Evaluation of quorum quenching Bacillus spp. for their biocontrol traits against Pectobacterium carotovorum subsp. carotovorum causing soft rot

Pectobacterium carotovorum subsp. carotovorum (Pcc) is an important broad host range, soft rot causing phytopathogen with multiple modes of infection. AHL mediated quorum sensing mechanism plays a pivotal role in pathogenesis of Pcc, by regulating its major virulence enzymes that degrade plant cell wall. Here, the disruption of quorum sensing as a strategy for biocontrol of Pcc is proposed, especially in the light of rising antimicrobial resistance. Bacillus based biocontrol agents have been found useful in management of bacterial and fungal plant diseases. Additionally, they are known to produce AHL lactonase that inactivates AHL signalling in quorum sensing. Since prior to use in the field, a bacterial strain should be tested for its efficacy and amenability as biocontrol agent, the focus of the present studies was to evaluate the traits that bestow the biocontrol attributes to the isolates so as to be an effective biocontrol agent. Keeping in view this, 97 isolates screened for AHL degradation from root and soil yielded 20 AHL degrading Bacillus spp. out of which three isolates As30, Gs42 and Gs52 were selected since they demonstrated appreciable attenuation of Pcc soft rot. Moreover, the attenuation was observed in both curative and preventive biocontrol studies. The root colonisation ability and in planta studies of prevention of mung bean spoilage further demonstrated that the isolates have high potential to reduce the disease. The studies conducted in this work suggests that soil quorum quenching soil Bacillus isolates have the attributes to be taken for further application studies.