus subtilis (NT1, NT2) as well as the antifungal effect against F. verticillioides 97L were evaluated. B. subtilis NT1 and NT2 were isolated from commercially available fermented whole soybeans (Nattō). Antifungal activity was observed in both CFSs of B. subtilis isolates (50-59 mm) obtained by co-culture suggesting that antifungal compound production depends on interaction between bacteria and fungi. Cell-free supernatants from the two B. subtilis isolates inhibited mycelial growth (77%-94%) and conidial germination (22%-74%) of F. verticillioides 97L. In addition, CFSs caused significant morphological changes such as distorted and collapsed hyphae with wrinkled surfaces and the presence of a large amount of extracellular material compared to the control without CFSs. Both B. subtilis isolates (NT1 and NT2) produced extracellular proteases, biosurfactants and polar low molecular weight compounds that probably act synergistically and may contribute to the antifungal activity. Antifungal compounds showed heat and pH stability and resistance to proteolytic enzymes. Furthermore, antifungal compounds showed high polarity, high affinity to water and a molecular weight less than 10 kDa. These results indicated that the two B. subtilis (NT1 and NT2) have potential as biocontrol agents for F. verticillioides.

The Prospect of Hydrolytic Enzymes from Bacillus Species in the Biological Control of Pests and Diseases in Forest and Fruit Tree Production

Plant diseases and insect pest damage cause tremendous losses in forestry and fruit tree production. Even though chemical pesticides have been effective in the control of plant diseases and insect pests for several decades, they are increasingly becoming undesirable due to their toxic residues that affect human life, animals, and the environment, as well as the growing challenge of pesticide resistance. In this study, we review the potential of hydrolytic enzymes from Bacillus species such as chitinases, β-1,3-glucanases, proteases, lipases, amylases, and cellulases in the biological control of phytopathogens and insect pests, which could be a more sustainable alternative to chemical pesticides. This study highlights the application potential of the hydrolytic enzymes from different Bacillus sp. as effective biocontrol alternatives against phytopathogens/insect pests through the degradation of cell wall/insect cuticles, which are mainly composed of structural polysaccharides like chitins, β-glucans, glycoproteins, and lipids. This study demonstrates the prospects for applying hydrolytic enzymes from Bacillus sp. as effective biopesticides in forest and fruit tree production, their mode of biocidal activity and dual antimicrobial/insecticidal potential, which indicates a great prospect for the simultaneous biocontrol of pests/diseases. Further research should focus on optimizing the production of hydrolytic enzymes, and the antimicrobial/insecticidal synergism of different Bacillus sp. which could facilitate the simultaneous biocontrol of pests and diseases in forest and fruit tree production.

Biochemical compositions and histopathology of the young and aged nymphs of the desert locust Schistocerca gregaria Forsskål (Orthoptera: Acrididae) affected by Photorhabdus luminescens (Enterobacterales: Morganellaceae)

Locusts occasionally represent a danger in Africa despite intensive management measures, leading to severe yield loss and a commensurate loss of food and money. The laboratory assessment of the toxicity of the Photorhabdus luminescens bacteria and its cell-free filtrate used Schistocerca gregaria nymphs in the second and fifth nymphs as test insects. Greater mortality was seen in locust nymphs of the second and fifth instars due to the high levels of toxicity produced by the bacterial suspension and its cell-free filtrate. The amounts of protein, fat, and carbohydrates in the treated locusts were drastically reduced. For the treated second and fifth instar nymphs of the desert locust, adverse effects on the muscular layers of the midgut and the muscles in the jumping legs were investigated.

Effect of Probiotics on Tenebrio molitor Larval Development and Resistance against the Fungal Pathogen Metarhizium brunneum

In recent years, the yellow mealworm (Tenebrio molitor L.) has demonstrated its potential as a mass-produced edible insect for food and feed. However, challenges brought on by pathogens in intensive production systems are unavoidable and require the development of new solutions. One potential solution is the supplementation of probiotics in the insect's diet to obtain the double benefits of improved growth and enhanced immune response. The aim of this study was to evaluate the effects of diet-based probiotic supplementation on T. molitor larval survival, growth, and resistance against a fungal pathogen. Three probiotic strains, namely Pediococcus pentosacceus KVL-B19-01 isolated from T. molitor and two commercialized strains for traditional livestock, Enterococcus faecium 669 and Bacillus subtilis 597, were tested. Additionally, when larvae were 9 weeks old, a pathogen challenge experiment was conducted with the fungus Metarhizium brunneum. Results showed that both P. pentosaceus and E. faecium improved larval growth and larval survival following fungal exposure compared to the non-supplemented control diet. Since B. subtilis did not improve larval performance in terms of either development or protection against M. brunneum, this study suggests the need for further research and evaluation of probiotic strains and their modes of action when considered as a supplement in T. molitor's diet.

Characterization of Bacillus velezensis RDA1 as a Biological Control Agent against White Root Rot Disease Caused by Rosellinia necatrix

White root rot disease, caused by Rosellinia necatrix, poses a threat to several tree crops; hence, effective and sustainable strategies to control this disease remain warranted. This study identified an effective R. necatrix biocontrol agent by isolating 32 strains from soil samples collected from white root rot-infested organic pear orchards, among which RDA1 exhibited the most potent growth-inhibitory effects. Microbiological and 16S rRNA gene sequencing analyses revealed that the bacterial isolate belonged to the Bacillus genus and exhibited 100% nucleotide sequence similarity with Bacillus velezensis species in the GenBank. This strain showed strong antifungal activity against four Rosellinia necatrix strains and harbored genes essential for lipopeptide, polyketide, and tripeptide bacilysin biosynthesis. RDA1 produced volatile compounds that suppressed the development of phytopathogens and possessed plant growth-promoting traits, such as phosphate solubilization, and indole-3-acetic acid and siderophore production. B. velezensis RDA1 has a significant potential application in sustainable agriculture and can be used to suppress white root rot disease infections and to improve plant growth.

Molecular Identification, Characterization and Improvement of A Chitinase Producing Bacillus strain Showing Significant Control against Some Dermatophytic Fungi

Bacillus bacteria are advantageous antagonistic organisms that can be used as bio-control agents. This study is aimed at screening the antagonistic activity of different strains of isolated Bacillus bacteria and molecular identification of the superior chitinase producer strain against dermatophytes fungi. Soil samples were collected from different places of Kotoor city, Gharbia Governorate, Egypt and Al Madina Al Munawwarah, Kingdom of Saudi Arabia. A collection of Bacillus isolated from soil was tested in vitro against the dermatophytes: Microsporum sp. and Trichophyton sp. The bacterial strains Kh-B1 and Kh-B2 showed the highest antagonistic activity against dermatophytes pathogenic fungi. The highest amount of chitinase productivity (13.6 units/ml) was obtained from the original Bacillus strain (Kh-B1) at 3 days of incubation. BLAST analysis of the amplified 16S ribosomal RNA gene sequence identified the Bacillus strain (Kh-B1) as Paenibacillus macerans. Upon the mutation induction by UV light, the highest chitinase-producing mutant was Kh-UVB-4 as it showed 305.88 percent production higher than the wild-type strain. While, upon the mutation induction by EMS, the highest amount of chitinase produced was 54.8 units/ml by mutant Kh-ESB-20, and it has produced 402.94% more than the original untreated strain. The application of RAPD-PCR protocol using three 15-mer random primers was used to determine the genetic effects of mutagenic treatments on the wild type strain (Kh-B1) as well as to demonstrate the genetic variability between the five most chitinase producing mutants and the wild type (Paenibacillus macerans).

An Endophytic Strain of Bacillus amyloliquefaciens Suppresses Fusarium oxysporum Infection of Chinese Wolfberry by Altering Its Rhizosphere Bacterial Community

Root rot disease is a serious infection leading to production loss of Chinese wolfberry (Lycium barbarum). This study tested the potential for two bacterial biological control agents, Bacillus amyloliquefaciens HSB1 and FZB42, against five fungal pathogens that frequently cause root rot in Chinese wolfberry. Both HSB1 and FZB42 were found to inhibit fungal mycelial growth, in vitro and in planta, as well as to promote the growth of wolfberry seedlings. In fact, a biocontrol experiment showed efficiency of 100% with at least one treatment involving each biocontrol strain against Fusarium oxysporum. Metagenomic sequencing was used to assess bacterial community shifts in the wolfberry rhizosphere upon introduction of each biocontrol strain. Results showed that HSB1 and FZB42 differentially altered the abundances of different taxa present and positively influenced various functions of inherent wolfberry rhizosphere bacteria. This study highlights the application of biocontrol method in the suppression of fungal pathogens that cause root rot disease in wolfberry, which is useful for agricultural extension agents and commercial growers.

Optimization of Growth Conditions for the Production of Bacillus subtilis Using Central Composite Design and Its Antagonism Against Pathogenic Fungi

Today, the enhancement of spore yields of Bacillus subtilis has considerable interest and has been widely investigated. In this context, studies have been carried out to improve the spore yield as well as the production amount. In order to perform this, optimization studies are conducted for large-scale production of B. subtilis in bioreactors. The prokaryotic structure, high extracellular production potential, lack of pathogenic activity, well-known fermentation technology and short fermentation time are the prominent advantages for the production of B. subtilis in a bioreactor. The Bacillus species produce a wide variety of antifungal and antimicrobial compounds, making them ideal biological control agents. In this study, first, the growth conditions of the medium were investigated and then optimized using the central composite design approach to achieve the highest productivity for the growth of B. subtilis. In the experiments, the effect of temperature of 25, 30 and 35 °C and pH level of 6.0, 7.0 and 8.0 on spore yield was studied. Moreover, the antifungal activity of the B. subtilis culture was investigated against pathogenic fungi: Colletotrichum gloeosporioides, Botrytis cinerea and Aspergillus brasiliensis.

Supplementation of Bacillus subtilis GM5 enhances broiler body weight gain and modulates cecal microbiota

We investigated the effect of the strain Bacillus subtilis GM5 on growth, feed conversion, and the composition of cecum microbiota in broiler chickens. Half of which received a control diet, while the other half was fed a diet supplemented with GM5 spores. Cecal contents on days 1, 10, and 42 were subjected to metataxonomic analysis. Principal Component Analysis showed that the control and probiotic groups formed three separate clusters, indicating changes, which occurred gradually in microbial communities. On day 1, Firmicutes (53.87-57.61%) and Proteobacteria (43.77-38.93%) were prevalent in both groups, whereas samples of days 10 and 42 were predominantly occupied by Firmicutes (54.55-81.79%) and Bacteroidetes (26.94-30.45%). In the group of chickens treated with probiotic, the average daily gain in body weight was higher, while feed conversion decreased by 1.44%. A surge in the presence of beneficial bacteria of the Ruminococcaceae family was observed. The introduction of the probiotic led to an elevated Firmicutes/Bacteroidetes ratio, which positively correlated with chickens' bodyweight (Spearman ρ = 1.0, P < 0.05). Supplementing broiler feed with B. subtilis GM5 spores leads to improved feed intake and digestibility, which is paramount in reducing the cost of the final product. Thus, the probiotic strain GM5 modulates the cecal microbiota of broiler chickens and increases microbial diversity, which is well exhibited on the 42nd day.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-020-02634-2.

Mecanismos de acción de <i>Bacillus</i> spp. (Bacillaceae) contra microorganismos fitopatógenos durante su interacción con plantas

Algunos Bacillus spp. promotores de crecimiento vegetal son microorganismos reconocidos como agentes de control biológico que forman una estructura de resistencia denominada endospora, que les permite sobrevivir en ambientes hostiles y estar en casi todos los agroecosistemas. Estos microorganismos han sido reportados como alternativa al uso de agroquímicos. Sus mecanismos de acción se pueden dividir en: producción de compuestos antimicrobianos, como son péptidos de síntesis no ribosomal (NRPs) y policétidos (PKs); producción de hormonas, capacidad de colonización, formación de biopelículas y competencia por espacio y nutrientes; síntesis de enzimas líticas como quitinasas, glucanasas, protesasas y acil homoserin lactonasas (AHSL); producción de compuestos orgánicos volátiles (VOCs); e inducción de resistencia sistémica (ISR). Estos mecanismos han sido reportados en la literatura en diversos estudios, principalmente llevados a cabo a nivel in vitro. Sin embargo, son pocos los estudios que contemplan la interacción dentro del sistema tritrófico: planta – microorganismos patógenos – Bacillus sp. (agente biocontrolador), a nivel in vivo. Es importante destacar que la actividad biocontroladora de los Bacillus es diferente cuando se estudia bajo condiciones de laboratorio, las cuales están sesgadas para lograr la máxima expresión de los mecanismos de acción. Por otra parte, a nivel in vivo, la interacción con la planta y el patógeno juegan un papel fundamental en la expresión de dichos mecanismos de acción, siendo esta más cercana a la situación real de campo. Esta revisión se centra en los mecanismos de acción de los Bacillus promotores de crecimiento vegetal, expresados bajo la interacción con la planta y el patógeno.

Bacillus Spp.: Efficient Biotic Strategy to Control Postharvest Diseases of Fruits and Vegetables

: Postharvest diseases significantly reduce the shelf-life of harvested fruits/vegetables worldwide. Bacillus spp. are considered to be an eco-friendly and bio-safe alternative to traditional chemical fungicides/bactericides due to their intrinsic ability to induce native anti-stress pathways in plants. This review compiles information from multiple scientific databases (Scopus, ScienceDirect, GoogleScholar, ResearchGate, etc.) using the keywords "postharvest diseases", "Bacillus", "Bacillus subtilis", "biocontrol", "storage", "losses", and "fruits/vegetables". To date, numerous examples of successful Bacillus spp. application in controlling various postharvest-emerged pathogens of different fruits/vegetables during handling, transportation, and storage have been described in the literature. The mechanism/s of such action is/are still largely unknown; however, it is suggested that they include: i) competition for space/nutrients with pathogens; ii) production of various bio-active substances with antibiotic activity and cell wall-degrading compounds; and iii) induction of systemic resistance. With that, Bacillus efficiency may depend on various factors including strain characteristics (epiphytes or endophytes), application methods (before or after harvest/storage), type of pathogens/hosts, etc. Endophytic B. subtilis-based products can be more effective because they colonize internal plant tissues and are less dependent on external environmental factors while protecting cells inside. Nevertheless, the mechanism/s of Bacillus action on harvested fruits/vegetables is largely unknown and requires further detailed investigations to fully realize their potential in agricultural/food industries.