Surfactin and Spo0A-Dependent Antagonism by Bacillus subtilis Strain UD1022 against Medicago sativa Phytopathogens

Abstract

Plant growth-promoting rhizobacteria (PGPR) such as the root colonizers Bacillus spp. may be ideal alternatives to chemical crop treatments. This work sought to extend the application of the broadly active PGPR UD1022 to Medicago sativa (alfalfa). Alfalfa is susceptible to many phytopathogens resulting in losses of crop yield and nutrient value. UD1022 was cocultured with four alfalfa pathogen strains to test antagonism. We found UD1022 to be directly antagonistic toward Collectotrichum trifolii, Ascochyta medicaginicola (formerly Phoma medicaginis), and Phytophthora medicaginis, and not toward Fusarium oxysporum f. sp. medicaginis. Using mutant UD1022 strains lacking genes in the nonribosomal peptide (NRP) and biofilm pathways, we tested antagonism against A. medicaginicola StC 306-5 and P. medicaginis A2A1. The NRP surfactin may have a role in the antagonism toward the ascomycete StC 306-5. Antagonism toward A2A1 may be influenced by B. subtilis biofilm pathway components. The B. subtilis central regulator of both surfactin and biofilm pathways Spo0A was required for the antagonism of both phytopathogens. The results of this study indicate that the PGPR UD1022 would be a good candidate for further investigations into its antagonistic activities against C. trifolii, A. medicaginicola, and P. medicaginis in plant and field studies.

Role of Bacillus subtilis exopolymeric genes in modulating rhizosphere microbiome assembly

“…Previous studies have shown that the Bacillus subtilis strain UD1022 exerts beneficial effects on plant growth and offers protection against plant pathogens [ 13 , 23 , 45 , 46 , 53 ]. Most experiments involving plant growth-promoting rhizobacteria (PGPR) are conducted using artificial soil or under controlled laboratory conditions [ 70 ].…”

“…The B. subtilis strain UD1022 eps−TasA− , which is defective for the EPS and TasA genes, was obtained in a previous study [ 53 ]. Wild-type B. subtilis was cultivated on Luria broth (LB) agar plates, and its respective mutant was cultivated on LB supplemented with 5 µg mL −1 tetracycline and 1 µg mL −1 erythromycin.…”

Alfalfa Spring Black Stem and Leaf Spot Disease Caused by Phoma medicaginis: Epidemic Occurrence and Impacts

“…Biological control methods are also available for the control of ASBS. Leaf lesion areas pre-colonized by P. medicaginis failed to develop, when those lesions were sprayed with conidial suspensions of Cladosporium cladosporioides or Penicillium citrinum [88], with AM fungi Funneliformis mosseae or Rhizophagus intraradices, with the rhizobium Sinorhizobium medicae [89,90], and with Bacillus licheniformis [91] or with B. subtilis [92]. Also, Streptomyces inoculated onto the seed at the time of planting or onto leaves also showed potential to reduce leaf spot caused by P. medicaginis incidence and index under greenhouse conditions [88].…”

“…B. subtilis strain L194 also alleviates disease symptoms by reducing germination of P. medicaginis conidia [95]. B. subtilis strain UD1022 is directly antagonistic not only towards P. medicaginis, but also towards Collectotrichum trifolii and Phytophthora medicaginis [92]. B. subtilis can also control alfalfa root rot disease.…”

“…antibiotics, were regarded as playing an important role in the antagonism of Bacillus spp. towards P. medicaginis [92].…”