Novel Cell-Free Suspensions of Symbiotic Bacteria for Biocontrol of Phytopathogenic Bacteria

Biofertilizers utilize plant growth-promoting bacteria (PGPB), which are symbiotic bacteria found in the root nodules of leguminous plants that fix atmospheric nitrogen. This study utilized cell-free bacterial suspensions from several leguminous plants, including Vicia faba, Trifolium repens, Lens culinaris, Trigonella foenum-graecum, Lens culinaris subsp. orientalis and Medicago sativa. Six isolates (MA1–MA6) were tested as biocontrol agents against Agrobacterium tumefaciens RB04, Lelliottia amnigena MN1 and Xanthomonas campestris. After establishing that these bacteria are pathogenic, we evaluated their antagonistic activity using the cross method. This identified MA2 as the most effective isolate, with MA5 following closely. Among the tested isolates, MA2 was the most successful in inhibiting the growth of pathogenic bacteria, followed by MA5. The other isolates only impacted the growth of two bacterial species: L. amnigena strain MN1 and X campestris. The agar well diffusion method showed bacterial sensitivity to cell-free supernatants (CFSs) at 67%, 34% and 17% for A. tumefaciens, X. campestris and L. amnigena, respectively. CFS MA6, the most effective supernatant, was analyzed via gas chromatography-mass spectrometry, revealing four active compounds: C7H13NO2, C11H18N2O2, C28H53NO3 and C21H39NO3, with molecular weights of 143, 210, 451 and 353, respectively. KEYWORDS Agrobacterium tumefaciens, antagonistic, biofertilizers, GC-MS, legume plants, PGPB