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

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