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

Food 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.