Cyanide degradation and antagonistic potential of endophytic Bacillus subtilis strain BEB1 from Bougainvillea spectabilis Willd

Bacterial endophytes were isolated from the leaves of Bougainvillea spectabilis Willd. and screened for their in vitro antagonistic activity against three important phytopathogenic fungi viz., Neocosmospora keratoplastica, Stemphylium vesicarium and Rhizoctonia solani. Among the 36 endophytic bacterial isolates screened, three isolates designated as BEB1, BEB5 and BEB6 inhibited the mycelial growth of all the three plant pathogenic fungi tested and recorded more than 10% growth inhibition. Scanning electron microscopic observations of hyphae of the pathogenic fungi at the periphery of the inhibition zone in the dual culture plate revealed morphological abnormalities such as shrinkage, pit formation and loss of turgidity. These isolates were identified as Bacillus subtilis (BEB1) and Bacillus cereus (BEB5 and BEB6) based on the MALDI Biotyper analysis. The Bacillus subtilis strain BEB1, which exhibited the highest level of antagonism, was tested for its sensitivity to cyanide and potential to degrade NaCN. The results revealed that this strain was capable of growing in a medium containing 5 mM of NaCN with a degradation efficiency of 53.8%. This endophyte is valuable for exploitation as a biocontrol agent to control diseases especially in the cyanogenic plants and bioremediation of cyanide from the industrial effluent.