Applied Microbiology: Open Access
Open Access

Abstract

Identification of Endophytic Bacteria and their Characterization as Biocontrol Agents against Tomato Southern Blight Disease

Claudia Mónica Ribaudo, Daniela Soledad Riva, Juan Ignacio Gori, José Ignacio Zaballa and Catalina Molina

Objectives: The purpose of the present study was to characterize the endophytic bacterium PAC BNM0522 and to evaluate its role in the ethylene signaling pathway in the development of southern blight disease (caused by the necrotrophic fungus Sclerotium rolfsii) in tomato plants. Methods: In this study, biochemical tests, 16S rRNA gene sequencing, and amplification of the ACCD gene (acdS) were performed on the isolate obtained from pruning compost. This isolate was also screened for antibiotic production and competition for nutrients and evaluated its role in the ethylene signaling pathway by analysis of the expression of genes involved in ethylene biosynthesis by PCR and ethylene content by GC. Results: The analysis of the 16S rRNA gene partial sequence and biochemical test placed this bacterium within the genus Pseudomonas and revealed that it belongs to the group of PGPR with multiple plant growth-promoting traits. This rhizobacterium was able to promote host growth through direct antagonism to the fungal pathogen. The in vivo experiments showed that PAC BNM0522 inoculation controlled the disease caused by S. rolfsii. The ethylene level was enhanced in tomato plants infected with the fungus and decreased by inoculation of the rhizobacterium. The expression of the Sl-ACS2 isoform was induced by the presence of the pathogen and strongly repressed in PAC BNM0522-primed plants. The accumulation of the Sl-ACO1 messenger was down-regulated in deaminaseproducing PAC BNM0522-inoculated plants. Conclusion: Our results indicate that ACCD-containing PAC BNM0522 generated protection of tomato plants under pathogenic stress and alleviated ethylene-induced damage, by regulating the expression of genes involved in the ethylene pathway. PAC BNM0522 may be used as an alternative ecological approach to control soil-borne fungi.