Antioxidant power of phytochemicals from Psidium guajava leaf.

ried ground leaves of Psidium guajava L. (guava) were extracted by water and aqueous ethyl alcohol 50% (1:10) ratio, and the total phenolic content in the extracts was determined spectrophotometrically according to Folin- Ciocalteu's phenol method and calculated as gallic acid equivalent (GAE). Remarkably high total phenolic content 575.3 +/-15.5 and 511.6+/-6.2 mg of GAE/g of dried weight material (for ethanol guava leaf extracts and water guava leaf extracts, respectively) were obtained. The antioxidant activity of lyophilized extracts was determined at ambient temperature by means of a 2,2-diphenyl-1-picrylhydryzyl (DPPH*) colorimetry with detection scheme at 515 nm. The activity was evaluated by the decrease in absorbance as the result of DPPH* color change from purple to yellow. The higher the sample concentration used, the stronger was the free radical-scavenging effect. The results obtained showed that ascorbic acid was a substantially more powerful antioxidant than the extracts from guava leaf. On the other hand, the commercial guava leaf extracts and ethanol guava leaf extracts showed almost the same antioxidant power whereas water guava leaf extracts showed lower antioxidant activity. The parameter EC(50) and the time needed to reach the steady state to EC(50) concentration (T(EC(50))) affected the antiradical capacity of the sample. The antioxidant efficiency (AE) has been shown to be a more adequate parameter for selecting antioxidants than the widely used EC(50). This study revealed that guava leaf extracts comprise effective potential source of natural antioxidants

Separation and identification of endoxylanases from Bacillus subtilis and their actions on wheat bran insoluble dietary fibre

A novel and convenient method based on native polyacrylamide gel electrophoresis (PAGE) and homogenization extraction was used for the purification of xylanase from crude enzymes. Two xylanases were purified by this method from the crude enzyme preparation from the selected strain of Bacillus subtilis. Subsequent analysis with thin layer chromatography and high pressure liquid chromatography (HPLC) indicated that these two xylanases were endo-acting enzymes, designated xyl I and xyl II. Both enzymes showed their activities in the pH range from 5.0 to 9.0 at 50 °C and had similar optimum activities at pH 7.0 and at 50 °C. Mn2+ ions enhanced their xylanolytic activities to 2.7-fold whereas Fe3+ completely inhibited them. The action of endoxylanase xyl II on wheat bran insoluble dietary fibre was also studied. The hydrolysis products were shown to contain feruloyl oligosaccharides by paper chromatograph

Production des lipopeptides dans la rhizosphère par Bacillus en tant que mécanisme impliqué dans le contrôle biologique des agents pathogènes des plantes

Some plant-beneficial bacteria with biopesticide potential produce antimicrobial compounds that are tightly involved in multitrophic interactions occurring in the phytosphere among which antagonism toward a diverse range of phytopathogens. However, there is a crucial need for an accurate assessment of antibiotic production rate in this environment colonized by these bacteria. In this context, we conducted the present thesis work with the scope to better understand how two different Bacillus genus strains produce lipopeptides in the rhizosphere of plants. In the first part, one of the strains (B. amyloliquefaciens S499) was selected out of other isolates for its technological traits and in vitro inhibition growth activity of plant pathogenic fungi. We further demonstrated its biocontrol potential in tomato open-field experiments where plantings have been devastated by a local fungus preliminary identified as Fusarium semitectum. In a second part, we combined two mass spectrometry-based approaches (electrospray ionization and imaging) to analyze the pattern of surfactin, iturin and fengycin lipopeptide families produced in planta by strain S499. Our results show that rhizosphere conditions are conducive for surfactin synthesis but not for other types of lipopeptides and that the lipopeptide pattern can be markedly influenced by nutritional factors, biofilm formation and oxygen availability. In a last part, surfactin gene expression (srfA) level was evaluated in situ on tomato root using the reporter gene (LacZ) inserted in B. subtilis strain BGS3. Results showed effective expression of srfA and production of surfactin in biologically important level quantities upon establishment of bacterial population on roots. Our results also demonstrate that BGS3 developing in colonies, efficiently utilizes the main substrates from plant exudates to produce surfactins. The production may also be favored in bacteria growing slowly in the rhizosphere. Globally, this work contributes to better appreciate the impact of some environmental factors on the in situ biosynthesis of lipopeptides by strains of Bacillus which is probably an essential step for improving the level and reliability of their efficacy as biological agents for the control of plant diseases

Bacillus-based biocontrol beyond chemical control in central Africa: the challenge of turning myth into reality

Agricultural productivity in the Great Lakes Countries of Central Africa, including Burundi, Rwanda, and the Democratic Republic of Congo, is affected by a wide range of diseases and pests which are mainly controlled by chemical pesticides. However, more than 30% of the pesticides used in the region are banned in European Union due to their high toxicity. Globally available safe and ecofriendly biological alternatives to chemicals are virtually non-existent in the region. Bacillus PGPRbased biocontrol products are the most dominant in the market and have proven their efficacy in controlling major plant diseases reported in the region. With this review, we present the current situation of disease and pest management and urges the need to utilize Bacillus-based control as a possible sustainable alternative to chemical pesticides. A repertoire of strains from the Bacillus subtilis group that have shown great potential to antagonize local pathogens is provided, and efforts to promote their use, as well as the search for indigenous and more adapted Bacillus strains to local agro-ecological conditions, should be undertaken to make sustainable agriculture a reality in the region

Isolation, antagonistic activity, chemical characterization of soil-borne and plant-beneficial bacteria from Burundi

peer reviewedFood production is worldwide threatened by plant diseases and pests, which are responsible of about 10% of loss of the global food production (Strange & Scott, 2005). Chemical pesticides have been for long utilized for fighting those pests and increment crop harvests. However, the adverse effects of the conventional pesticides on environment and human kind appealed the international community to search for alternative solutions. Plant Beneficial microorganisms with pathogen antagonistic and plant resistance inducing activities could be an ecofriendly option to boost crop yields and limit those deleterious effects (Adedeji et al., 2020). In our work, nineteen bacterial strains were isolated from arable soils samples collected from two different agro-ecological locations in Burundi (Murwi-Cibitoke province and Isale-Bujumbura province). Six bacterial isolates exhibited great antibacterial activity against five of the six selected plant pathogenic bacteria (Two gram positive and four gram negative). One particular bacterial isolate was however active against all the six plant pathogens to an extent comparable or greater than the reference bacteria’s activity. For instance, that isolate inhibited cereals’ brown sheath rot (Pseudomonas fuscovaginae) at a rate of 150% compared to Bacillus velezensis GA1 activity. The 16S rRNA sequencing revealed that five isolates belong to Bacillus pumilus strains and the best candidate belong to Bacillus nakamurai strains. Culture supernatants analyses by LC/Q-TOF mass spectrometry showed that the B. pumilus strains produce pumilacidin among other unknown compounds, while the B. nakamurai strain produce cyclic lipopeptides (surfactins and iturins), polyketides and siderophores. One important peak on the mass spectrum seem to be an unknown fengycin (research ongoing). Further analyses including pattern fragmentation are required to determine the nature of that compound. Green house and in planta experiments with that promising candidate (belonging to B. nakamurai strains) constitute the forefront activities to be carried out for efficacy assessment. These findings suggest that Burundi soils are a reservoir of plant beneficial bacteria that may be utilized in plant diseases management.2. Zero hunge

Ecological fitness of Bacillus subtilis BGS3 regarding production of the surfactin lipopeptide in the rhizosphere

peer reviewedaudience: researcher, professionalCyclic lipopeptides and particularly surfactins produced by Bacillus species retain antibacterial, antiviral, biofilm-forming and plant resistance-inducing activities. In most cases, their role in biological control of plant diseases was evoked on the basis of in vitro assays or by using non-producing/ overproducing mutants but there is a need for more direct evidence of an efficient lipopeptide biosynthesis in the rhizosphere. In this work, we coupled LC-MS quantification of the lipopeptides secreted by cells colonizing tomato plants with the use of psrfA– lacZ reporter system integrated within the BGS3 chromosome to study the expression of the surfactin operon in planta. Results showed that a higher level of psrfA induction was observed upon the establishment of a stable BGS3 population on roots and surfactins extracted from the rhizosphere were produced in biologically significant quantities. Our results also demonstrate that BGS3 efficiently utilizes the main substrates from plant exudates to produce surfactins. This synthesis is also efficient in cells forming colonies and the production may be favoured in bacteria developing slowly in the rhizosphere. This provides a first understanding of how environmental factors may influence lipopeptide production by beneficial Bacillus strains.Gembloux Agro-Bio tec

Characterization of a new Bacillus nakamurai soil isolate with strong antimicrobial and biocontrol potential

peer reviewedSince the last decades, the use of bacterial isolates to reduce or replace chemical pesticides has grown in importance. In that respect, the isolation of new promising plant-beneficial bacteria represents the first step to bring new efficient biocontrol products on the market. With that idea, several strains were isolated from soil samples collected from two different agro-ecological locations in Burundi. First, all these isolates were evaluated for their antimicrobial activities against a range of bacterial and fungal phytopathogens including species isolated from Burundian diseased crops. Among those beneficial isolates, the strain BDI-IS1 has been selected based on its highest antimicrobial potential. Indeed, this strain inhibited all the selected bacterial and fungal phytopathogens with similar efficacy as the commercialized strain B. velezensis QST713 (Serenade). Based on genome sequencing, this isolate has been classified as member of the poorly described Bacillus nakamurai species. Bioassays indicated that some soluble secondary metabolites produced by this strain are tightly involved in the antagonistic activities. Genome mining coupled with metabolomic studies revealed the diversity of structurally different compounds produced by this isolate, including dipeptides, non-ribosomally synthesized peptides and polyketides as well as ribosomally synthesized and post-translationally modified peptides. Understanding the involvement of each metabolite in the antimicrobial activities is being investigated, but these findings strongly suggest that this B. nakamurai BDI-IS1 strain can be considered as a good candidate in terms of biocontrol.2. Zero hunge

Ecological fitness of Bacillus subtilis BGS3 regarding production of the surfactin lipopeptide in the rhizosphere

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